per-row cell-run repaint

.gitignore

@@ -13,3 +13,4 @@ devenv.local.yaml
 build
 build
 .gradle
+bin

.ignore

@@ -0,0 +1,3 @@
+.gradle
+result
+bin

README.md

@@ -2,7 +2,15 @@
 
 JavaFX canvas terminal prototype using `jlibghostty` for terminal emulation and Nix for
 the build environment. It builds a plain JavaFX application (JDK 25, JavaFX 25 via Gradle)
-packaged as a Nix derivation — no GraalVM/GluonFX native image.
+packaged as a Nix derivation — no GraalVM/GluonFX native image. It supports tiled and
+floating panes and tabs.
+
+> [!CAUTION]
+> `nix profile add` has only been tested on **Debian with the proprietary NVIDIA driver**.
+> The runtime GL shim hardcodes Debian's `/lib/x86_64-linux-gnu` driver paths and selects
+> the NVIDIA GLX/EGL vendor, so it likely won't work yet on other distros, Wayland-only
+> setups, or Mesa/AMD/Intel GPUs. I'm happy to accept pull requests that broaden host
+> support.
 
 ## Build
 
@@ -11,7 +19,7 @@ nix build
 ./result/bin/jprototerm
 ```
 
-Install it into a profile (works on NixOS and on a plain Debian box with Nix installed):
+Install it into a profile (see the caution above on host support):
 
 ```sh
 nix profile add .
@@ -97,9 +105,11 @@ navigate_down = "ALT+J"
 navigate_up = "ALT+K"
 navigate_right = "ALT+L"
 toggle_floating = "ALT+F"
-new_floating = "ALT+SHIFT+F"
-next_floating = "ALT+F12"
+new_pane = "ALT+N"
 close_pane = "ALT+X"
+new_tab = "ALT+A"
+previous_tab = "ALT+SHIFT+H"
+next_tab = "ALT+SHIFT+L"
 open_font_selector = "ALT+T"
 open_scrollback = "ALT+S"
 ```
@@ -107,11 +117,18 @@ open_scrollback = "ALT+S"
 ## Defaults
 
 - `Alt+h/j/k/l`: navigate panes
+- `Alt+n`: new pane — a floating pane when floating panes are shown, otherwise a new tiled
+  pane (tiled panes are split equally across the width)
 - `Alt+f`: show or hide all floating panes
-- `Alt+Shift+f`: create a new floating pane
-- `Alt+F12`: cycle floating panes
-- `Alt+x`: close the active floating pane
+- `Alt+x`: close the active pane; closing a tab's last pane closes the tab, and closing the
+  last pane of the last tab quits
+- `Alt+a`: new tab
+- `Alt+Shift+h` / `Alt+Shift+l`: previous / next tab
 - `Alt+t`: open the font selector
 - `Alt+s`: open the active pane scrollback in `$EDITOR`
 - Font default: `JetBrainsMono Nerd Font`
 - Kitty graphics protocol parsing is enabled by default
+
+Each tab has its own stack of tiled and floating panes; only the active tab is rendered. A
+thin tab bar appears at the top when more than one tab is open. Closing the last tiled pane
+while floating panes exist promotes the most recently active floating pane to a tiled pane.

config.example.toml

@@ -25,8 +25,7 @@ navigate_down = "ALT+J"
 navigate_up = "ALT+K"
 navigate_right = "ALT+L"
 toggle_floating = "ALT+F"
-new_floating = "ALT+SHIFT+F"
-next_floating = "ALT+F12"
+new_pane = "ALT+N"
 close_pane = "ALT+X"
 open_font_selector = "ALT+T"
 open_scrollback = "ALT+S"

flake.lock

@@ -70,11 +70,11 @@
         "nixpkgs": "nixpkgs"
       },
       "locked": {
-        "lastModified": 1780050576,
-        "narHash": "sha256-u06xuO3QnLDpajIOZwDdhwI0HGzMuXG7x1pR+4Zb+RA=",
+        "lastModified": 1780079529,
+        "narHash": "sha256-AxlGTL8c5xSLcQHvWlm994IdOqxsN8iKrA02Cpv7vso=",
         "ref": "refs/heads/main",
-        "rev": "d558d554b360a76d03c2fc09d327e3ec4aade878",
-        "revCount": 17,
+        "rev": "68121d50b52fb56038871c97c97e7a12ffe987c2",
+        "revCount": 20,
         "type": "git",
         "url": "https://gitea.gregorlohaus.com/gregor/jlibghostty.git"
       },

src/main/java/com/gregor/jprototerm/AppConfig.java

@@ -36,9 +36,11 @@ public record AppConfig(
             "navigate_up",
             "navigate_right",
             "toggle_floating",
-            "new_floating",
-            "next_floating",
+            "new_pane",
             "close_pane",
+            "new_tab",
+            "previous_tab",
+            "next_tab",
             "open_font_selector",
             "open_scrollback"
     );
@@ -86,17 +88,19 @@ public record AppConfig(
                 true,
                 defaultScrollbackEditorCommand(),
                 Map.of(),
-                Map.of(
-                        "navigate_left", KeyBinding.parse("ALT+H"),
-                        "navigate_down", KeyBinding.parse("ALT+J"),
-                        "navigate_up", KeyBinding.parse("ALT+K"),
-                        "navigate_right", KeyBinding.parse("ALT+L"),
-                        "toggle_floating", KeyBinding.parse("ALT+F"),
-                        "new_floating", KeyBinding.parse("ALT+SHIFT+F"),
-                        "next_floating", KeyBinding.parse("ALT+F12"),
-                        "close_pane", KeyBinding.parse("ALT+X"),
-                        "open_font_selector", KeyBinding.parse("ALT+T"),
-                        "open_scrollback", KeyBinding.parse("ALT+S")
+                Map.ofEntries(
+                        Map.entry("navigate_left", KeyBinding.parse("ALT+H")),
+                        Map.entry("navigate_down", KeyBinding.parse("ALT+J")),
+                        Map.entry("navigate_up", KeyBinding.parse("ALT+K")),
+                        Map.entry("navigate_right", KeyBinding.parse("ALT+L")),
+                        Map.entry("toggle_floating", KeyBinding.parse("ALT+F")),
+                        Map.entry("new_pane", KeyBinding.parse("ALT+N")),
+                        Map.entry("close_pane", KeyBinding.parse("ALT+X")),
+                        Map.entry("new_tab", KeyBinding.parse("ALT+A")),
+                        Map.entry("previous_tab", KeyBinding.parse("ALT+SHIFT+H")),
+                        Map.entry("next_tab", KeyBinding.parse("ALT+SHIFT+L")),
+                        Map.entry("open_font_selector", KeyBinding.parse("ALT+T")),
+                        Map.entry("open_scrollback", KeyBinding.parse("ALT+S"))
                 )
         );
     }

src/main/java/com/gregor/jprototerm/Compositor.java

@@ -0,0 +1,442 @@
+package com.gregor.jprototerm;
+
+import dev.jlibghostty.KeyModifiers;
+import dev.jlibghostty.MouseButton;
+import dev.jlibghostty.MouseEncoderSize;
+import dev.jlibghostty.MouseInput;
+import javafx.geometry.Pos;
+import javafx.scene.Parent;
+import javafx.scene.control.Label;
+import javafx.scene.input.InputEvent;
+import javafx.scene.input.MouseEvent;
+import javafx.scene.input.ScrollEvent;
+import javafx.scene.input.ScrollEvent.VerticalTextScrollUnits;
+import javafx.scene.layout.Background;
+import javafx.scene.layout.BackgroundFill;
+import javafx.scene.layout.CornerRadii;
+import javafx.scene.layout.HBox;
+import javafx.scene.layout.Pane;
+import javafx.scene.paint.Color;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Owns the window's tabs and exposes the terminal surface as a JavaFX scene graph. Each
+ * terminal pane is mounted as its own node, so JavaFX child order handles stacking and clipping
+ * between panes. The pane model still owns terminals, ptys, cell geometry, and snapshots; this
+ * class handles tab/pane lifecycle, layout, focus, mouse routing, and frame scheduling.
+ */
+public final class Compositor {
+    private static final Color GAP_BACKGROUND = Color.rgb(16, 16, 18);
+    private static final Color TAB_TEXT = Color.rgb(225, 229, 235);
+    private static final Color TAB_INACTIVE_TEXT = Color.rgb(128, 136, 148);
+    private static final Color TAB_ACTIVE_BACKGROUND = Color.rgb(45, 55, 72);
+    private static final Color TAB_INACTIVE_BACKGROUND = Color.rgb(22, 24, 28);
+    private static final double TAB_BAR_HEIGHT = 22.0;
+
+    private final Pane root = new Pane();
+    private final Pane paneLayer = new Pane();
+    private final HBox tabBar = new HBox(1.0);
+    private final AppConfig config;
+    private final TerminalMetrics metrics;
+    private final List<Tab> tabs = new ArrayList<>();
+    private final Map<TerminalPane, TerminalPaneNode> nodes = new HashMap<>();
+    private int currentTabIndex;
+    private boolean sceneDirty = true;
+    private double lastWidth = -1.0;
+    private double lastHeight = -1.0;
+    private long lastContentVersion = Long.MIN_VALUE;
+    private boolean mouseButtonPressed;
+    private MouseButton pressedButton = MouseButton.UNKNOWN;
+
+    public Compositor(AppConfig config, TerminalMetrics metrics) {
+        this.config = config;
+        this.metrics = metrics;
+        tabs.add(new Tab(config, metrics));
+
+        root.setFocusTraversable(true);
+        root.setBackground(new Background(new BackgroundFill(GAP_BACKGROUND, CornerRadii.EMPTY, null)));
+        root.getChildren().setAll(paneLayer, tabBar);
+        root.setOnMousePressed(event -> root.requestFocus());
+    }
+
+    public Parent node() {
+        return root;
+    }
+
+    public void requestFocus() {
+        root.requestFocus();
+    }
+
+    public void setFont(String family, double size) {
+        metrics.setFont(family, size);
+        nodes.values().forEach(TerminalPaneNode::discard);
+        markSceneDirty();
+    }
+
+    // ---- Tabs and panes -------------------------------------------------------------
+
+    public boolean isEmpty() {
+        return tabs.isEmpty();
+    }
+
+    public TerminalPane activePane() {
+        return currentTab().activePane();
+    }
+
+    public void navigate(Direction direction) {
+        if (!isEmpty() && currentTab().navigate(direction)) {
+            markSceneDirty();
+        }
+    }
+
+    public void toggleFloating() {
+        if (isEmpty()) {
+            return;
+        }
+        currentTab().toggleFloating();
+        markSceneDirty();
+    }
+
+    public void createPane() {
+        if (isEmpty()) {
+            return;
+        }
+        currentTab().createPane();
+        markSceneDirty();
+    }
+
+    public void closeActivePane() {
+        if (isEmpty()) {
+            return;
+        }
+        currentTab().closeActivePane();
+        if (currentTab().isEmpty()) {
+            tabs.remove(currentTabIndex);
+            if (currentTabIndex >= tabs.size()) {
+                currentTabIndex = Math.max(0, tabs.size() - 1);
+            }
+        }
+        markSceneDirty();
+    }
+
+    public void newTab() {
+        tabs.add(new Tab(config, metrics));
+        currentTabIndex = tabs.size() - 1;
+        markSceneDirty();
+    }
+
+    public void nextTab() {
+        if (tabs.size() > 1) {
+            currentTabIndex = (currentTabIndex + 1) % tabs.size();
+            markSceneDirty();
+        }
+    }
+
+    public void previousTab() {
+        if (tabs.size() > 1) {
+            currentTabIndex = (currentTabIndex - 1 + tabs.size()) % tabs.size();
+            markSceneDirty();
+        }
+    }
+
+    public void close() {
+        for (Tab tab : tabs) {
+            tab.close();
+        }
+        tabs.clear();
+        nodes.clear();
+        paneLayer.getChildren().clear();
+    }
+
+    private Tab currentTab() {
+        return tabs.get(currentTabIndex);
+    }
+
+    private List<TerminalPane> currentPanes() {
+        return tabs.isEmpty() ? List.of() : currentTab().panes();
+    }
+
+    private List<TerminalPane> allOpenPanes() {
+        List<TerminalPane> panes = new ArrayList<>();
+        for (Tab tab : tabs) {
+            panes.addAll(tab.allPanes());
+        }
+        return panes;
+    }
+
+    private boolean isActive(TerminalPane pane) {
+        return !tabs.isEmpty() && currentTab().isActive(pane);
+    }
+
+    private void focus(TerminalPane pane) {
+        if (!tabs.isEmpty() && currentTab().focus(pane)) {
+            markSceneDirty();
+        }
+    }
+
+    // ---- Rendering ------------------------------------------------------------------
+
+    public void render() {
+        double width = root.getWidth();
+        double height = root.getHeight();
+        long contentVersion = tabs.isEmpty() ? 0 : currentTab().contentVersion();
+        boolean geometryChanged = width != lastWidth || height != lastHeight;
+        boolean contentChanged = contentVersion != lastContentVersion;
+        boolean syncScene = sceneDirty || geometryChanged;
+
+        if (!syncScene && !contentChanged) {
+            return;
+        }
+
+        lastWidth = width;
+        lastHeight = height;
+        lastContentVersion = contentVersion;
+        sceneDirty = false;
+        if (syncScene) {
+            syncSceneGraph(width, height);
+        }
+        renderVisiblePanes();
+    }
+
+    private void markSceneDirty() {
+        sceneDirty = true;
+    }
+
+    private void syncSceneGraph(double width, double height) {
+        double topInset = tabs.size() > 1 ? TAB_BAR_HEIGHT : 0.0;
+
+        paneLayer.resizeRelocate(0.0, 0.0, width, height);
+        updateTabBar(width, topInset);
+
+        if (!tabs.isEmpty()) {
+            currentTab().layout(width, height, topInset);
+        }
+
+        List<TerminalPane> panes = currentPanes();
+        retainNodes(allOpenPanes());
+        List<TerminalPaneNode> orderedNodes = new ArrayList<>(panes.size());
+        for (TerminalPane pane : panes) {
+            pane.fitToBounds();
+            TerminalPaneNode node = nodeFor(pane);
+            node.resizeRelocate(Math.round(pane.x()), Math.round(pane.y()), pane.width(), pane.height());
+            orderedNodes.add(node);
+        }
+        paneLayer.getChildren().setAll(orderedNodes);
+    }
+
+    private void renderVisiblePanes() {
+        for (TerminalPane pane : currentPanes()) {
+            TerminalPaneNode node = nodes.get(pane);
+            if (node != null) {
+                node.renderIncremental(isActive(pane));
+            }
+        }
+    }
+
+    private TerminalPaneNode nodeFor(TerminalPane pane) {
+        return nodes.computeIfAbsent(pane, this::createNode);
+    }
+
+    private TerminalPaneNode createNode(TerminalPane pane) {
+        TerminalPaneNode node = new TerminalPaneNode(pane, metrics);
+        node.setOnMousePressed(event -> handleMousePressed(pane, event));
+        node.setOnMouseReleased(event -> handleMouseReleased(pane, event));
+        node.setOnMouseDragged(event -> handleMouseDragged(pane, event));
+        node.setOnMouseMoved(event -> handleMouseMoved(pane, event));
+        node.setOnScroll(event -> handleScroll(pane, event));
+        return node;
+    }
+
+    private void retainNodes(List<TerminalPane> openPanes) {
+        Set<TerminalPane> open = new HashSet<>(openPanes);
+        nodes.keySet().removeIf(pane -> !open.contains(pane));
+    }
+
+    private void updateTabBar(double width, double barHeight) {
+        tabBar.setVisible(barHeight > 0.0);
+        tabBar.setManaged(false);
+        tabBar.resizeRelocate(0.0, 0.0, width, barHeight);
+        tabBar.getChildren().clear();
+        if (barHeight <= 0.0) {
+            return;
+        }
+
+        double segmentWidth = width / tabs.size();
+        for (int i = 0; i < tabs.size(); i++) {
+            Label label = new Label(Integer.toString(i + 1));
+            boolean current = i == currentTabIndex;
+            label.setAlignment(Pos.CENTER);
+            label.setTextFill(current ? TAB_TEXT : TAB_INACTIVE_TEXT);
+            label.setBackground(new Background(new BackgroundFill(
+                    current ? TAB_ACTIVE_BACKGROUND : TAB_INACTIVE_BACKGROUND,
+                    CornerRadii.EMPTY,
+                    null)));
+            label.setFont(javafx.scene.text.Font.font(metrics.fontFamily(), Math.max(9.0, Math.min(13.0, barHeight * 0.62))));
+            label.setMinSize(0.0, barHeight);
+            label.setPrefSize(Math.max(0.0, segmentWidth - 1.0), barHeight);
+            label.setMaxSize(Double.MAX_VALUE, barHeight);
+            final int index = i;
+            label.setOnMousePressed(event -> {
+                currentTabIndex = index;
+                markSceneDirty();
+                root.requestFocus();
+                event.consume();
+            });
+            tabBar.getChildren().add(label);
+        }
+    }
+
+    // ---- Input ----------------------------------------------------------------------
+
+    private void handleMousePressed(TerminalPane pane, MouseEvent event) {
+        root.requestFocus();
+        focus(pane);
+        pressedButton = mouseButton(event);
+        mouseButtonPressed = true;
+        MouseTarget target = mouseTarget(pane);
+        if (target == null) {
+            return;
+        }
+        send(pane, target, MouseInput.press(pressedButton, localX(event.getX(), target), localY(event.getY(), target), modifiers(event)), true, event);
+    }
+
+    private void handleMouseReleased(TerminalPane pane, MouseEvent event) {
+        MouseButton button = pressedButton == MouseButton.UNKNOWN ? mouseButton(event) : pressedButton;
+        MouseTarget target = mouseTarget(pane);
+        if (target != null) {
+            send(pane, target, MouseInput.release(button, localX(event.getX(), target), localY(event.getY(), target), modifiers(event)), false, event);
+        }
+        mouseButtonPressed = false;
+        pressedButton = MouseButton.UNKNOWN;
+    }
+
+    private void handleMouseDragged(TerminalPane pane, MouseEvent event) {
+        MouseButton button = pressedButton == MouseButton.UNKNOWN ? mouseButton(event) : pressedButton;
+        MouseTarget target = mouseTarget(pane);
+        if (target == null) {
+            return;
+        }
+        send(pane, target, MouseInput.drag(button, localX(event.getX(), target), localY(event.getY(), target), modifiers(event)), true, event);
+    }
+
+    private void handleMouseMoved(TerminalPane pane, MouseEvent event) {
+        MouseTarget target = mouseTarget(pane);
+        if (target == null) {
+            return;
+        }
+        send(pane, target, MouseInput.motion(localX(event.getX(), target), localY(event.getY(), target), modifiers(event)), mouseButtonPressed, event);
+    }
+
+    private void handleScroll(TerminalPane pane, ScrollEvent event) {
+        root.requestFocus();
+        focus(pane);
+        int direction = scrollDirection(event);
+        if (direction == 0) {
+            return;
+        }
+
+        MouseButton wheelButton = direction > 0 ? MouseButton.FOUR : MouseButton.FIVE;
+        int rows = scrollRows(event);
+        MouseTarget target = mouseTarget(pane);
+        boolean sent = false;
+        if (target != null) {
+            double ex = localX(event.getX(), target);
+            double ey = localY(event.getY(), target);
+            KeyModifiers modifiers = modifiers(event);
+            for (int i = 0; i < rows; i++) {
+                if (!send(pane, target, MouseInput.press(wheelButton, ex, ey, modifiers), mouseButtonPressed, event)) {
+                    break;
+                }
+                sent = true;
+            }
+        }
+        if (!sent) {
+            pane.scrollViewport(direction > 0 ? -rows : rows);
+            event.consume();
+        }
+    }
+
+    private boolean send(TerminalPane pane, MouseTarget target, MouseInput input, boolean anyButtonPressed, InputEvent event) {
+        boolean sent = pane.sendMouse(input, target.size(), anyButtonPressed);
+        if (sent) {
+            event.consume();
+        }
+        return sent;
+    }
+
+    private MouseTarget mouseTarget(TerminalPane pane) {
+        if (pane.width() <= 2 * TerminalMetrics.PADDING || pane.height() <= 2 * TerminalMetrics.PADDING) {
+            return null;
+        }
+
+        int columns = metrics.columnsFor(pane.width());
+        int rows = metrics.rowsFor(pane.height());
+        long cellWidth = Math.max(1L, Math.round(metrics.cellWidth()));
+        long cellHeight = Math.max(1L, Math.round(metrics.lineHeight()));
+        long screenWidth = Math.max(1L, Math.round(columns * metrics.cellWidth()));
+        long screenHeight = Math.max(1L, Math.round(rows * metrics.lineHeight()));
+        return new MouseTarget(MouseEncoderSize.of(screenWidth, screenHeight, cellWidth, cellHeight), screenWidth, screenHeight);
+    }
+
+    private static double localX(double nodeX, MouseTarget target) {
+        return clamp(nodeX - TerminalMetrics.PADDING, 0.0, target.screenWidth() - 1.0);
+    }
+
+    private static double localY(double nodeY, MouseTarget target) {
+        return clamp(nodeY - TerminalMetrics.PADDING, 0.0, target.screenHeight() - 1.0);
+    }
+
+    private static double clamp(double value, double min, double max) {
+        return Math.max(min, Math.min(max, value));
+    }
+
+    private static KeyModifiers modifiers(MouseEvent event) {
+        return KeyModifiers.of(event.isShiftDown(), event.isControlDown(), event.isAltDown(), event.isMetaDown());
+    }
+
+    private static KeyModifiers modifiers(ScrollEvent event) {
+        return KeyModifiers.of(event.isShiftDown(), event.isControlDown(), event.isAltDown(), event.isMetaDown());
+    }
+
+    private static int scrollRows(ScrollEvent event) {
+        double rows;
+        if (event.getTextDeltaYUnits() == VerticalTextScrollUnits.LINES && event.getTextDeltaY() != 0.0) {
+            rows = Math.abs(event.getTextDeltaY());
+        } else if (event.getTextDeltaYUnits() == VerticalTextScrollUnits.PAGES && event.getTextDeltaY() != 0.0) {
+            rows = Math.abs(event.getTextDeltaY()) * 24.0;
+        } else if (event.getMultiplierY() > 0.0) {
+            rows = Math.abs(event.getDeltaY()) / event.getMultiplierY();
+        } else {
+            rows = Math.abs(event.getDeltaY()) / 40.0;
+        }
+        return Math.max(1, Math.min(64, (int) Math.ceil(rows)));
+    }
+
+    private static int scrollDirection(ScrollEvent event) {
+        if (event.getDeltaY() != 0.0) {
+            return event.getDeltaY() > 0.0 ? 1 : -1;
+        }
+        if (event.getTextDeltaYUnits() != VerticalTextScrollUnits.NONE && event.getTextDeltaY() != 0.0) {
+            return event.getTextDeltaY() > 0.0 ? 1 : -1;
+        }
+        return 0;
+    }
+
+    private static MouseButton mouseButton(MouseEvent event) {
+        return switch (event.getButton()) {
+            case PRIMARY -> MouseButton.LEFT;
+            case SECONDARY -> MouseButton.RIGHT;
+            case MIDDLE -> MouseButton.MIDDLE;
+            default -> MouseButton.UNKNOWN;
+        };
+    }
+
+    private record MouseTarget(MouseEncoderSize size, long screenWidth, long screenHeight) {
+    }
+}

src/main/java/com/gregor/jprototerm/Main.java

@@ -2,6 +2,7 @@ package com.gregor.jprototerm;
 
 import javafx.animation.AnimationTimer;
 import javafx.application.Application;
+import javafx.application.Platform;
 import javafx.scene.Scene;
 import javafx.scene.control.ButtonType;
 import javafx.scene.control.ComboBox;
@@ -11,7 +12,6 @@ import javafx.scene.control.Spinner;
 import javafx.scene.control.SpinnerValueFactory;
 import javafx.scene.input.KeyEvent;
 import javafx.scene.layout.GridPane;
-import javafx.scene.layout.StackPane;
 import javafx.scene.text.Font;
 import javafx.stage.Stage;
 
@@ -20,65 +20,72 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 
 public final class Main extends Application {
-    private TerminalWorkspace workspace;
-    private TerminalCanvasView terminalView;
+    private Compositor compositor;
+    private TerminalMetrics metrics;
     private AppConfig config;
 
     @Override
     public void start(Stage stage) {
         config = AppConfig.load();
 
-        workspace = new TerminalWorkspace(config);
-        terminalView = new TerminalCanvasView(workspace, config);
+        metrics = new TerminalMetrics(config.fontFamily(), config.fontSize());
+        compositor = new Compositor(config, metrics);
 
-        StackPane root = new StackPane(terminalView.canvas());
-        terminalView.canvas().widthProperty().bind(root.widthProperty());
-        terminalView.canvas().heightProperty().bind(root.heightProperty());
-
-        Scene scene = new Scene(root, config.windowWidth(), config.windowHeight());
+        Scene scene = new Scene(compositor.node(), config.windowWidth(), config.windowHeight());
         scene.addEventFilter(KeyEvent.KEY_PRESSED, this::handlePressed);
         scene.addEventFilter(KeyEvent.KEY_TYPED, event -> handleTyped(event));
 
         new AnimationTimer() {
             @Override
             public void handle(long now) {
-                terminalView.render();
+                compositor.render();
             }
         }.start();
 
         stage.setTitle("jprototerm");
         stage.setScene(scene);
         stage.setOnCloseRequest(event -> {
-            workspace.close();
+            compositor.close();
         });
         stage.show();
-        terminalView.canvas().requestFocus();
+        compositor.requestFocus();
     }
 
     private void handlePressed(KeyEvent event) {
         if (config.keybindings().get("navigate_left").matches(event)) {
-            workspace.navigate(Direction.LEFT);
+            compositor.navigate(Direction.LEFT);
             event.consume();
         } else if (config.keybindings().get("navigate_down").matches(event)) {
-            workspace.navigate(Direction.DOWN);
+            compositor.navigate(Direction.DOWN);
             event.consume();
         } else if (config.keybindings().get("navigate_up").matches(event)) {
-            workspace.navigate(Direction.UP);
+            compositor.navigate(Direction.UP);
             event.consume();
         } else if (config.keybindings().get("navigate_right").matches(event)) {
-            workspace.navigate(Direction.RIGHT);
+            compositor.navigate(Direction.RIGHT);
             event.consume();
         } else if (config.keybindings().get("toggle_floating").matches(event)) {
-            workspace.toggleFloating();
+            compositor.toggleFloating();
             event.consume();
-        } else if (config.keybindings().get("new_floating").matches(event)) {
-            workspace.createFloatingPane();
-            event.consume();
-        } else if (config.keybindings().get("next_floating").matches(event)) {
-            workspace.nextFloatingPane();
+        } else if (config.keybindings().get("new_pane").matches(event)) {
+            compositor.createPane();
             event.consume();
         } else if (config.keybindings().get("close_pane").matches(event)) {
-            workspace.closeActivePane();
+            compositor.closeActivePane();
+            event.consume();
+            if (compositor.isEmpty()) {
+                // Closing the last pane quits the app.
+                compositor.close();
+                Platform.exit();
+            }
+        } else if (config.keybindings().get("new_tab").matches(event)) {
+            compositor.newTab();
+            event.consume();
+        } else if (config.keybindings().get("previous_tab").matches(event)) {
+            compositor.previousTab();
+            event.consume();
+        } else if (config.keybindings().get("next_tab").matches(event)) {
+            compositor.nextTab();
             event.consume();
         } else if (config.keybindings().get("open_font_selector").matches(event)) {
             openFontSelector();
@@ -89,7 +96,7 @@ public final class Main extends Application {
         } else {
             String encoded = KeyEncoder.encode(event);
             if (encoded != null) {
-                workspace.activePane().send(encoded);
+                compositor.activePane().send(encoded);
                 event.consume();
             }
         }
@@ -102,7 +109,7 @@ public final class Main extends Application {
 
         String text = event.getCharacter();
         if (text != null && !text.isEmpty() && text.charAt(0) >= 0x20 && text.charAt(0) != 0x7f) {
-            workspace.activePane().send(text);
+            compositor.activePane().send(text);
             event.consume();
         }
     }
@@ -145,18 +152,18 @@ public final class Main extends Application {
                     double selectedSize = size.getValue();
                     config = config.withFont(selectedFamily.trim(), selectedSize);
                     config.save();
-                    terminalView.setFont(config.fontFamily(), config.fontSize());
-                    terminalView.canvas().requestFocus();
+                    compositor.setFont(config.fontFamily(), config.fontSize());
+                    compositor.requestFocus();
                 });
     }
 
     private void openScrollbackInEditor() {
         try {
             Path file = Files.createTempFile("jprototerm-scrollback-", ".txt");
-            Files.writeString(file, workspace.activePane().scrollbackText());
+            Files.writeString(file, compositor.activePane().scrollbackText());
             file.toFile().deleteOnExit();
 
-            workspace.activePane().send(scrollbackEditorCommand(file) + "\r");
+            compositor.activePane().send(scrollbackEditorCommand(file) + "\r");
         } catch (IOException ex) {
             System.err.println("Could not open scrollback in editor: " + ex.getMessage());
         }

src/main/java/com/gregor/jprototerm/ShellSession.java

@@ -1,7 +1,5 @@
 package com.gregor.jprototerm;
 
-import javafx.application.Platform;
-
 import java.nio.charset.StandardCharsets;
 import java.util.HashMap;
 import java.util.Map;
@@ -94,23 +92,25 @@ public final class ShellSession implements AutoCloseable {
     }
 
     private void readOutput(TerminalPane pane) {
-        byte[] buffer = new byte[8192];
+        byte[] buffer = new byte[65536];
         try {
             int read;
             while ((read = pty.read(buffer)) != -1) {
-                if (!closed) {
+                if (closed) {
+                    break;
+                }
                 byte[] bytes = new byte[read];
                 System.arraycopy(buffer, 0, bytes, 0, read);
-                    Platform.runLater(() -> {
-                        if (!closed) {
+                // Feed the terminal model straight from the reader thread. terminal access is
+                // guarded by the per-terminal lock, and the render loop picks the change up on
+                // the next pulse. Avoiding a Platform.runLater hop per chunk removes a frame of
+                // latency and stops write tasks from contending with rendering on the FX thread
+                // when a TUI repaints heavily (the input-lag culprit).
                 pane.write(bytes);
             }
-                    });
-                }
-            }
         } catch (RuntimeException ex) {
             if (!closed) {
-                Platform.runLater(() -> pane.write("\r\nshell output stopped: " + ex.getMessage() + "\r\n"));
+                pane.write("\r\nshell output stopped: " + ex.getMessage() + "\r\n");
             }
         }
     }

src/main/java/com/gregor/jprototerm/Tab.java

@@ -0,0 +1,288 @@
+package com.gregor.jprototerm;
+
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.stream.Stream;
+
+/**
+ * One tab: a row of tiled panes with a group of floating panes shown over them. Floating panes
+ * are shown/hidden as a group ({@code floatingVisible}), and there is always at least one tiled
+ * pane — a floating pane is promoted if the last tiled one closes — so the layout always has a
+ * base. The {@link Compositor} owns the tabs and renders only the current one; mutating methods
+ * return whether they actually changed anything so it can bump its layout version.
+ */
+final class Tab implements AutoCloseable {
+    private final AppConfig config;
+    private final TerminalMetrics metrics;
+    private final List<TerminalPane> tiled = new ArrayList<>();
+    private final List<TerminalPane> floating = new ArrayList<>();
+    private boolean floatingVisible;
+    private TerminalPane active;
+    // The floating pane to re-focus when the group is shown again, and to prefer when promoting
+    // after the last tiled pane closes.
+    private TerminalPane lastFocusedFloating;
+    // Last laid-out size, so a newly opened pane can be created at roughly its eventual rect
+    // (and thus grid). Seeded from the configured window size for the first pane, which is
+    // opened before any layout pass runs.
+    private double lastWidth;
+    private double lastHeight;
+    private double lastTopInset;
+    // Bumped whenever one of this tab's panes changes content; the compositor reads the current
+    // tab's value each frame as an O(1) "anything to repaint?" check.
+    private long contentVersion;
+
+    Tab(AppConfig config, TerminalMetrics metrics) {
+        this.config = config;
+        this.metrics = metrics;
+        this.lastWidth = config.windowWidth();
+        this.lastHeight = config.windowHeight();
+        TerminalPane first = openPane(false);
+        tiled.add(first);
+        active = first;
+    }
+
+    TerminalPane activePane() {
+        return active;
+    }
+
+    boolean isEmpty() {
+        return tiled.isEmpty() && floating.isEmpty();
+    }
+
+    long contentVersion() {
+        return contentVersion;
+    }
+
+    /**
+     * Panes to composite, bottom-to-top: tiled first, then (when shown) the floating group with
+     * the active floating pane on top.
+     */
+    List<TerminalPane> panes() {
+        if (!floatingVisible || floating.isEmpty()) {
+            return List.copyOf(tiled);
+        }
+        List<TerminalPane> ordered = new ArrayList<>(tiled.size() + floating.size());
+        ordered.addAll(tiled);
+        for (TerminalPane pane : floating) {
+            if (pane != active) {
+                ordered.add(pane);
+            }
+        }
+        if (floating.contains(active)) {
+            ordered.add(active); // active floating pane on top
+        }
+        return List.copyOf(ordered);
+    }
+
+    List<TerminalPane> allPanes() {
+        List<TerminalPane> all = new ArrayList<>(tiled.size() + floating.size());
+        all.addAll(tiled);
+        all.addAll(floating);
+        return List.copyOf(all);
+    }
+
+    boolean isActive(TerminalPane pane) {
+        return pane != null && pane == active;
+    }
+
+    boolean focus(TerminalPane pane) {
+        if (pane == active || !isFocusable(pane)) {
+            return false;
+        }
+        setActive(pane);
+        return true;
+    }
+
+    void layout(double width, double height, double topInset) {
+        this.lastWidth = width;
+        this.lastHeight = height;
+        this.lastTopInset = topInset;
+        double availHeight = height - topInset;
+
+        double tileWidth = width / Math.max(1, tiled.size());
+        for (int i = 0; i < tiled.size(); i++) {
+            tiled.get(i).bounds(i * tileWidth, topInset, tileWidth, availHeight);
+        }
+
+        double floatingWidth = Math.max(420, width * 0.58);
+        double floatingHeight = Math.max(260, availHeight * 0.58);
+        for (int i = 0; i < floating.size(); i++) {
+            double offset = i * 28.0;
+            floating.get(i).bounds(
+                    Math.min(width - floatingWidth - 12.0, ((width - floatingWidth) / 2.0) + offset),
+                    Math.min(height - floatingHeight - 12.0, topInset + ((availHeight - floatingHeight) / 2.0) + offset),
+                    floatingWidth,
+                    floatingHeight);
+        }
+    }
+
+    boolean navigate(Direction direction) {
+        if (floating.contains(active) && navigateFloatingStack(direction)) {
+            return true;
+        }
+        TerminalPane target = focusable()
+                .filter(pane -> pane != active)
+                .filter(pane -> directionFilter(direction, active, pane))
+                .min(Comparator.comparingDouble(pane -> distance(active, pane)))
+                .orElse(null);
+        if (target != null) {
+            setActive(target);
+            return true;
+        }
+        return false;
+    }
+
+    void toggleFloating() {
+        if (floating.isEmpty()) {
+            createFloatingPane();
+            return;
+        }
+        if (floatingVisible) {
+            floatingVisible = false;
+            if (floating.contains(active)) {
+                setActive(tiled.get(0));
+            }
+        } else {
+            floatingVisible = true;
+            setActive(floating.contains(lastFocusedFloating) ? lastFocusedFloating : floating.get(floating.size() - 1));
+        }
+    }
+
+    /** Adds a floating pane while the floating group is shown, otherwise a tiled pane. */
+    void createPane() {
+        if (floatingVisible) {
+            createFloatingPane();
+        } else {
+            TerminalPane pane = openPane(false);
+            tiled.add(pane);
+            setActive(pane);
+        }
+    }
+
+    void closeActivePane() {
+        TerminalPane closing = active;
+        boolean wasFloating = floating.remove(closing);
+        if (!wasFloating) {
+            tiled.remove(closing);
+        }
+        if (closing == lastFocusedFloating) {
+            lastFocusedFloating = null;
+        }
+        closing.close();
+
+        if (tiled.isEmpty() && floating.isEmpty()) {
+            active = null; // tab is now empty; the compositor drops it
+            return;
+        }
+
+        // Always keep a tiled base: if the last tiled pane just closed, promote a floating one
+        // (preferring the last focused).
+        if (tiled.isEmpty()) {
+            TerminalPane promote = floating.contains(lastFocusedFloating) ? lastFocusedFloating : floating.get(0);
+            var promoteIndex = floating.indexOf(promote);
+            var nextFocussed = promoteIndex == 0 ? 0 : promoteIndex - 1;
+            floating.remove(promote);
+            tiled.add(promote);
+            if (promote == lastFocusedFloating) {
+                lastFocusedFloating = null;
+                if (!floating.isEmpty()) {
+                    lastFocusedFloating = floating.isEmpty() ? null : floating.get(nextFocussed);
+                }
+            }
+        }
+        if (floating.isEmpty()) {
+            floatingVisible = false;
+        }
+
+        setActive(wasFloating && floatingVisible ? floating.get(floating.size() - 1) : tiled.get(0));
+    }
+
+    private void setActive(TerminalPane pane) {
+        active = pane;
+        if (floating.contains(pane)) {
+            lastFocusedFloating = pane;
+        }
+    }
+
+    private void createFloatingPane() {
+        TerminalPane pane = openPane(true);
+        floating.add(pane);
+        floatingVisible = true;
+        setActive(pane);
+    }
+
+    private boolean navigateFloatingStack(Direction direction) {
+        if (floating.size() < 2) {
+            return false;
+        }
+        int current = floating.indexOf(active);
+        if (current < 0) {
+            return false;
+        }
+        int next = switch (direction) {
+            case LEFT, UP -> current - 1;
+            case DOWN, RIGHT -> current + 1;
+        };
+        if (next < 0 || next >= floating.size()) {
+            return false;
+        }
+        setActive(floating.get(next));
+        return true;
+    }
+
+    private boolean isFocusable(TerminalPane pane) {
+        return tiled.contains(pane) || (floatingVisible && floating.contains(pane));
+    }
+
+    private Stream<TerminalPane> focusable() {
+        return floatingVisible ? Stream.concat(tiled.stream(), floating.stream()) : tiled.stream();
+    }
+
+    private void markContentChanged() {
+        contentVersion++;
+    }
+
+    private TerminalPane openPane(boolean asFloating) {
+        double availHeight = lastHeight - lastTopInset;
+        double widthPx;
+        double heightPx;
+        if (asFloating) {
+            widthPx = Math.max(420, lastWidth * 0.58);
+            heightPx = Math.max(260, availHeight * 0.58);
+        } else {
+            // A new tiled pane joins the row, so each gets 1/(n+1) of the width.
+            widthPx = lastWidth / (tiled.size() + 1);
+            heightPx = availHeight;
+        }
+        return TerminalPane.create(config, metrics, this::markContentChanged, widthPx, heightPx);
+    }
+
+    private static boolean directionFilter(Direction direction, TerminalPane current, TerminalPane candidate) {
+        double currentCenterX = current.x() + current.width() / 2.0;
+        double currentCenterY = current.y() + current.height() / 2.0;
+        double candidateCenterX = candidate.x() + candidate.width() / 2.0;
+        double candidateCenterY = candidate.y() + candidate.height() / 2.0;
+
+        return switch (direction) {
+            case LEFT -> candidateCenterX < currentCenterX;
+            case DOWN -> candidateCenterY > currentCenterY;
+            case UP -> candidateCenterY < currentCenterY;
+            case RIGHT -> candidateCenterX > currentCenterX;
+        };
+    }
+
+    private static double distance(TerminalPane current, TerminalPane candidate) {
+        double dx = (current.x() + current.width() / 2.0) - (candidate.x() + candidate.width() / 2.0);
+        double dy = (current.y() + current.height() / 2.0) - (candidate.y() + candidate.height() / 2.0);
+        return Math.sqrt(dx * dx + dy * dy);
+    }
+
+    @Override
+    public void close() {
+        tiled.forEach(TerminalPane::close);
+        floating.forEach(TerminalPane::close);
+        tiled.clear();
+        floating.clear();
+    }
+}

src/main/java/com/gregor/jprototerm/TerminalCanvasView.java

@@ -1,799 +0,0 @@
-package com.gregor.jprototerm;
-
-import dev.jlibghostty.KittyImageCompression;
-import dev.jlibghostty.KittyImageFormat;
-import dev.jlibghostty.KittyImageSnapshot;
-import dev.jlibghostty.KittyPlacement;
-import dev.jlibghostty.KittyPlacementLayer;
-import dev.jlibghostty.KittyPlaceholder;
-import dev.jlibghostty.KittyRenderInfo;
-import dev.jlibghostty.KeyModifiers;
-import dev.jlibghostty.MouseButton;
-import dev.jlibghostty.MouseEncoderSize;
-import dev.jlibghostty.MouseInput;
-import dev.jlibghostty.RenderCell;
-import dev.jlibghostty.RenderColor;
-import dev.jlibghostty.RenderCursorStyle;
-import dev.jlibghostty.RenderRow;
-import dev.jlibghostty.RenderStateSnapshot;
-import javafx.scene.canvas.Canvas;
-import javafx.scene.canvas.GraphicsContext;
-import javafx.scene.image.Image;
-import javafx.scene.image.PixelFormat;
-import javafx.scene.image.WritableImage;
-import javafx.scene.input.InputEvent;
-import javafx.scene.input.MouseEvent;
-import javafx.scene.input.ScrollEvent;
-import javafx.scene.input.ScrollEvent.VerticalTextScrollUnits;
-import javafx.scene.paint.Color;
-import javafx.scene.text.Font;
-import javafx.scene.text.FontSmoothingType;
-import javafx.scene.text.Text;
-
-import java.io.ByteArrayInputStream;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-
-public final class TerminalCanvasView {
-    private static final Color DEFAULT_FOREGROUND = Color.rgb(225, 229, 235);
-    private static final Color SELECTED_BACKGROUND = Color.rgb(52, 92, 140);
-
-    private final Canvas canvas = new Canvas();
-    private final TerminalWorkspace workspace;
-    private final AppConfig config;
-    private final Map<KittyImageKey, Image> kittyImageCache = new HashMap<>();
-    private final Map<TerminalPane, PaneRenderCache> paneRenderCache = new HashMap<>();
-    private String fontFamily;
-    private double fontSize;
-    private Font cachedFont;
-    private FontMetrics cachedMetrics;
-    private String cachedFontFamily;
-    private double cachedFontSize;
-    private String lastRenderKey;
-    private boolean mouseButtonPressed;
-    private MouseButton pressedButton = MouseButton.UNKNOWN;
-
-    public TerminalCanvasView(TerminalWorkspace workspace, AppConfig config) {
-        this.workspace = workspace;
-        this.config = config;
-        this.fontFamily = config.fontFamily();
-        this.fontSize = config.fontSize();
-        canvas.setFocusTraversable(true);
-        canvas.setOnMousePressed(this::handleMousePressed);
-        canvas.setOnMouseReleased(this::handleMouseReleased);
-        canvas.setOnMouseDragged(this::handleMouseDragged);
-        canvas.setOnMouseMoved(this::handleMouseMoved);
-        canvas.setOnScroll(this::handleScroll);
-    }
-
-    public Canvas canvas() {
-        return canvas;
-    }
-
-    public void setFont(String family, double size) {
-        this.fontFamily = family;
-        this.fontSize = size;
-        cachedFont = null;
-        cachedMetrics = null;
-        paneRenderCache.clear();
-        lastRenderKey = null;
-    }
-
-    public void render() {
-        double width = canvas.getWidth();
-        double height = canvas.getHeight();
-        workspace.layout(width, height);
-        Font font = currentFont();
-        FontMetrics metrics = currentFontMetrics();
-        List<TerminalPane> panes = workspace.panes();
-
-        String renderKey = renderKey(width, height, metrics, panes);
-        if (renderKey.equals(lastRenderKey)) {
-            return;
-        }
-        lastRenderKey = renderKey;
-
-        GraphicsContext gc = canvas.getGraphicsContext2D();
-        gc.setFill(Color.rgb(16, 16, 18));
-        gc.fillRect(0, 0, width, height);
-        gc.setFontSmoothingType(FontSmoothingType.LCD);
-
-        paneRenderCache.keySet().removeIf(pane -> !panes.contains(pane));
-        for (TerminalPane pane : panes) {
-            drawPane(gc, pane, font, metrics);
-        }
-    }
-
-    private void drawPane(GraphicsContext gc, TerminalPane pane, Font font, FontMetrics metrics) {
-        if (config.kittyGraphics() && paneHasKittyGraphics(pane)) {
-            paneRenderCache.remove(pane);
-            gc.save();
-            gc.beginPath();
-            gc.rect(pane.x(), pane.y(), pane.width(), pane.height());
-            gc.clip();
-            drawPaneContent(gc, pane, font, metrics, pane.x(), pane.y(), pane.width(), pane.height(), false);
-            gc.restore();
-            return;
-        }
-
-        PaneRenderCache cache = paneRenderCache.computeIfAbsent(pane, ignored -> new PaneRenderCache());
-        String cacheKey = paneCacheKey(pane, metrics);
-        int imageWidth = Math.max(1, (int) Math.ceil(pane.width()));
-        int imageHeight = Math.max(1, (int) Math.ceil(pane.height()));
-
-        // Allocate the offscreen buffers only when the pane size changes. Reallocating a
-        // full-pane Canvas + WritableImage on every content change churns ~20 MB per frame,
-        // which the native image's serial GC turns into Full-GC frame drops.
-        if (cache.canvas == null || cache.image == null || cache.imageWidth != imageWidth || cache.imageHeight != imageHeight) {
-            cache.canvas = new Canvas(imageWidth, imageHeight);
-            cache.image = new WritableImage(imageWidth, imageHeight);
-            cache.imageWidth = imageWidth;
-            cache.imageHeight = imageHeight;
-            cache.key = null;
-        }
-
-        // Redraw and re-snapshot into the existing buffers only when content changed.
-        if (!cacheKey.equals(cache.key)) {
-            GraphicsContext cacheGc = cache.canvas.getGraphicsContext2D();
-            cacheGc.clearRect(0, 0, imageWidth, imageHeight);
-            drawPaneContent(cacheGc, pane, font, metrics, 0.0, 0.0, imageWidth, imageHeight, true);
-            cache.canvas.snapshot(null, cache.image);
-            cache.key = cacheKey;
-        }
-
-        gc.drawImage(cache.image, pane.x(), pane.y());
-    }
-
-    private void drawPaneContent(
-            GraphicsContext gc,
-            TerminalPane pane,
-            Font font,
-            FontMetrics metrics,
-            double x,
-            double y,
-            double width,
-            double height,
-            boolean clear
-    ) {
-        if (clear) {
-            gc.clearRect(x, y, width, height);
-        }
-        gc.setFontSmoothingType(FontSmoothingType.LCD);
-        if (pane.floating()) {
-            gc.setGlobalAlpha(0.96);
-        }
-        gc.setFill(Color.rgb(9, 10, 12));
-        gc.fillRect(x, y, width, height);
-        gc.setGlobalAlpha(1.0);
-
-        gc.setStroke(workspace.isActive(pane) ? Color.rgb(87, 166, 255) : Color.rgb(52, 57, 65));
-        gc.setLineWidth(workspace.isActive(pane) ? 2.0 : 1.0);
-        gc.strokeRect(x + 0.5, y + 0.5, width - 1.0, height - 1.0);
-
-        gc.setFont(font);
-
-        int columns = Math.max(1, (int) ((width - 24.0) / metrics.cellWidth));
-        int rows = Math.max(1, (int) ((height - 24.0) / metrics.lineHeight));
-        pane.resize(columns, rows, (int) Math.round(metrics.cellWidth), (int) Math.round(metrics.lineHeight));
-
-        double left = x + 12.0;
-        double top = y + 12.0;
-        double baseline = top + metrics.baselineOffset;
-
-        RenderStateSnapshot snapshot = pane.renderSnapshot();
-        Map<KittyPlaceholderKey, KittyPlaceholderBounds> placeholderBounds = config.kittyGraphics()
-                ? kittyPlaceholderBounds(snapshot)
-                : Map.of();
-
-        if (config.kittyGraphics()) {
-            drawKittyGraphics(gc, pane, KittyPlacementLayer.BELOW_TEXT, placeholderBounds, left, top, metrics.cellWidth, metrics.lineHeight);
-        }
-
-        if (snapshot != null) {
-            for (RenderRow row : snapshot.renderRows()) {
-                drawRow(gc, row, left, top, baseline, metrics.cellWidth, metrics.lineHeight);
-            }
-        }
-
-        if (snapshot != null) {
-            drawCursor(gc, snapshot, left, top, metrics.cellWidth, metrics.lineHeight);
-        }
-
-        if (config.kittyGraphics()) {
-            drawKittyGraphics(gc, pane, KittyPlacementLayer.ABOVE_TEXT, placeholderBounds, left, top, metrics.cellWidth, metrics.lineHeight);
-        }
-    }
-
-    private static FontMetrics measureFontMetrics(Font font) {
-        Text text = new Text("┃MgÅjy");
-        text.setFont(font);
-        double lineHeight = Math.max(1.0, text.getLayoutBounds().getHeight());
-        double baselineOffset = -text.getLayoutBounds().getMinY();
-
-        Text cell = new Text("M");
-        cell.setFont(font);
-        double cellWidth = Math.max(1.0, cell.getLayoutBounds().getWidth());
-        return new FontMetrics(cellWidth, lineHeight, baselineOffset);
-    }
-
-    private Font currentFont() {
-        if (cachedFont == null || !fontFamily.equals(cachedFontFamily) || fontSize != cachedFontSize) {
-            cachedFont = Font.font(fontFamily, fontSize);
-            cachedMetrics = null;
-            cachedFontFamily = fontFamily;
-            cachedFontSize = fontSize;
-        }
-        return cachedFont;
-    }
-
-    private FontMetrics currentFontMetrics() {
-        if (cachedMetrics == null) {
-            cachedMetrics = measureFontMetrics(currentFont());
-        }
-        return cachedMetrics;
-    }
-
-    private String renderKey(double width, double height, FontMetrics metrics, List<TerminalPane> panes) {
-        StringBuilder builder = new StringBuilder();
-        builder.append(width).append(':')
-                .append(height).append(':')
-                .append(workspace.version()).append(':')
-                .append(fontFamily).append(':')
-                .append(fontSize).append(':')
-                .append(metrics.cellWidth).append(':')
-                .append(metrics.lineHeight);
-        for (TerminalPane pane : panes) {
-            builder.append('|')
-                    .append(System.identityHashCode(pane)).append(',')
-                    .append(pane.renderVersion()).append(',')
-                    .append(workspace.isActive(pane)).append(',')
-                    .append(pane.x()).append(',')
-                    .append(pane.y()).append(',')
-                    .append(pane.width()).append(',')
-                    .append(pane.height());
-        }
-        return builder.toString();
-    }
-
-    private String paneCacheKey(TerminalPane pane, FontMetrics metrics) {
-        return pane.renderVersion()
-                + ":" + workspace.isActive(pane)
-                + ":" + pane.width()
-                + ":" + pane.height()
-                + ":" + fontFamily
-                + ":" + fontSize
-                + ":" + metrics.cellWidth
-                + ":" + metrics.lineHeight
-                + ":" + config.kittyGraphics();
-    }
-
-    private static Map<KittyPlaceholderKey, KittyPlaceholderBounds> kittyPlaceholderBounds(RenderStateSnapshot snapshot) {
-        if (snapshot == null) {
-            return Map.of();
-        }
-
-        Map<KittyPlaceholderKey, KittyPlaceholderBounds> result = new HashMap<>();
-        for (RenderRow row : snapshot.renderRows()) {
-            for (RenderCell cell : row.cells()) {
-                cell.kittyPlaceholder().ifPresent(placeholder -> {
-                    KittyPlaceholderKey key = new KittyPlaceholderKey(placeholder.imageId(), placeholder.placementId());
-                    result.computeIfAbsent(key, ignored -> new KittyPlaceholderBounds()).include(row.row(), cell.column(), placeholder);
-                });
-            }
-        }
-        return result;
-    }
-
-    private void handleMousePressed(MouseEvent event) {
-        canvas.requestFocus();
-        TerminalPane pane = paneAt(event.getX(), event.getY());
-        if (pane == null) {
-            return;
-        }
-
-        workspace.focus(pane);
-        pressedButton = mouseButton(event);
-        mouseButtonPressed = true;
-        sendMouse(pane, MouseInput.press(pressedButton, eventX(pane, event.getX()), eventY(pane, event.getY()), modifiers(event)), true, event);
-    }
-
-    private void handleMouseReleased(MouseEvent event) {
-        TerminalPane pane = paneAt(event.getX(), event.getY());
-        if (pane == null) {
-            pane = workspace.activePane();
-        }
-
-        MouseButton button = pressedButton == MouseButton.UNKNOWN ? mouseButton(event) : pressedButton;
-        sendMouse(pane, MouseInput.release(button, eventX(pane, event.getX()), eventY(pane, event.getY()), modifiers(event)), false, event);
-        mouseButtonPressed = false;
-        pressedButton = MouseButton.UNKNOWN;
-    }
-
-    private void handleMouseDragged(MouseEvent event) {
-        TerminalPane pane = paneAt(event.getX(), event.getY());
-        if (pane == null) {
-            pane = workspace.activePane();
-        }
-
-        MouseButton button = pressedButton == MouseButton.UNKNOWN ? mouseButton(event) : pressedButton;
-        sendMouse(pane, MouseInput.drag(button, eventX(pane, event.getX()), eventY(pane, event.getY()), modifiers(event)), true, event);
-    }
-
-    private void handleMouseMoved(MouseEvent event) {
-        TerminalPane pane = paneAt(event.getX(), event.getY());
-        if (pane == null) {
-            return;
-        }
-
-        sendMouse(pane, MouseInput.motion(eventX(pane, event.getX()), eventY(pane, event.getY()), modifiers(event)), mouseButtonPressed, event);
-    }
-
-    private void handleScroll(ScrollEvent event) {
-        TerminalPane pane = paneAt(event.getX(), event.getY());
-        if (pane == null) {
-            return;
-        }
-
-        canvas.requestFocus();
-        workspace.focus(pane);
-        int direction = scrollDirection(event);
-        if (direction == 0) {
-            return;
-        }
-
-        MouseButton wheelButton = direction > 0 ? MouseButton.FOUR : MouseButton.FIVE;
-        int rows = scrollRows(event);
-        boolean sent = false;
-        for (int i = 0; i < rows; i++) {
-            sent |= sendMouse(
-                    pane,
-                    MouseInput.press(wheelButton, eventX(pane, event.getX()), eventY(pane, event.getY()), modifiers(event)),
-                    mouseButtonPressed,
-                    event
-            );
-        }
-        if (!sent) {
-            pane.scrollViewport(direction > 0 ? -rows : rows);
-            event.consume();
-        }
-    }
-
-    private boolean sendMouse(TerminalPane pane, MouseInput input, boolean anyButtonPressed, InputEvent event) {
-        MouseTarget target = mouseTarget(pane);
-        if (target == null) {
-            return false;
-        }
-
-        boolean sent = pane.sendMouse(input, target.size(), anyButtonPressed);
-        if (sent) {
-            event.consume();
-        }
-        return sent;
-    }
-
-    private TerminalPane paneAt(double x, double y) {
-        java.util.List<TerminalPane> panes = workspace.panes();
-        for (int i = panes.size() - 1; i >= 0; i--) {
-            TerminalPane pane = panes.get(i);
-            if (x >= pane.x() && x < pane.x() + pane.width() && y >= pane.y() && y < pane.y() + pane.height()) {
-                return pane;
-            }
-        }
-        return null;
-    }
-
-    private MouseTarget mouseTarget(TerminalPane pane) {
-        if (pane.width() <= 24.0 || pane.height() <= 24.0) {
-            return null;
-        }
-
-        FontMetrics metrics = currentFontMetrics();
-        int columns = Math.max(1, (int) ((pane.width() - 24.0) / metrics.cellWidth));
-        int rows = Math.max(1, (int) ((pane.height() - 24.0) / metrics.lineHeight));
-        long cellWidth = Math.max(1L, Math.round(metrics.cellWidth));
-        long cellHeight = Math.max(1L, Math.round(metrics.lineHeight));
-        long screenWidth = Math.max(1L, Math.round(columns * metrics.cellWidth));
-        long screenHeight = Math.max(1L, Math.round(rows * metrics.lineHeight));
-        return new MouseTarget(MouseEncoderSize.of(screenWidth, screenHeight, cellWidth, cellHeight), screenWidth, screenHeight);
-    }
-
-    private double eventX(TerminalPane pane, double canvasX) {
-        MouseTarget target = mouseTarget(pane);
-        if (target == null) {
-            return 0.0;
-        }
-        return clamp(canvasX - pane.x() - 12.0, 0.0, target.screenWidth() - 1.0);
-    }
-
-    private double eventY(TerminalPane pane, double canvasY) {
-        MouseTarget target = mouseTarget(pane);
-        if (target == null) {
-            return 0.0;
-        }
-        return clamp(canvasY - pane.y() - 12.0, 0.0, target.screenHeight() - 1.0);
-    }
-
-    private static double clamp(double value, double min, double max) {
-        return Math.max(min, Math.min(max, value));
-    }
-
-    private static KeyModifiers modifiers(MouseEvent event) {
-        return KeyModifiers.of(event.isShiftDown(), event.isControlDown(), event.isAltDown(), event.isMetaDown());
-    }
-
-    private static KeyModifiers modifiers(ScrollEvent event) {
-        return KeyModifiers.of(event.isShiftDown(), event.isControlDown(), event.isAltDown(), event.isMetaDown());
-    }
-
-    private static int scrollRows(ScrollEvent event) {
-        double rows;
-        if (event.getTextDeltaYUnits() == VerticalTextScrollUnits.LINES && event.getTextDeltaY() != 0.0) {
-            rows = Math.abs(event.getTextDeltaY());
-        } else if (event.getTextDeltaYUnits() == VerticalTextScrollUnits.PAGES && event.getTextDeltaY() != 0.0) {
-            rows = Math.abs(event.getTextDeltaY()) * 24.0;
-        } else if (event.getMultiplierY() > 0.0) {
-            rows = Math.abs(event.getDeltaY()) / event.getMultiplierY();
-        } else {
-            rows = Math.abs(event.getDeltaY()) / 40.0;
-        }
-        return Math.max(1, Math.min(64, (int) Math.ceil(rows)));
-    }
-
-    private static int scrollDirection(ScrollEvent event) {
-        if (event.getDeltaY() != 0.0) {
-            return event.getDeltaY() > 0.0 ? 1 : -1;
-        }
-        if (event.getTextDeltaYUnits() != VerticalTextScrollUnits.NONE && event.getTextDeltaY() != 0.0) {
-            return event.getTextDeltaY() > 0.0 ? 1 : -1;
-        }
-        return 0;
-    }
-
-    private static MouseButton mouseButton(MouseEvent event) {
-        return switch (event.getButton()) {
-            case PRIMARY -> MouseButton.LEFT;
-            case SECONDARY -> MouseButton.RIGHT;
-            case MIDDLE -> MouseButton.MIDDLE;
-            default -> MouseButton.UNKNOWN;
-        };
-    }
-
-    private static void drawRow(
-            GraphicsContext gc,
-            RenderRow row,
-            double left,
-            double top,
-            double baseline,
-            double cellWidth,
-            double lineHeight
-    ) {
-        for (RenderCell cell : row.cells()) {
-            if (cell.kittyPlaceholder().isPresent()) {
-                continue;
-            }
-
-            double x = left + (cell.column() * cellWidth);
-            double cellTop = top + (row.row() * lineHeight);
-            cell.background().ifPresent(background -> {
-                gc.setFill(toFxColor(background));
-                gc.fillRect(x, cellTop, cellWidth, lineHeight);
-            });
-            if (cell.selected()) {
-                gc.setFill(SELECTED_BACKGROUND);
-                gc.fillRect(x, cellTop, cellWidth, lineHeight);
-            }
-            if (cell.codepoints().length == 0) {
-                continue;
-            }
-
-            double y = baseline + (row.row() * lineHeight);
-            Color foreground = cell.foreground().map(TerminalCanvasView::toFxColor).orElse(DEFAULT_FOREGROUND);
-            gc.setFill(foreground);
-            gc.fillText(cell.text(), x, y);
-        }
-    }
-
-    private static Color toFxColor(RenderColor color) {
-        return Color.rgb(color.red(), color.green(), color.blue());
-    }
-
-    private static void drawCursor(GraphicsContext gc, RenderStateSnapshot snapshot, double left, double top, double cellWidth, double lineHeight) {
-        if (!snapshot.cursorVisible() || !snapshot.cursorViewportHasValue()) {
-            return;
-        }
-
-        double x = left + (snapshot.cursorViewportX() * cellWidth);
-        double y = top + (snapshot.cursorViewportY() * lineHeight);
-        gc.setStroke(Color.rgb(225, 229, 235));
-        gc.setFill(Color.rgb(225, 229, 235, 0.28));
-        gc.setLineWidth(1.5);
-
-        RenderCursorStyle style = snapshot.cursorStyle();
-        if (style == RenderCursorStyle.BAR) {
-            gc.strokeLine(x + 0.5, y + 2.0, x + 0.5, y + lineHeight - 2.0);
-        } else if (style == RenderCursorStyle.UNDERLINE) {
-            gc.strokeLine(x + 1.0, y + lineHeight - 2.0, x + cellWidth - 1.0, y + lineHeight - 2.0);
-        } else if (style == RenderCursorStyle.BLOCK) {
-            gc.fillRect(x + 0.5, y + 1.0, Math.max(1.0, cellWidth - 1.0), Math.max(1.0, lineHeight - 2.0));
-        } else {
-            gc.strokeRect(x + 0.5, y + 1.0, Math.max(1.0, cellWidth - 1.0), Math.max(1.0, lineHeight - 2.0));
-        }
-    }
-
-    private void drawKittyGraphics(
-            GraphicsContext gc,
-            TerminalPane pane,
-            KittyPlacementLayer layer,
-            Map<KittyPlaceholderKey, KittyPlaceholderBounds> placeholderBounds,
-            double originX,
-            double originY,
-            double cellWidth,
-            double lineHeight
-    ) {
-        pane.kittyGraphics().ifPresent(graphics -> {
-            for (KittyPlacement placement : graphics.placements(layer)) {
-                Image image = imageFor(placement);
-                if (image == null) {
-                    continue;
-                }
-
-                if (placement.virtual()) {
-                    drawVirtualKittyPlacement(gc, placement, image, placeholderBounds, originX, originY, cellWidth, lineHeight);
-                } else {
-                    drawPinnedKittyPlacement(gc, placement, image, originX, originY, cellWidth, lineHeight);
-                }
-            }
-        });
-    }
-
-    private static void drawPinnedKittyPlacement(
-            GraphicsContext gc,
-            KittyPlacement placement,
-            Image image,
-            double originX,
-            double originY,
-            double cellWidth,
-            double lineHeight
-    ) {
-        KittyRenderInfo renderInfo = placement.renderInfo().orElse(null);
-        if (renderInfo == null || !renderInfo.viewportVisible()) {
-            return;
-        }
-
-        double sourceX = renderInfo.sourceX();
-        double sourceY = renderInfo.sourceY();
-        double sourceWidth = renderInfo.sourceWidth();
-        double sourceHeight = renderInfo.sourceHeight();
-        if (sourceWidth <= 0.0 || sourceHeight <= 0.0) {
-            return;
-        }
-
-        double x = originX + (renderInfo.viewportColumn() * cellWidth) + placement.xOffset();
-        double y = originY + (renderInfo.viewportRow() * lineHeight) + placement.yOffset();
-        double width = renderInfo.pixelWidth() > 0 ? renderInfo.pixelWidth() : renderInfo.gridColumns() * cellWidth;
-        double height = renderInfo.pixelHeight() > 0 ? renderInfo.pixelHeight() : renderInfo.gridRows() * lineHeight;
-        if (width <= 0.0 || height <= 0.0) {
-            return;
-        }
-
-        gc.drawImage(image, sourceX, sourceY, sourceWidth, sourceHeight, x, y, width, height);
-    }
-
-    private static void drawVirtualKittyPlacement(
-            GraphicsContext gc,
-            KittyPlacement placement,
-            Image image,
-            Map<KittyPlaceholderKey, KittyPlaceholderBounds> placeholderBounds,
-            double originX,
-            double originY,
-            double cellWidth,
-            double lineHeight
-    ) {
-        KittyPlaceholderBounds bounds = placeholderBounds.get(new KittyPlaceholderKey(placement.imageId(), placement.placementId()));
-        if (bounds == null) {
-            bounds = placeholderBounds.get(new KittyPlaceholderKey(placement.imageId(), 0));
-        }
-        if (bounds == null && placement.placementId() == 0) {
-            bounds = placeholderBounds.entrySet().stream()
-                    .filter(entry -> entry.getKey().imageId() == placement.imageId())
-                    .map(Map.Entry::getValue)
-                    .findFirst()
-                    .orElse(null);
-        }
-        if (bounds == null || bounds.isEmpty()) {
-            return;
-        }
-
-        SourceRect source = sourceRect(placement, image);
-        if (source.width() <= 0.0 || source.height() <= 0.0) {
-            return;
-        }
-
-        long gridColumns = gridColumns(placement, bounds);
-        long gridRows = gridRows(placement, bounds);
-        double sourceCellWidth = source.width() / Math.max(1L, gridColumns);
-        double sourceCellHeight = source.height() / Math.max(1L, gridRows);
-
-        double sourceX = source.x() + (bounds.minSourceColumn * sourceCellWidth);
-        double sourceY = source.y() + (bounds.minSourceRow * sourceCellHeight);
-        double sourceWidth = bounds.sourceColumns() * sourceCellWidth;
-        double sourceHeight = bounds.sourceRows() * sourceCellHeight;
-        double x = originX + (bounds.minColumn * cellWidth);
-        double y = originY + (bounds.minRow * lineHeight);
-        double availableWidth = bounds.columns() * cellWidth;
-        double availableHeight = bounds.rows() * lineHeight;
-
-        if (sourceWidth <= 0.0 || sourceHeight <= 0.0 || availableWidth <= 0.0 || availableHeight <= 0.0) {
-            return;
-        }
-
-        double scale = Math.min(availableWidth / sourceWidth, availableHeight / sourceHeight);
-        double width = sourceWidth * scale;
-        double height = sourceHeight * scale;
-        gc.drawImage(image, sourceX, sourceY, sourceWidth, sourceHeight, x, y, width, height);
-    }
-
-    private static long gridColumns(KittyPlacement placement, KittyPlaceholderBounds bounds) {
-        if (placement.columns() > 0) {
-            return placement.columns();
-        }
-        return Math.max(bounds.maxSourceColumn + 1, bounds.sourceColumns());
-    }
-
-    private static long gridRows(KittyPlacement placement, KittyPlaceholderBounds bounds) {
-        if (placement.rows() > 0) {
-            return placement.rows();
-        }
-        return Math.max(bounds.maxSourceRow + 1, bounds.sourceRows());
-    }
-
-    private static SourceRect sourceRect(KittyPlacement placement, Image image) {
-        double sourceX = placement.sourceX();
-        double sourceY = placement.sourceY();
-        double sourceWidth = placement.sourceWidth() > 0 ? placement.sourceWidth() : image.getWidth() - sourceX;
-        double sourceHeight = placement.sourceHeight() > 0 ? placement.sourceHeight() : image.getHeight() - sourceY;
-        return new SourceRect(sourceX, sourceY, Math.min(sourceWidth, image.getWidth() - sourceX), Math.min(sourceHeight, image.getHeight() - sourceY));
-    }
-
-    private Image imageFor(KittyPlacement placement) {
-        return placement.image().map(snapshot -> {
-            byte[] data = snapshot.data();
-            KittyImageKey key = KittyImageKey.of(snapshot, data);
-            Image cached = kittyImageCache.get(key);
-            if (cached != null) {
-                return cached;
-            }
-
-            kittyImageCache.keySet().removeIf(existing -> existing.id() == snapshot.id());
-            Image decoded = decodeImage(snapshot, data);
-            if (decoded != null) {
-                kittyImageCache.put(key, decoded);
-            }
-            return decoded;
-        }).orElse(null);
-    }
-
-    private boolean paneHasKittyGraphics(TerminalPane pane) {
-        return pane.kittyGraphics()
-                .map(graphics -> !graphics.placements().isEmpty())
-                .orElse(false);
-    }
-
-    private Image decodeImage(KittyImageSnapshot snapshot, byte[] data) {
-        if (snapshot.compression() != KittyImageCompression.NONE) {
-            return null;
-        }
-
-        if (snapshot.format() == KittyImageFormat.PNG) {
-            return new Image(new ByteArrayInputStream(data));
-        }
-
-        int width = Math.toIntExact(snapshot.width());
-        int height = Math.toIntExact(snapshot.height());
-        WritableImage image = new WritableImage(width, height);
-
-        if (snapshot.format() == KittyImageFormat.RGBA) {
-            image.getPixelWriter().setPixels(0, 0, width, height, PixelFormat.getByteBgraInstance(), rgbaToBgra(data), 0, width * 4);
-        } else if (snapshot.format() == KittyImageFormat.RGB) {
-            image.getPixelWriter().setPixels(0, 0, width, height, PixelFormat.getByteRgbInstance(), data, 0, width * 3);
-        }
-        return image;
-    }
-
-    private static byte[] rgbaToBgra(byte[] rgba) {
-        byte[] bgra = new byte[rgba.length];
-        for (int i = 0; i + 3 < rgba.length; i += 4) {
-            bgra[i] = rgba[i + 2];
-            bgra[i + 1] = rgba[i + 1];
-            bgra[i + 2] = rgba[i];
-            bgra[i + 3] = rgba[i + 3];
-        }
-        return bgra;
-    }
-
-    private record FontMetrics(double cellWidth, double lineHeight, double baselineOffset) {
-    }
-
-    private record MouseTarget(MouseEncoderSize size, long screenWidth, long screenHeight) {
-    }
-
-    private record KittyImageKey(long id, long number, long width, long height, KittyImageFormat format, int dataLength, long fingerprint) {
-        private static KittyImageKey of(KittyImageSnapshot snapshot, byte[] data) {
-            return new KittyImageKey(
-                    snapshot.id(),
-                    snapshot.number(),
-                    snapshot.width(),
-                    snapshot.height(),
-                    snapshot.format(),
-                    data.length,
-                    fingerprint(data)
-            );
-        }
-
-        private static long fingerprint(byte[] data) {
-            long hash = 0xcbf29ce484222325L;
-            for (byte value : data) {
-                hash ^= Byte.toUnsignedInt(value);
-                hash *= 0x100000001b3L;
-            }
-            return hash;
-        }
-    }
-
-    private record KittyPlaceholderKey(long imageId, long placementId) {
-    }
-
-    private record SourceRect(double x, double y, double width, double height) {
-    }
-
-    private static final class KittyPlaceholderBounds {
-        private int minRow = Integer.MAX_VALUE;
-        private int maxRow = Integer.MIN_VALUE;
-        private int minColumn = Integer.MAX_VALUE;
-        private int maxColumn = Integer.MIN_VALUE;
-        private long minSourceRow = Long.MAX_VALUE;
-        private long maxSourceRow = Long.MIN_VALUE;
-        private long minSourceColumn = Long.MAX_VALUE;
-        private long maxSourceColumn = Long.MIN_VALUE;
-
-        private void include(int row, int column, KittyPlaceholder placeholder) {
-            minRow = Math.min(minRow, row);
-            maxRow = Math.max(maxRow, row);
-            minColumn = Math.min(minColumn, column);
-            maxColumn = Math.max(maxColumn, column);
-            minSourceRow = Math.min(minSourceRow, placeholder.sourceRow());
-            maxSourceRow = Math.max(maxSourceRow, placeholder.sourceRow());
-            minSourceColumn = Math.min(minSourceColumn, placeholder.sourceColumn());
-            maxSourceColumn = Math.max(maxSourceColumn, placeholder.sourceColumn());
-        }
-
-        private boolean isEmpty() {
-            return minRow == Integer.MAX_VALUE;
-        }
-
-        private int rows() {
-            return maxRow - minRow + 1;
-        }
-
-        private int columns() {
-            return maxColumn - minColumn + 1;
-        }
-
-        private long sourceRows() {
-            return maxSourceRow - minSourceRow + 1;
-        }
-
-        private long sourceColumns() {
-            return maxSourceColumn - minSourceColumn + 1;
-        }
-    }
-
-    private static final class PaneRenderCache {
-        private Canvas canvas;
-        private WritableImage image;
-        private int imageWidth;
-        private int imageHeight;
-        private String key;
-    }
-}

src/main/java/com/gregor/jprototerm/TerminalMetrics.java

@@ -0,0 +1,86 @@
+package com.gregor.jprototerm;
+
+import javafx.scene.text.Font;
+import javafx.scene.text.Text;
+
+/**
+ * Cell geometry shared by the {@link Compositor} and every {@link TerminalPane}.
+ *
+ * <p>The nominal cell width/height come from measuring the font, but a grid can't use
+ * fractional cells, so the measured size is snapped to whole (logical) pixels here — that
+ * snapping is why the value isn't purely a property of the font. The compositor owns the
+ * single instance (it holds the canvas, which is the pixel context), hands it to panes so
+ * they can turn their rect into a column/row count themselves, and re-measures it on a font
+ * change so every pane observes the new geometry through the shared reference.
+ */
+public final class TerminalMetrics {
+    /** Inset, in pixels, between a pane's edge and its content on every side. */
+    public static final double PADDING = 12.0;
+
+    private String fontFamily;
+    private double fontSize;
+    private Font font;
+    private double cellWidth;
+    private double lineHeight;
+    private double baselineOffset;
+
+    public TerminalMetrics(String fontFamily, double fontSize) {
+        setFont(fontFamily, fontSize);
+    }
+
+    public void setFont(String fontFamily, double fontSize) {
+        this.fontFamily = fontFamily;
+        this.fontSize = fontSize;
+        this.font = Font.font(fontFamily, fontSize);
+        measure(font);
+    }
+
+    public String fontFamily() {
+        return fontFamily;
+    }
+
+    public double fontSize() {
+        return fontSize;
+    }
+
+    public Font font() {
+        return font;
+    }
+
+    public double cellWidth() {
+        return cellWidth;
+    }
+
+    public double lineHeight() {
+        return lineHeight;
+    }
+
+    public double baselineOffset() {
+        return baselineOffset;
+    }
+
+    /** Columns that fit in a pane of the given pixel width (after subtracting the padding). */
+    public int columnsFor(double widthPx) {
+        return Math.max(1, (int) ((widthPx - 2 * PADDING) / cellWidth));
+    }
+
+    /** Rows that fit in a pane of the given pixel height (after subtracting the padding). */
+    public int rowsFor(double heightPx) {
+        return Math.max(1, (int) ((heightPx - 2 * PADDING) / lineHeight));
+    }
+
+    private void measure(Font font) {
+        Text text = new Text("┃MgÅjy");
+        text.setFont(font);
+        // Snap the cell size to whole pixels so cells tile on integer boundaries. Fractional
+        // cell metrics put every cell edge on a sub-pixel position, leaving anti-aliased
+        // seams that show up as a faint grid behind the themed cell backgrounds. Rounding
+        // leaves a few pixels of unused space at the right/bottom edge, which is fine.
+        this.lineHeight = Math.max(1.0, Math.round(text.getLayoutBounds().getHeight()));
+        this.baselineOffset = -text.getLayoutBounds().getMinY();
+
+        Text cell = new Text("M");
+        cell.setFont(font);
+        this.cellWidth = Math.max(1.0, Math.round(cell.getLayoutBounds().getWidth()));
+    }
+}

src/main/java/com/gregor/jprototerm/TerminalPane.java

@@ -1,27 +1,39 @@
 package com.gregor.jprototerm;
 
+import dev.jlibghostty.DeviceAttributes;
 import dev.jlibghostty.Ghostty;
 import dev.jlibghostty.KittyGraphics;
 import dev.jlibghostty.MouseAction;
 import dev.jlibghostty.MouseEncoder;
 import dev.jlibghostty.MouseEncoderSize;
 import dev.jlibghostty.MouseInput;
+import dev.jlibghostty.RenderState;
 import dev.jlibghostty.RenderStateSnapshot;
 import dev.jlibghostty.ScrollViewport;
 import dev.jlibghostty.Terminal;
 import dev.jlibghostty.TerminalOptions;
-import dev.jlibghostty.DeviceAttributes;
 
 import java.util.Optional;
-import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.atomic.AtomicLong;
 
+/**
+ * One terminal: owns its ghostty {@link Terminal}, the {@link ShellSession}/pty driving it,
+ * and its on-screen geometry and grid. It does not draw itself; {@link TerminalPaneNode}
+ * reads snapshots from it and represents the visible rows and kitty graphics as JavaFX nodes.
+ */
 public final class TerminalPane implements AutoCloseable {
     private final Terminal terminal;
+    private final TerminalMetrics metrics;
+    private final boolean kittyEnabled;
+    // Run on every content change so the owning tab can bump its content version — the
+    // compositor's O(1) "did the current tab change?" gate.
+    private final Runnable onContentChange;
     private final MouseEncoder mouseEncoder = new MouseEncoder();
-    private final AtomicReference<RenderStateSnapshot> renderSnapshot = new AtomicReference<>();
+    // A persistent render state (reused across frames) is what makes ghostty's per-row dirty
+    // tracking meaningful: update() accumulates dirty since the last resetDirty().
+    private final RenderState renderState = new RenderState();
+    private RenderStateSnapshot cachedSnapshot;
     private ShellSession session;
-    private boolean floating;
-    private boolean visible = true;
     private double x;
     private double y;
     private double width;
@@ -30,22 +42,48 @@ public final class TerminalPane implements AutoCloseable {
     private int rows;
     private int pixelWidth;
     private int pixelHeight;
-    private long renderVersion;
+    private final AtomicLong contentVersion = new AtomicLong();
+    private volatile long snapshotVersion = -1;
 
-    private TerminalPane(Terminal terminal, int columns, int rows) {
+    private TerminalPane(Terminal terminal, TerminalMetrics metrics, boolean kittyEnabled,
+            Runnable onContentChange, int columns, int rows) {
         this.terminal = terminal;
+        this.metrics = metrics;
+        this.kittyEnabled = kittyEnabled;
+        this.onContentChange = onContentChange;
         this.columns = columns;
         this.rows = rows;
     }
 
-    public static TerminalPane create(int columns, int rows, long maxScrollback) {
-        Terminal terminal = Ghostty.open(new TerminalOptions(columns, rows, maxScrollback));
+    /**
+     * Opens a pane sized to fit the given pixel rect: the shared cell metrics decide how many
+     * columns and rows fit, and that grid is handed to ghostty and the shell at start-up. A
+     * non-positive size falls back to the configured default grid (used before the first
+     * layout, when no rect is known yet). The pane owns the shell session it starts and runs
+     * {@code onContentChange} on every content change.
+     */
+    public static TerminalPane create(AppConfig config, TerminalMetrics metrics, Runnable onContentChange, double widthPx, double heightPx) {
+        int columns = widthPx > 0 ? metrics.columnsFor(widthPx) : config.columns();
+        int rows = heightPx > 0 ? metrics.rowsFor(heightPx) : config.rows();
+        Terminal terminal = Ghostty.open(new TerminalOptions(columns, rows, config.maxScrollback()));
         terminal.setDeviceAttributesProvider(DeviceAttributes::xtermCompatible);
-        TerminalPane pane = new TerminalPane(terminal, columns, rows);
+        TerminalPane pane = new TerminalPane(terminal, metrics, config.kittyGraphics(), onContentChange, columns, rows);
         pane.refresh();
+        pane.attach(ShellSession.start(config.shell(), config.envOverride(), pane, columns, rows));
         return pane;
     }
 
+    private void attach(ShellSession session) {
+        this.session = session;
+        terminal.setPtyWriter(bytes -> {
+            ShellSession current = this.session;
+            if (current != null) {
+                current.send(bytes);
+            }
+        });
+        session.startReading(this);
+    }
+
     public void write(String text) {
         synchronized (terminal) {
             terminal.write(text);
@@ -60,17 +98,6 @@ public final class TerminalPane implements AutoCloseable {
         }
     }
 
-    public void attach(ShellSession session) {
-        this.session = session;
-        terminal.setPtyWriter(bytes -> {
-            ShellSession current = this.session;
-            if (current != null) {
-                current.send(bytes);
-            }
-        });
-        session.startReading(this);
-    }
-
     public void send(String text) {
         scrollViewportToBottom();
         if (session != null) {
@@ -104,15 +131,47 @@ public final class TerminalPane implements AutoCloseable {
         }
     }
 
-    public void scrollViewportToBottom() {
+    private void scrollViewportToBottom() {
         synchronized (terminal) {
             terminal.scrollViewport(ScrollViewport.bottom());
             refresh();
         }
     }
 
-    public RenderStateSnapshot renderSnapshot() {
-        return renderSnapshot.get();
+    /**
+     * Incremental snapshot: cells are marshalled only for rows that changed since the last
+     * frame (global dirty == PARTIAL), reused across calls for the same content version.
+     * Snapshotting is deferred here rather than done in refresh(), so a burst of writes
+     * between two frames collapses into a single snapshot.
+     */
+    public RenderStateSnapshot snapshot() {
+        return takeSnapshot(false);
+    }
+
+    /**
+     * Full snapshot with every row's cells populated. Used where the whole pane is redrawn
+     * regardless of dirty state (the kitty-graphics path).
+     */
+    public RenderStateSnapshot snapshotFull() {
+        return takeSnapshot(true);
+    }
+
+    private RenderStateSnapshot takeSnapshot(boolean full) {
+        synchronized (terminal) {
+            long version = contentVersion.get();
+            if (full) {
+                renderState.update(terminal);
+                cachedSnapshot = renderState.snapshot();
+                renderState.resetDirty();
+                snapshotVersion = version;
+            } else if (snapshotVersion != version) {
+                renderState.update(terminal);
+                cachedSnapshot = renderState.snapshotIncremental();
+                renderState.resetDirty();
+                snapshotVersion = version;
+            }
+            return cachedSnapshot;
+        }
     }
 
     public String scrollbackText() {
@@ -121,8 +180,17 @@ public final class TerminalPane implements AutoCloseable {
         }
     }
 
-    public long renderVersion() {
-        return renderVersion;
+    /** This pane's own content revision, bumped on every change (see {@link #refresh()}). */
+    public long contentVersion() {
+        return contentVersion.get();
+    }
+
+    long snapshotVersion() {
+        return snapshotVersion;
+    }
+
+    public boolean kittyEnabled() {
+        return kittyEnabled;
     }
 
     public Optional<KittyGraphics> kittyGraphics() {
@@ -131,22 +199,6 @@ public final class TerminalPane implements AutoCloseable {
         }
     }
 
-    public boolean floating() {
-        return floating;
-    }
-
-    public void setFloating(boolean floating) {
-        this.floating = floating;
-    }
-
-    public boolean visible() {
-        return visible;
-    }
-
-    public void setVisible(boolean visible) {
-        this.visible = visible;
-    }
-
     public double x() {
         return x;
     }
@@ -170,7 +222,14 @@ public final class TerminalPane implements AutoCloseable {
         this.height = height;
     }
 
-    public void resize(int columns, int rows, int pixelWidth, int pixelHeight) {
+    /** Recompute the ghostty grid from the current bounds and the shared cell metrics. */
+    public void fitToBounds() {
+        int columns = metrics.columnsFor(width);
+        int rows = metrics.rowsFor(height);
+        resize(columns, rows, (int) Math.round(metrics.cellWidth()), (int) Math.round(metrics.lineHeight()));
+    }
+
+    private void resize(int columns, int rows, int pixelWidth, int pixelHeight) {
         if (columns <= 0 || rows <= 0 || pixelWidth <= 0 || pixelHeight <= 0) {
             return;
         }
@@ -192,8 +251,11 @@ public final class TerminalPane implements AutoCloseable {
     }
 
     private void refresh() {
-        renderSnapshot.set(terminal.renderSnapshot());
-        renderVersion++;
+        // Mark this pane's content dirty (the snapshot is computed lazily in the paint path,
+        // so a burst of writes collapses into one snapshot per frame) and tell the owning tab
+        // one of its panes changed.
+        contentVersion.incrementAndGet();
+        onContentChange.run();
     }
 
     @Override
@@ -203,6 +265,7 @@ public final class TerminalPane implements AutoCloseable {
             session = null;
         }
         mouseEncoder.close();
+        renderState.close();
         terminal.close();
     }
 }

src/main/java/com/gregor/jprototerm/TerminalPaneNode.java

@@ -0,0 +1,975 @@
+package com.gregor.jprototerm;
+
+import dev.jlibghostty.KittyImageCompression;
+import dev.jlibghostty.KittyImageFormat;
+import dev.jlibghostty.KittyImageSnapshot;
+import dev.jlibghostty.KittyPlacement;
+import dev.jlibghostty.KittyPlacementLayer;
+import dev.jlibghostty.KittyPlaceholder;
+import dev.jlibghostty.KittyRenderInfo;
+import dev.jlibghostty.RenderCell;
+import dev.jlibghostty.RenderColor;
+import dev.jlibghostty.RenderCursorStyle;
+import dev.jlibghostty.RenderRow;
+import dev.jlibghostty.RenderStateSnapshot;
+import javafx.geometry.Rectangle2D;
+import javafx.scene.Node;
+import javafx.scene.canvas.Canvas;
+import javafx.scene.canvas.GraphicsContext;
+import javafx.scene.image.Image;
+import javafx.scene.image.ImageView;
+import javafx.scene.image.PixelFormat;
+import javafx.scene.image.WritableImage;
+import javafx.scene.layout.Pane;
+import javafx.scene.layout.Region;
+import javafx.scene.paint.Color;
+import javafx.scene.shape.Line;
+import javafx.scene.shape.Rectangle;
+import javafx.scene.text.FontSmoothingType;
+
+import java.io.ByteArrayInputStream;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * JavaFX node for one terminal pane. The pane is composed from JavaFX primitives: one node per
+ * terminal row, kitty graphics as ImageView nodes, plus background/cursor/border nodes.
+ */
+final class TerminalPaneNode extends Region {
+    private static final int DIRTY_PARTIAL = 1;
+    private static final int DIRTY_FULL = 2;
+
+    private static final Color DEFAULT_FOREGROUND = Color.rgb(225, 229, 235);
+    private static final Color SELECTED_BACKGROUND = Color.rgb(52, 92, 140);
+    private static final Color PANE_BACKGROUND = Color.rgb(9, 10, 12);
+    private static final Map<Integer, Color> COLOR_CACHE = new HashMap<>();
+
+    private final TerminalPane pane;
+    private final TerminalMetrics metrics;
+    private final Rectangle background = new Rectangle();
+    private final Pane belowImageLayer = new Pane();
+    private final Pane rowLayer = new Pane();
+    private final Pane cursorLayer = new Pane();
+    private final Pane aboveImageLayer = new Pane();
+    private final Rectangle topPadding = new Rectangle();
+    private final Rectangle bottomPadding = new Rectangle();
+    private final Rectangle border = new Rectangle();
+    private final Map<Integer, TerminalRowNode> rows = new HashMap<>();
+    private final Map<Integer, Long> rowFingerprints = new HashMap<>();
+    private final Map<KittyImageKey, Image> kittyImageCache = new HashMap<>();
+    private long drawnContentVersion = Long.MIN_VALUE;
+    private double drawnWidth = -1.0;
+    private double drawnHeight = -1.0;
+
+    TerminalPaneNode(TerminalPane pane, TerminalMetrics metrics) {
+        this.pane = pane;
+        this.metrics = metrics;
+        setPickOnBounds(true);
+        setClip(new Rectangle());
+        background.setFill(PANE_BACKGROUND);
+        border.setFill(Color.TRANSPARENT);
+        getChildren().setAll(background, belowImageLayer, rowLayer, cursorLayer, aboveImageLayer, border);
+        rowLayer.getChildren().setAll(topPadding, bottomPadding);
+    }
+
+    void discard() {
+        drawnContentVersion = Long.MIN_VALUE;
+        drawnWidth = -1.0;
+        drawnHeight = -1.0;
+        rows.clear();
+        rowFingerprints.clear();
+        rowLayer.getChildren().setAll(topPadding, bottomPadding);
+        belowImageLayer.getChildren().clear();
+        aboveImageLayer.getChildren().clear();
+        cursorLayer.getChildren().clear();
+    }
+
+    void renderFull(boolean active) {
+        prepareGeometry();
+        RenderStateSnapshot snapshot = pane.snapshotFull();
+        long renderedVersion = pane.snapshotVersion();
+        boolean withKitty = pane.kittyEnabled() && hasKittyGraphics();
+        updateRowsFull(snapshot);
+        updateKittyGraphics(snapshot, withKitty);
+        updateCursor(snapshot);
+        updateBorder(active);
+        markDrawn(renderedVersion);
+    }
+
+    void renderIncremental(boolean active) {
+        boolean geometryChanged = prepareGeometry();
+        boolean withKitty = pane.kittyEnabled() && hasKittyGraphics();
+        if (drawnContentVersion == Long.MIN_VALUE || geometryChanged || withKitty) {
+            renderFull(active);
+            return;
+        }
+        if (drawnContentVersion == pane.contentVersion()) {
+            updateBorder(active);
+            return;
+        }
+
+        RenderStateSnapshot snapshot = pane.snapshot();
+        long renderedVersion = pane.snapshotVersion();
+        int dirty = snapshot == null ? DIRTY_FULL : snapshot.dirty();
+        if (dirty == DIRTY_FULL) {
+            updateChangedRows(snapshot, snapshot.renderRows());
+        } else if (dirty == DIRTY_PARTIAL) {
+            updateDirtyRows(snapshot);
+        }
+        updateKittyGraphics(snapshot, false);
+        updateCursor(snapshot);
+        updateBorder(active);
+        markDrawn(renderedVersion);
+    }
+
+    private boolean prepareGeometry() {
+        double width = Math.max(0.0, pane.width());
+        double height = Math.max(0.0, pane.height());
+        boolean changed = drawnWidth != width || drawnHeight != height;
+        resize(width, height);
+        background.setWidth(width);
+        background.setHeight(height);
+        resizeLayer(belowImageLayer, width, height);
+        resizeLayer(rowLayer, width, height);
+        resizeLayer(cursorLayer, width, height);
+        resizeLayer(aboveImageLayer, width, height);
+        border.setWidth(Math.max(0.0, width - 1.0));
+        border.setHeight(Math.max(0.0, height - 1.0));
+        border.relocate(0.5, 0.5);
+        Node clip = getClip();
+        if (clip instanceof Rectangle rectangle) {
+            rectangle.setWidth(width);
+            rectangle.setHeight(height);
+        }
+        return changed;
+    }
+
+    private static void resizeLayer(Pane layer, double width, double height) {
+        layer.resizeRelocate(0.0, 0.0, width, height);
+    }
+
+    private void updateRowsFull(RenderStateSnapshot snapshot) {
+        if (snapshot == null) {
+            rows.clear();
+            rowFingerprints.clear();
+            rowLayer.getChildren().setAll(topPadding, bottomPadding);
+            return;
+        }
+
+        List<Node> ordered = new ArrayList<>(snapshot.renderRows().size() + 2);
+        ordered.add(topPadding);
+        ordered.add(bottomPadding);
+        Set<Integer> liveRows = new HashSet<>();
+        for (RenderRow row : snapshot.renderRows()) {
+            TerminalRowNode node = rowNode(row.row());
+            long fingerprint = rowFingerprint(row);
+            node.render(row);
+            rowFingerprints.put(row.row(), fingerprint);
+            liveRows.add(row.row());
+            ordered.add(node);
+        }
+        rows.keySet().retainAll(liveRows);
+        rowFingerprints.keySet().retainAll(liveRows);
+        rowLayer.getChildren().setAll(ordered);
+        updateVerticalPadding(snapshot);
+    }
+
+    private void updateDirtyRows(RenderStateSnapshot snapshot) {
+        List<RenderRow> dirtyRows = snapshot.renderRows().stream()
+                .filter(RenderRow::dirty)
+                .toList();
+        updateChangedRows(snapshot, dirtyRows);
+    }
+
+    private void updateChangedRows(RenderStateSnapshot snapshot, List<RenderRow> changedRows) {
+        if (snapshot == null || changedRows.isEmpty()) {
+            return;
+        }
+
+        Set<Integer> movedRows = moveShiftedRows(snapshot, changedRows);
+        for (RenderRow row : snapshot.renderRows()) {
+            if (!changedRows.contains(row) || movedRows.contains(row.row())) {
+                continue;
+            }
+            TerminalRowNode node = rowNode(row.row());
+            long fingerprint = rowFingerprint(row);
+            node.renderChanged(row);
+            rowFingerprints.put(row.row(), fingerprint);
+        }
+        for (RenderRow row : changedRows) {
+            updateDirtyVerticalPadding(snapshot, row);
+        }
+        syncRowChildren();
+    }
+
+    private Set<Integer> moveShiftedRows(RenderStateSnapshot snapshot, List<RenderRow> changedRows) {
+        if (rowFingerprints.isEmpty() || changedRows.size() < Math.max(4, snapshot.rows() / 3)) {
+            return Set.of();
+        }
+
+        ShiftPlan plan = detectShift(snapshot, changedRows);
+        if (plan == null) {
+            return Set.of();
+        }
+
+        Map<Integer, TerminalRowNode> oldRows = new HashMap<>(rows);
+        Map<Integer, Long> oldFingerprints = new HashMap<>(rowFingerprints);
+        for (RowMove move : plan.moves()) {
+            rows.remove(move.sourceRow());
+            rowFingerprints.remove(move.sourceRow());
+        }
+        for (RowMove move : plan.moves()) {
+            TerminalRowNode node = oldRows.get(move.sourceRow());
+            if (node == null) {
+                continue;
+            }
+            node.moveToRow(move.targetRow());
+            rows.put(move.targetRow(), node);
+            rowFingerprints.put(move.targetRow(), oldFingerprints.get(move.sourceRow()));
+        }
+        return plan.targetRows();
+    }
+
+    private ShiftPlan detectShift(RenderStateSnapshot snapshot, List<RenderRow> changedRows) {
+        int bestDelta = 0;
+        int bestScore = 0;
+        int rowCount = snapshot.rows();
+        for (int delta = -rowCount + 1; delta < rowCount; delta++) {
+            if (delta == 0) {
+                continue;
+            }
+            int score = 0;
+            for (RenderRow row : changedRows) {
+                int sourceRow = row.row() + delta;
+                if (sourceRow < 0 || sourceRow >= rowCount || !rows.containsKey(sourceRow)) {
+                    continue;
+                }
+                Long previous = rowFingerprints.get(sourceRow);
+                if (previous != null && previous == rowFingerprint(row)) {
+                    score++;
+                }
+            }
+            if (score > bestScore) {
+                bestScore = score;
+                bestDelta = delta;
+            }
+        }
+
+        int threshold = Math.max(4, (changedRows.size() * 2 + 2) / 3);
+        if (bestScore < threshold) {
+            return null;
+        }
+
+        List<RowMove> moves = new ArrayList<>(bestScore);
+        Set<Integer> targetRows = new HashSet<>();
+        for (RenderRow row : changedRows) {
+            int sourceRow = row.row() + bestDelta;
+            if (sourceRow < 0 || sourceRow >= rowCount || !rows.containsKey(sourceRow)) {
+                continue;
+            }
+            Long previous = rowFingerprints.get(sourceRow);
+            if (previous != null && previous == rowFingerprint(row)) {
+                moves.add(new RowMove(sourceRow, row.row()));
+                targetRows.add(row.row());
+            }
+        }
+        return new ShiftPlan(moves, targetRows);
+    }
+
+    private void syncRowChildren() {
+        List<Node> ordered = new ArrayList<>(rows.size() + 2);
+        ordered.add(topPadding);
+        ordered.add(bottomPadding);
+        rows.entrySet().stream()
+                .sorted(Comparator.comparingInt(Map.Entry::getKey))
+                .map(Map.Entry::getValue)
+                .forEach(ordered::add);
+        rowLayer.getChildren().setAll(ordered);
+    }
+
+    private TerminalRowNode rowNode(int row) {
+        return rows.computeIfAbsent(row, ignored -> {
+            TerminalRowNode created = new TerminalRowNode(metrics);
+            if (!rowLayer.getChildren().contains(created)) {
+                rowLayer.getChildren().add(created);
+            }
+            return created;
+        });
+    }
+
+    private void updateVerticalPadding(RenderStateSnapshot snapshot) {
+        List<RenderRow> renderRows = snapshot.renderRows();
+        if (renderRows.isEmpty()) {
+            topPadding.setVisible(false);
+            bottomPadding.setVisible(false);
+            return;
+        }
+
+        double width = pane.width();
+        double top = TerminalMetrics.PADDING;
+        double contentBottom = top + snapshot.rows() * metrics.lineHeight();
+        topPadding.setVisible(true);
+        topPadding.setFill(rowEdgeBackground(renderRows.get(0), true));
+        topPadding.relocate(0.0, 0.0);
+        topPadding.setWidth(width);
+        topPadding.setHeight(top);
+
+        bottomPadding.setVisible(true);
+        bottomPadding.setFill(rowEdgeBackground(renderRows.get(renderRows.size() - 1), true));
+        bottomPadding.relocate(0.0, contentBottom);
+        bottomPadding.setWidth(width);
+        bottomPadding.setHeight(Math.max(0.0, pane.height() - contentBottom));
+    }
+
+    private void updateDirtyVerticalPadding(RenderStateSnapshot snapshot, RenderRow row) {
+        if (row.row() == 0) {
+            topPadding.setVisible(true);
+            topPadding.setFill(rowEdgeBackground(row, true));
+            topPadding.relocate(0.0, 0.0);
+            topPadding.setWidth(pane.width());
+            topPadding.setHeight(TerminalMetrics.PADDING);
+        }
+        if (row.row() == snapshot.rows() - 1) {
+            double contentBottom = TerminalMetrics.PADDING + snapshot.rows() * metrics.lineHeight();
+            bottomPadding.setVisible(true);
+            bottomPadding.setFill(rowEdgeBackground(row, true));
+            bottomPadding.relocate(0.0, contentBottom);
+            bottomPadding.setWidth(pane.width());
+            bottomPadding.setHeight(Math.max(0.0, pane.height() - contentBottom));
+        }
+    }
+
+    private void updateCursor(RenderStateSnapshot snapshot) {
+        cursorLayer.getChildren().clear();
+        if (snapshot == null || !snapshot.cursorVisible() || !snapshot.cursorViewportHasValue()) {
+            return;
+        }
+
+        double x = TerminalMetrics.PADDING + (snapshot.cursorViewportX() * metrics.cellWidth());
+        double y = TerminalMetrics.PADDING + (snapshot.cursorViewportY() * metrics.lineHeight());
+        double cellWidth = metrics.cellWidth();
+        double lineHeight = metrics.lineHeight();
+        RenderCursorStyle style = snapshot.cursorStyle();
+        if (style == RenderCursorStyle.BAR) {
+            Line line = new Line(x + 0.5, y + 2.0, x + 0.5, y + lineHeight - 2.0);
+            line.setStroke(DEFAULT_FOREGROUND);
+            line.setStrokeWidth(1.5);
+            cursorLayer.getChildren().add(line);
+        } else if (style == RenderCursorStyle.UNDERLINE) {
+            Line line = new Line(x + 1.0, y + lineHeight - 2.0, x + cellWidth - 1.0, y + lineHeight - 2.0);
+            line.setStroke(DEFAULT_FOREGROUND);
+            line.setStrokeWidth(1.5);
+            cursorLayer.getChildren().add(line);
+        } else if (style == RenderCursorStyle.BLOCK) {
+            Rectangle rectangle = new Rectangle(x + 0.5, y + 1.0, Math.max(1.0, cellWidth - 1.0), Math.max(1.0, lineHeight - 2.0));
+            rectangle.setFill(Color.rgb(225, 229, 235, 0.28));
+            cursorLayer.getChildren().add(rectangle);
+        } else {
+            Rectangle rectangle = new Rectangle(x + 0.5, y + 1.0, Math.max(1.0, cellWidth - 1.0), Math.max(1.0, lineHeight - 2.0));
+            rectangle.setFill(Color.TRANSPARENT);
+            rectangle.setStroke(DEFAULT_FOREGROUND);
+            rectangle.setStrokeWidth(1.5);
+            cursorLayer.getChildren().add(rectangle);
+        }
+    }
+
+    private void updateBorder(boolean active) {
+        border.setStroke(active ? Color.rgb(87, 166, 255) : Color.rgb(52, 57, 65));
+        border.setStrokeWidth(active ? 2.0 : 1.0);
+    }
+
+    private void updateKittyGraphics(RenderStateSnapshot snapshot, boolean withKitty) {
+        belowImageLayer.getChildren().clear();
+        aboveImageLayer.getChildren().clear();
+        if (!withKitty || snapshot == null) {
+            return;
+        }
+
+        Map<KittyPlaceholderKey, KittyPlaceholderBounds> placeholderBounds = kittyPlaceholderBounds(snapshot);
+        addKittyGraphics(belowImageLayer, KittyPlacementLayer.BELOW_TEXT, placeholderBounds);
+        addKittyGraphics(aboveImageLayer, KittyPlacementLayer.ABOVE_TEXT, placeholderBounds);
+    }
+
+    private void addKittyGraphics(Pane layer, KittyPlacementLayer placementLayer, Map<KittyPlaceholderKey, KittyPlaceholderBounds> placeholderBounds) {
+        pane.kittyGraphics().ifPresent(graphics -> {
+            for (KittyPlacement placement : graphics.placements(placementLayer)) {
+                Image image = imageFor(placement);
+                if (image == null) {
+                    continue;
+                }
+                ImageView view = placement.virtual()
+                        ? virtualKittyView(placement, image, placeholderBounds)
+                        : pinnedKittyView(placement, image);
+                if (view != null) {
+                    layer.getChildren().add(view);
+                }
+            }
+        });
+    }
+
+    private ImageView pinnedKittyView(KittyPlacement placement, Image image) {
+        KittyRenderInfo renderInfo = placement.renderInfo().orElse(null);
+        if (renderInfo == null || !renderInfo.viewportVisible()) {
+            return null;
+        }
+
+        double sourceX = renderInfo.sourceX();
+        double sourceY = renderInfo.sourceY();
+        double sourceWidth = renderInfo.sourceWidth();
+        double sourceHeight = renderInfo.sourceHeight();
+        if (sourceWidth <= 0.0 || sourceHeight <= 0.0) {
+            return null;
+        }
+
+        double x = TerminalMetrics.PADDING + (renderInfo.viewportColumn() * metrics.cellWidth()) + placement.xOffset();
+        double y = TerminalMetrics.PADDING + (renderInfo.viewportRow() * metrics.lineHeight()) + placement.yOffset();
+        double width = renderInfo.pixelWidth() > 0 ? renderInfo.pixelWidth() : renderInfo.gridColumns() * metrics.cellWidth();
+        double height = renderInfo.pixelHeight() > 0 ? renderInfo.pixelHeight() : renderInfo.gridRows() * metrics.lineHeight();
+        return imageView(image, sourceX, sourceY, sourceWidth, sourceHeight, x, y, width, height);
+    }
+
+    private ImageView virtualKittyView(KittyPlacement placement, Image image, Map<KittyPlaceholderKey, KittyPlaceholderBounds> placeholderBounds) {
+        KittyPlaceholderBounds bounds = placeholderBounds.get(new KittyPlaceholderKey(placement.imageId(), placement.placementId()));
+        if (bounds == null) {
+            bounds = placeholderBounds.get(new KittyPlaceholderKey(placement.imageId(), 0));
+        }
+        if (bounds == null && placement.placementId() == 0) {
+            bounds = placeholderBounds.entrySet().stream()
+                    .filter(entry -> entry.getKey().imageId() == placement.imageId())
+                    .map(Map.Entry::getValue)
+                    .findFirst()
+                    .orElse(null);
+        }
+        if (bounds == null || bounds.isEmpty()) {
+            return null;
+        }
+
+        SourceRect source = sourceRect(placement, image);
+        if (source.width() <= 0.0 || source.height() <= 0.0) {
+            return null;
+        }
+
+        long gridColumns = gridColumns(placement, bounds);
+        long gridRows = gridRows(placement, bounds);
+        double sourceCellWidth = source.width() / Math.max(1L, gridColumns);
+        double sourceCellHeight = source.height() / Math.max(1L, gridRows);
+
+        double sourceX = source.x() + (bounds.minSourceColumn * sourceCellWidth);
+        double sourceY = source.y() + (bounds.minSourceRow * sourceCellHeight);
+        double sourceWidth = bounds.sourceColumns() * sourceCellWidth;
+        double sourceHeight = bounds.sourceRows() * sourceCellHeight;
+        double x = TerminalMetrics.PADDING + (bounds.minColumn * metrics.cellWidth());
+        double y = TerminalMetrics.PADDING + (bounds.minRow * metrics.lineHeight());
+        double availableWidth = bounds.columns() * metrics.cellWidth();
+        double availableHeight = bounds.rows() * metrics.lineHeight();
+        if (sourceWidth <= 0.0 || sourceHeight <= 0.0 || availableWidth <= 0.0 || availableHeight <= 0.0) {
+            return null;
+        }
+
+        double scale = Math.min(availableWidth / sourceWidth, availableHeight / sourceHeight);
+        return imageView(image, sourceX, sourceY, sourceWidth, sourceHeight, x, y, sourceWidth * scale, sourceHeight * scale);
+    }
+
+    private static ImageView imageView(Image image, double sourceX, double sourceY, double sourceWidth, double sourceHeight,
+            double x, double y, double width, double height) {
+        if (width <= 0.0 || height <= 0.0) {
+            return null;
+        }
+        ImageView view = new ImageView(image);
+        view.setViewport(new Rectangle2D(sourceX, sourceY, sourceWidth, sourceHeight));
+        view.setFitWidth(width);
+        view.setFitHeight(height);
+        view.setPreserveRatio(false);
+        view.relocate(x, y);
+        return view;
+    }
+
+    private boolean hasKittyGraphics() {
+        return pane.kittyGraphics()
+                .map(graphics -> !graphics.placements().isEmpty())
+                .orElse(false);
+    }
+
+    private Image imageFor(KittyPlacement placement) {
+        return placement.image().map(snapshot -> {
+            byte[] data = snapshot.data();
+            KittyImageKey key = KittyImageKey.of(snapshot, data);
+            Image cached = kittyImageCache.get(key);
+            if (cached != null) {
+                return cached;
+            }
+
+            kittyImageCache.keySet().removeIf(existing -> existing.id() == snapshot.id());
+            Image decoded = decodeImage(snapshot, data);
+            if (decoded != null) {
+                kittyImageCache.put(key, decoded);
+            }
+            return decoded;
+        }).orElse(null);
+    }
+
+    private static Image decodeImage(KittyImageSnapshot snapshot, byte[] data) {
+        if (snapshot.compression() != KittyImageCompression.NONE) {
+            return null;
+        }
+
+        if (snapshot.format() == KittyImageFormat.PNG) {
+            return new Image(new ByteArrayInputStream(data));
+        }
+
+        int width = Math.toIntExact(snapshot.width());
+        int height = Math.toIntExact(snapshot.height());
+        WritableImage image = new WritableImage(width, height);
+
+        if (snapshot.format() == KittyImageFormat.RGBA) {
+            image.getPixelWriter().setPixels(0, 0, width, height, PixelFormat.getByteBgraInstance(), rgbaToBgra(data), 0, width * 4);
+        } else if (snapshot.format() == KittyImageFormat.RGB) {
+            image.getPixelWriter().setPixels(0, 0, width, height, PixelFormat.getByteRgbInstance(), data, 0, width * 3);
+        }
+        return image;
+    }
+
+    private static byte[] rgbaToBgra(byte[] rgba) {
+        byte[] bgra = new byte[rgba.length];
+        for (int i = 0; i + 3 < rgba.length; i += 4) {
+            bgra[i] = rgba[i + 2];
+            bgra[i + 1] = rgba[i + 1];
+            bgra[i + 2] = rgba[i];
+            bgra[i + 3] = rgba[i + 3];
+        }
+        return bgra;
+    }
+
+    private static Map<KittyPlaceholderKey, KittyPlaceholderBounds> kittyPlaceholderBounds(RenderStateSnapshot snapshot) {
+        Map<KittyPlaceholderKey, KittyPlaceholderBounds> result = new HashMap<>();
+        for (RenderRow row : snapshot.renderRows()) {
+            for (RenderCell cell : row.cells()) {
+                cell.kittyPlaceholder().ifPresent(placeholder -> {
+                    KittyPlaceholderKey key = new KittyPlaceholderKey(placeholder.imageId(), placeholder.placementId());
+                    result.computeIfAbsent(key, ignored -> new KittyPlaceholderBounds()).include(row.row(), cell.column(), placeholder);
+                });
+            }
+        }
+        return result;
+    }
+
+    private static long gridColumns(KittyPlacement placement, KittyPlaceholderBounds bounds) {
+        if (placement.columns() > 0) {
+            return placement.columns();
+        }
+        return Math.max(bounds.maxSourceColumn + 1, bounds.sourceColumns());
+    }
+
+    private static long gridRows(KittyPlacement placement, KittyPlaceholderBounds bounds) {
+        if (placement.rows() > 0) {
+            return placement.rows();
+        }
+        return Math.max(bounds.maxSourceRow + 1, bounds.sourceRows());
+    }
+
+    private static SourceRect sourceRect(KittyPlacement placement, Image image) {
+        double sourceX = placement.sourceX();
+        double sourceY = placement.sourceY();
+        double sourceWidth = placement.sourceWidth() > 0 ? placement.sourceWidth() : image.getWidth() - sourceX;
+        double sourceHeight = placement.sourceHeight() > 0 ? placement.sourceHeight() : image.getHeight() - sourceY;
+        return new SourceRect(sourceX, sourceY, Math.min(sourceWidth, image.getWidth() - sourceX), Math.min(sourceHeight, image.getHeight() - sourceY));
+    }
+
+    private void markDrawn(long renderedVersion) {
+        drawnContentVersion = renderedVersion;
+        drawnWidth = pane.width();
+        drawnHeight = pane.height();
+    }
+
+    private static Color cellBackgroundColor(RenderCell cell) {
+        if (cell.inverse()) {
+            var fg = cell.foreground();
+            return fg.isPresent() ? toFxColor(fg.get()) : DEFAULT_FOREGROUND;
+        }
+        var bg = cell.background();
+        return bg.isPresent() ? toFxColor(bg.get()) : PANE_BACKGROUND;
+    }
+
+    private static Color rowEdgeBackground(RenderRow row, boolean firstCell) {
+        List<RenderCell> cells = row.cells();
+        if (cells.isEmpty()) {
+            return PANE_BACKGROUND;
+        }
+        return cellBackgroundColor(firstCell ? cells.get(0) : cells.get(cells.size() - 1));
+    }
+
+    private static Color cellBackgroundOverride(RenderCell cell) {
+        if (cell.inverse()) {
+            var fg = cell.foreground();
+            return fg.isPresent() ? toFxColor(fg.get()) : DEFAULT_FOREGROUND;
+        }
+        var bg = cell.background();
+        return bg.isPresent() ? toFxColor(bg.get()) : null;
+    }
+
+    private static Color cellForegroundColor(RenderCell cell) {
+        var fgOpt = cell.foreground();
+        var bgOpt = cell.background();
+        Color fg = fgOpt.isPresent() ? toFxColor(fgOpt.get()) : DEFAULT_FOREGROUND;
+        Color bg = bgOpt.isPresent() ? toFxColor(bgOpt.get()) : null;
+
+        if (cell.inverse()) {
+            return (bg != null) ? bg : PANE_BACKGROUND;
+        }
+        return fg;
+    }
+
+    private static Color toFxColor(RenderColor color) {
+        int key = (color.red() << 16) | (color.green() << 8) | color.blue();
+        Color cached = COLOR_CACHE.get(key);
+        if (cached != null) {
+            return cached;
+        }
+        if (COLOR_CACHE.size() >= 4096) {
+            COLOR_CACHE.clear();
+        }
+        Color created = Color.rgb(color.red(), color.green(), color.blue());
+        COLOR_CACHE.put(key, created);
+        return created;
+    }
+
+    private static long rowFingerprint(RenderRow row) {
+        long hash = 0xcbf29ce484222325L;
+        hash = mix(hash, row.cells().size());
+        for (RenderCell cell : row.cells()) {
+            hash = mix(hash, cellFingerprint(cell));
+        }
+        return hash;
+    }
+
+    private static long cellFingerprint(RenderCell cell) {
+        long hash = 0xcbf29ce484222325L;
+        hash = mix(hash, cell.column());
+        hash = mix(hash, cell.inverse() ? 1 : 0);
+        hash = mix(hash, cell.selected() ? 1 : 0);
+        hash = mix(hash, colorFingerprint(cell.foreground().orElse(null)));
+        hash = mix(hash, colorFingerprint(cell.background().orElse(null)));
+        for (int codepoint : cell.codepoints()) {
+            hash = mix(hash, codepoint);
+        }
+        if (cell.kittyPlaceholder().isPresent()) {
+            KittyPlaceholder placeholder = cell.kittyPlaceholder().get();
+            hash = mix(hash, placeholder.imageId());
+            hash = mix(hash, placeholder.placementId());
+            hash = mix(hash, placeholder.sourceRow());
+            hash = mix(hash, placeholder.sourceColumn());
+        }
+        return hash;
+    }
+
+    private static long colorFingerprint(RenderColor color) {
+        if (color == null) {
+            return -1L;
+        }
+        return ((long) color.red() << 16) | ((long) color.green() << 8) | color.blue();
+    }
+
+    private static long mix(long hash, long value) {
+        hash ^= value;
+        return hash * 0x100000001b3L;
+    }
+
+    private static final class TerminalRowNode extends Region {
+        private final TerminalMetrics metrics;
+        private final Canvas canvas = new Canvas();
+        private long[] cellFingerprints = new long[0];
+
+        private TerminalRowNode(TerminalMetrics metrics) {
+            this.metrics = metrics;
+            getChildren().add(canvas);
+        }
+
+        private void render(RenderRow row) {
+            prepareCanvas(row);
+
+            GraphicsContext gc = canvas.getGraphicsContext2D();
+            gc.clearRect(0.0, 0.0, canvas.getWidth(), canvas.getHeight());
+            gc.setFontSmoothingType(FontSmoothingType.LCD);
+            gc.setFont(metrics.font());
+
+            paintSidePadding(gc, row, canvas.getWidth(), canvas.getHeight());
+            drawRow(gc, row, rowTop(row), metrics.cellWidth(), metrics.lineHeight());
+            cellFingerprints = cellFingerprints(row);
+        }
+
+        private void renderChanged(RenderRow row) {
+            double oldWidth = canvas.getWidth();
+            double oldHeight = canvas.getHeight();
+            prepareCanvas(row);
+            long[] nextFingerprints = cellFingerprints(row);
+            if (cellFingerprints.length != nextFingerprints.length
+                    || oldWidth != canvas.getWidth()
+                    || oldHeight != canvas.getHeight()) {
+                render(row);
+                return;
+            }
+
+            GraphicsContext gc = canvas.getGraphicsContext2D();
+            gc.setFontSmoothingType(FontSmoothingType.LCD);
+            gc.setFont(metrics.font());
+
+            int runStart = -1;
+            int runEnd = -1;
+            for (int column = 0; column < nextFingerprints.length; column++) {
+                if (cellFingerprints[column] == nextFingerprints[column]) {
+                    continue;
+                }
+
+                int start = Math.max(0, column - 1);
+                int end = Math.min(nextFingerprints.length - 1, column + 1);
+                if (runStart < 0) {
+                    runStart = start;
+                    runEnd = end;
+                } else if (start <= runEnd + 1) {
+                    runEnd = Math.max(runEnd, end);
+                } else {
+                    repaintColumns(gc, row, runStart, runEnd);
+                    runStart = start;
+                    runEnd = end;
+                }
+            }
+            if (runStart >= 0) {
+                repaintColumns(gc, row, runStart, runEnd);
+            }
+            cellFingerprints = nextFingerprints;
+        }
+
+        private void prepareCanvas(RenderRow row) {
+            double paneWidth = ((Region) getParent()).getWidth();
+            double rowTop = rowTop(row);
+            double rowBottom = rowBottom(row);
+            double rowHeight = Math.max(1.0, rowBottom - rowTop);
+            resizeRelocate(0.0, rowTop, paneWidth, rowHeight);
+            canvas.setWidth(Math.max(0.0, paneWidth));
+            canvas.setHeight(rowHeight);
+        }
+
+        private void moveToRow(int row) {
+            double paneWidth = ((Region) getParent()).getWidth();
+            double rowTop = rowTop(row);
+            double rowBottom = rowBottom(row);
+            double rowHeight = Math.max(1.0, rowBottom - rowTop);
+            resizeRelocate(0.0, rowTop, paneWidth, rowHeight);
+            canvas.setWidth(Math.max(0.0, paneWidth));
+            canvas.setHeight(rowHeight);
+        }
+
+        private double rowTop(RenderRow row) {
+            return rowTop(row.row());
+        }
+
+        private double rowTop(int row) {
+            return Math.floor(TerminalMetrics.PADDING + row * metrics.lineHeight());
+        }
+
+        private double rowBottom(RenderRow row) {
+            return rowBottom(row.row());
+        }
+
+        private double rowBottom(int row) {
+            return Math.ceil(TerminalMetrics.PADDING + (row + 1) * metrics.lineHeight());
+        }
+
+        private void repaintColumns(GraphicsContext gc, RenderRow row, int startColumn, int endColumn) {
+            if (endColumn < startColumn) {
+                return;
+            }
+
+            double cellWidth = metrics.cellWidth();
+            double lineHeight = metrics.lineHeight();
+            double rowTop = rowTop(row);
+            double contentTop = TerminalMetrics.PADDING + row.row() * lineHeight;
+            double localCellTop = contentTop - rowTop;
+            double baseline = TerminalMetrics.PADDING + metrics.baselineOffset() + row.row() * lineHeight - rowTop;
+            double x = TerminalMetrics.PADDING + startColumn * cellWidth;
+            double width = (endColumn - startColumn + 1) * cellWidth;
+
+            gc.clearRect(x, 0.0, width, canvas.getHeight());
+            if (startColumn == 0) {
+                gc.setFill(rowEdgeBackground(row, true));
+                gc.fillRect(0.0, 0.0, TerminalMetrics.PADDING, canvas.getHeight());
+            }
+            if (endColumn >= row.cells().size() - 1) {
+                double contentRight = TerminalMetrics.PADDING + row.cells().size() * cellWidth;
+                gc.setFill(rowEdgeBackground(row, false));
+                gc.fillRect(contentRight, 0.0, canvas.getWidth() - contentRight, canvas.getHeight());
+            }
+
+            drawRowBackgrounds(gc, row, localCellTop, cellWidth, lineHeight, startColumn, endColumn);
+            drawRowText(gc, row, baseline, cellWidth, startColumn, endColumn);
+        }
+
+        private void paintSidePadding(GraphicsContext gc, RenderRow row, double paneWidth, double bandHeight) {
+            int columns = row.cells().size();
+            if (columns == 0) {
+                return;
+            }
+            double contentLeft = TerminalMetrics.PADDING;
+            double contentRight = contentLeft + columns * metrics.cellWidth();
+            gc.setFill(rowEdgeBackground(row, true));
+            gc.fillRect(0.0, 0.0, contentLeft, bandHeight);
+            gc.setFill(rowEdgeBackground(row, false));
+            gc.fillRect(contentRight, 0.0, paneWidth - contentRight, bandHeight);
+        }
+
+        private void drawRow(GraphicsContext gc, RenderRow row, double rowTop, double cellWidth, double lineHeight) {
+            double contentTop = TerminalMetrics.PADDING + row.row() * lineHeight;
+            double localCellTop = contentTop - rowTop;
+            double baseline = TerminalMetrics.PADDING + metrics.baselineOffset() + row.row() * lineHeight - rowTop;
+            drawRowBackgrounds(gc, row, localCellTop, cellWidth, lineHeight, 0, row.cells().size() - 1);
+            drawRowText(gc, row, baseline, cellWidth, 0, row.cells().size() - 1);
+        }
+
+        private void drawRowBackgrounds(GraphicsContext gc, RenderRow row, double localCellTop,
+                double cellWidth, double lineHeight, int startColumn, int endColumn) {
+            Color runBackground = null;
+            int runStartColumn = 0;
+            int previousColumn = -1;
+            for (RenderCell cell : row.cells()) {
+                if (cell.column() < startColumn || cell.column() > endColumn) {
+                    continue;
+                }
+                if (cell.kittyPlaceholder().isPresent()) {
+                    flushBackgroundRun(gc, runBackground, localCellTop, cellWidth, lineHeight, runStartColumn, previousColumn);
+                    runBackground = null;
+                    previousColumn = -1;
+                    continue;
+                }
+
+                Color background = cell.selected() ? SELECTED_BACKGROUND : cellBackgroundOverride(cell);
+                if (background == null) {
+                    flushBackgroundRun(gc, runBackground, localCellTop, cellWidth, lineHeight, runStartColumn, previousColumn);
+                    runBackground = null;
+                    previousColumn = -1;
+                    continue;
+                }
+
+                if (runBackground == null || background != runBackground || cell.column() != previousColumn + 1) {
+                    flushBackgroundRun(gc, runBackground, localCellTop, cellWidth, lineHeight, runStartColumn, previousColumn);
+                    runBackground = background;
+                    runStartColumn = cell.column();
+                }
+                previousColumn = cell.column();
+            }
+            flushBackgroundRun(gc, runBackground, localCellTop, cellWidth, lineHeight, runStartColumn, previousColumn);
+        }
+
+        private void flushBackgroundRun(GraphicsContext gc, Color background, double localCellTop,
+                double cellWidth, double lineHeight, int startColumn, int endColumn) {
+            if (background == null || endColumn < startColumn) {
+                return;
+            }
+            gc.setFill(background);
+            gc.fillRect(
+                    TerminalMetrics.PADDING + startColumn * cellWidth,
+                    localCellTop,
+                    (endColumn - startColumn + 1) * cellWidth,
+                    lineHeight);
+        }
+
+        private void drawRowText(GraphicsContext gc, RenderRow row, double baseline,
+                double cellWidth, int startColumn, int endColumn) {
+            for (RenderCell cell : row.cells()) {
+                if (cell.column() < startColumn || cell.column() > endColumn) {
+                    continue;
+                }
+                if (cell.kittyPlaceholder().isPresent() || cell.codepoints().length == 0) {
+                    continue;
+                }
+
+                gc.setFill(cellForegroundColor(cell));
+                gc.fillText(cell.text(), TerminalMetrics.PADDING + cell.column() * cellWidth, baseline);
+            }
+        }
+
+        private static long[] cellFingerprints(RenderRow row) {
+            int columns = row.cells().size();
+            for (RenderCell cell : row.cells()) {
+                columns = Math.max(columns, cell.column() + 1);
+            }
+
+            long[] fingerprints = new long[columns];
+            for (RenderCell cell : row.cells()) {
+                fingerprints[cell.column()] = cellFingerprint(cell);
+            }
+            return fingerprints;
+        }
+    }
+
+    private record KittyImageKey(long id, long number, long width, long height, KittyImageFormat format, int dataLength) {
+        private static KittyImageKey of(KittyImageSnapshot snapshot, byte[] data) {
+            return new KittyImageKey(
+                    snapshot.id(),
+                    snapshot.number(),
+                    snapshot.width(),
+                    snapshot.height(),
+                    snapshot.format(),
+                    data.length
+            );
+        }
+    }
+
+    private record KittyPlaceholderKey(long imageId, long placementId) {
+    }
+
+    private record SourceRect(double x, double y, double width, double height) {
+    }
+
+    private record RowMove(int sourceRow, int targetRow) {
+    }
+
+    private record ShiftPlan(List<RowMove> moves, Set<Integer> targetRows) {
+    }
+
+    private static final class KittyPlaceholderBounds {
+        private int minRow = Integer.MAX_VALUE;
+        private int maxRow = Integer.MIN_VALUE;
+        private int minColumn = Integer.MAX_VALUE;
+        private int maxColumn = Integer.MIN_VALUE;
+        private long minSourceRow = Long.MAX_VALUE;
+        private long maxSourceRow = Long.MIN_VALUE;
+        private long minSourceColumn = Long.MAX_VALUE;
+        private long maxSourceColumn = Long.MIN_VALUE;
+
+        private void include(int row, int column, KittyPlaceholder placeholder) {
+            minRow = Math.min(minRow, row);
+            maxRow = Math.max(maxRow, row);
+            minColumn = Math.min(minColumn, column);
+            maxColumn = Math.max(maxColumn, column);
+            minSourceRow = Math.min(minSourceRow, placeholder.sourceRow());
+            maxSourceRow = Math.max(maxSourceRow, placeholder.sourceRow());
+            minSourceColumn = Math.min(minSourceColumn, placeholder.sourceColumn());
+            maxSourceColumn = Math.max(maxSourceColumn, placeholder.sourceColumn());
+        }
+
+        private boolean isEmpty() {
+            return minRow == Integer.MAX_VALUE;
+        }
+
+        private int rows() {
+            return maxRow - minRow + 1;
+        }
+
+        private int columns() {
+            return maxColumn - minColumn + 1;
+        }
+
+        private long sourceRows() {
+            return maxSourceRow - minSourceRow + 1;
+        }
+
+        private long sourceColumns() {
+            return maxSourceColumn - minSourceColumn + 1;
+        }
+    }
+}

src/main/java/com/gregor/jprototerm/TerminalWorkspace.java

@@ -1,293 +0,0 @@
-package com.gregor.jprototerm;
-
-import java.util.ArrayList;
-import java.util.Comparator;
-import java.util.List;
-
-public final class TerminalWorkspace implements AutoCloseable {
-    private final AppConfig config;
-    private final List<TerminalPane> panes = new ArrayList<>();
-    private int activeIndex;
-    private int hiddenFloatingFocusIndex = -1;
-    private long version;
-
-    public TerminalWorkspace(AppConfig config) {
-        this.config = config;
-        panes.add(openPane(false));
-    }
-
-    public TerminalPane activePane() {
-        return panes.get(activeIndex);
-    }
-
-    public List<TerminalPane> panes() {
-        List<TerminalPane> visible = panes.stream().filter(TerminalPane::visible).toList();
-        TerminalPane active = activePane();
-        if (!active.visible() || !active.floating()) {
-            return visible;
-        }
-
-        List<TerminalPane> ordered = new ArrayList<>(visible.size());
-        visible.stream()
-                .filter(pane -> pane != active)
-                .forEach(ordered::add);
-        ordered.add(active);
-        return List.copyOf(ordered);
-    }
-
-    public boolean isActive(TerminalPane pane) {
-        return activePane() == pane;
-    }
-
-    public long version() {
-        return version;
-    }
-
-    public void focus(TerminalPane pane) {
-        int index = panes.indexOf(pane);
-        if (index >= 0 && pane.visible() && activeIndex != index) {
-            activeIndex = index;
-            version++;
-        }
-    }
-
-    public void layout(double width, double height) {
-        List<TerminalPane> tiled = panes.stream()
-                .filter(TerminalPane::visible)
-                .filter(pane -> !pane.floating())
-                .toList();
-        int tileCount = Math.max(1, tiled.size());
-        double tileWidth = width / tileCount;
-        for (int i = 0; i < tiled.size(); i++) {
-            tiled.get(i).bounds(i * tileWidth, 0, tileWidth, height);
-        }
-
-        List<TerminalPane> floating = panes.stream()
-                .filter(TerminalPane::visible)
-                .filter(TerminalPane::floating)
-                .toList();
-        for (int i = 0; i < floating.size(); i++) {
-            TerminalPane pane = floating.get(i);
-            if (pane.visible() && pane.floating()) {
-                double floatingWidth = Math.max(420, width * 0.58);
-                double floatingHeight = Math.max(260, height * 0.58);
-                double offset = i * 28.0;
-                pane.bounds(
-                        Math.min(width - floatingWidth - 12.0, ((width - floatingWidth) / 2.0) + offset),
-                        Math.min(height - floatingHeight - 12.0, ((height - floatingHeight) / 2.0) + offset),
-                        floatingWidth,
-                        floatingHeight
-                );
-            }
-        }
-    }
-
-    public void navigate(Direction direction) {
-        TerminalPane current = activePane();
-        if (current.floating() && navigateFloatingStack(direction)) {
-            version++;
-            return;
-        }
-
-        panes.stream()
-                .filter(TerminalPane::visible)
-                .filter(pane -> pane != current)
-                .filter(pane -> directionFilter(direction, current, pane))
-                .min(Comparator.comparingDouble(pane -> distance(current, pane)))
-                .ifPresent(pane -> {
-                    activeIndex = panes.indexOf(pane);
-                    version++;
-                });
-    }
-
-    public void toggleFloating() {
-        List<TerminalPane> floating = panes.stream()
-                .filter(TerminalPane::floating)
-                .toList();
-        if (floating.isEmpty()) {
-            createFloatingPane();
-            return;
-        }
-
-        boolean anyVisible = floating.stream().anyMatch(TerminalPane::visible);
-        if (anyVisible) {
-            TerminalPane active = activePane();
-            hiddenFloatingFocusIndex = active.floating() ? activeIndex : firstVisibleFloatingIndex();
-            floating.forEach(pane -> pane.setVisible(false));
-            activeIndex = firstVisibleNonFloatingIndex();
-            version++;
-        } else {
-            floating.forEach(pane -> pane.setVisible(true));
-            activeIndex = visibleIndexOrFallback(hiddenFloatingFocusIndex, panes.indexOf(floating.get(floating.size() - 1)));
-            hiddenFloatingFocusIndex = -1;
-            version++;
-        }
-    }
-
-    public void createFloatingPane() {
-        TerminalPane pane = openPane(true);
-        panes.add(pane);
-        activeIndex = panes.size() - 1;
-        version++;
-    }
-
-    public void nextFloatingPane() {
-        TerminalPane next = nextFloatingAfter(activeIndex);
-        next.setVisible(true);
-        activeIndex = panes.indexOf(next);
-        version++;
-    }
-
-    public void closeActivePane() {
-        TerminalPane active = activePane();
-        if (!active.floating() || panes.stream().filter(pane -> !pane.floating()).count() == 0) {
-            return;
-        }
-
-        int removed = activeIndex;
-        int previous = previousVisibleIndex(removed);
-        panes.remove(removed);
-        active.close();
-        activeIndex = adjustIndexAfterRemoval(previous, removed);
-        hiddenFloatingFocusIndex = adjustHiddenFocusAfterRemoval(hiddenFloatingFocusIndex, removed);
-        version++;
-    }
-
-    private TerminalPane nextFloatingAfter(int index) {
-        for (int i = index + 1; i < panes.size(); i++) {
-            TerminalPane pane = panes.get(i);
-            if (pane.floating()) {
-                return pane;
-            }
-        }
-        for (int i = 0; i <= index && i < panes.size(); i++) {
-            TerminalPane pane = panes.get(i);
-            if (pane.floating()) {
-                return pane;
-            }
-        }
-        return createAndReturnFloatingPane();
-    }
-
-    private TerminalPane createAndReturnFloatingPane() {
-        TerminalPane pane = openPane(true);
-        panes.add(pane);
-        return pane;
-    }
-
-    private boolean navigateFloatingStack(Direction direction) {
-        List<TerminalPane> floating = panes.stream()
-                .filter(TerminalPane::visible)
-                .filter(TerminalPane::floating)
-                .toList();
-        if (floating.size() < 2) {
-            return false;
-        }
-
-        int current = floating.indexOf(activePane());
-        if (current < 0) {
-            return false;
-        }
-
-        int next = switch (direction) {
-            case LEFT, UP -> current - 1;
-            case DOWN, RIGHT -> current + 1;
-        };
-        if (next < 0 || next >= floating.size()) {
-            return false;
-        }
-
-        activeIndex = panes.indexOf(floating.get(next));
-        return true;
-    }
-
-    private int firstVisibleFloatingIndex() {
-        for (int i = 0; i < panes.size(); i++) {
-            TerminalPane pane = panes.get(i);
-            if (pane.visible() && pane.floating()) {
-                return i;
-            }
-        }
-        return -1;
-    }
-
-    private int firstVisibleNonFloatingIndex() {
-        for (int i = 0; i < panes.size(); i++) {
-            TerminalPane pane = panes.get(i);
-            if (pane.visible() && !pane.floating()) {
-                return i;
-            }
-        }
-        return 0;
-    }
-
-    private int previousVisibleIndex(int index) {
-        for (int i = index - 1; i >= 0; i--) {
-            if (panes.get(i).visible()) {
-                return i;
-            }
-        }
-        for (int i = index + 1; i < panes.size(); i++) {
-            if (panes.get(i).visible()) {
-                return i;
-            }
-        }
-        return firstVisibleNonFloatingIndex();
-    }
-
-    private int visibleIndexOrFallback(int index, int fallback) {
-        if (index >= 0 && index < panes.size() && panes.get(index).visible()) {
-            return index;
-        }
-        return fallback;
-    }
-
-    private static int adjustIndexAfterRemoval(int index, int removedIndex) {
-        if (index < 0) {
-            return 0;
-        }
-        return index > removedIndex ? index - 1 : index;
-    }
-
-    private static int adjustHiddenFocusAfterRemoval(int index, int removedIndex) {
-        if (index < 0 || index == removedIndex) {
-            return -1;
-        }
-        return index > removedIndex ? index - 1 : index;
-    }
-
-    private TerminalPane openPane(boolean floating) {
-        TerminalPane pane = TerminalPane.create(config.columns(), config.rows(), config.maxScrollback());
-        pane.setFloating(floating);
-        pane.attach(ShellSession.start(config.shell(), config.envOverride(), pane, config.columns(), config.rows()));
-        return pane;
-    }
-
-    private static boolean directionFilter(Direction direction, TerminalPane current, TerminalPane candidate) {
-        double currentCenterX = current.x() + current.width() / 2.0;
-        double currentCenterY = current.y() + current.height() / 2.0;
-        double candidateCenterX = candidate.x() + candidate.width() / 2.0;
-        double candidateCenterY = candidate.y() + candidate.height() / 2.0;
-
-        return switch (direction) {
-            case LEFT -> candidateCenterX < currentCenterX;
-            case DOWN -> candidateCenterY > currentCenterY;
-            case UP -> candidateCenterY < currentCenterY;
-            case RIGHT -> candidateCenterX > currentCenterX;
-        };
-    }
-
-    private static double distance(TerminalPane current, TerminalPane candidate) {
-        double dx = (current.x() + current.width() / 2.0) - (candidate.x() + candidate.width() / 2.0);
-        double dy = (current.y() + current.height() / 2.0) - (candidate.y() + candidate.height() / 2.0);
-        return Math.sqrt(dx * dx + dy * dy);
-    }
-
-    @Override
-    public void close() {
-        for (TerminalPane pane : panes) {
-            pane.close();
-        }
-        panes.clear();
-    }
-}