Merge branch 'refactor'

.gitignore

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

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

@@ -0,0 +1,496 @@
+package com.gregor.jprototerm;
+
+import dev.jlibghostty.KeyModifiers;
+import dev.jlibghostty.MouseButton;
+import dev.jlibghostty.MouseEncoderSize;
+import dev.jlibghostty.MouseInput;
+import javafx.geometry.VPos;
+import javafx.scene.canvas.Canvas;
+import javafx.scene.canvas.GraphicsContext;
+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.TextAlignment;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Owns the window's tabs and drives rendering and input. It composites only the current tab:
+ * each frame it lays that tab out, paints the panes bottom-to-top (so the active floating pane
+ * lands on top) and lets each pane paint its own content, clipped to the region the layout gave
+ * it. The cross-pane concerns live here — the dirty-frame bookkeeping, the tab strip, routing
+ * mouse/scroll to the pane under the pointer, and the tab/pane lifecycle that {@link Main}'s key
+ * bindings invoke.
+ */
+public final class Compositor {
+    // Canvas background shown wherever no pane covers (gaps). Painted on a full recomposite.
+    private static final Color GAP_BACKGROUND = Color.rgb(16, 16, 18);
+    private static final Color TAB_TEXT = Color.rgb(225, 229, 235);
+    // Thin tab strip shown at the top when more than one tab is open.
+    private static final double TAB_BAR_HEIGHT = 22.0;
+
+    private final Canvas canvas = new Canvas();
+    private final AppConfig config;
+    private final TerminalMetrics metrics;
+    private final List<Tab> tabs = new ArrayList<>();
+    private int currentTabIndex;
+    // Bumped on any structural change (tab switch, pane add/close/focus/move) so render()
+    // knows to recomposite. Terminal *content* changes are tracked separately through each
+    // tab's content version.
+    private long layoutVersion;
+    // Last content version drawn to the canvas per pane, so a content frame repaints only
+    // the panes that actually changed.
+    private final Map<TerminalPane, Long> paneContentVersion = new HashMap<>();
+    // Cheap per-frame dirty signal: skip the whole render when none of these changed.
+    private double lastWidth = -1.0;
+    private double lastHeight = -1.0;
+    private String lastFontFamily;
+    private double lastFontSize = -1.0;
+    private long lastLayoutVersion = Long.MIN_VALUE;
+    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));
+        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) {
+        metrics.setFont(family, size);
+        paneContentVersion.clear();
+        lastWidth = -1.0; // force a redraw on the next frame
+    }
+
+    // ---- 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)) {
+            layoutVersion++;
+        }
+    }
+
+    public void toggleFloating() {
+        if (isEmpty()) {
+            return;
+        }
+        currentTab().toggleFloating();
+        layoutVersion++;
+    }
+
+    public void createPane() {
+        if (isEmpty()) {
+            return;
+        }
+        currentTab().createPane();
+        layoutVersion++;
+    }
+
+    public void nextFloatingPane() {
+        if (isEmpty()) {
+            return;
+        }
+        currentTab().nextFloatingPane();
+        layoutVersion++;
+    }
+
+    public void closeActivePane() {
+        if (isEmpty()) {
+            return;
+        }
+        currentTab().closeActivePane();
+        if (currentTab().isEmpty()) {
+            // Closing a tab's last pane closes the tab. When no tabs remain the surface is
+            // empty and Main quits.
+            tabs.remove(currentTabIndex);
+            if (currentTabIndex >= tabs.size()) {
+                currentTabIndex = Math.max(0, tabs.size() - 1);
+            }
+        }
+        layoutVersion++;
+    }
+
+    public void newTab() {
+        tabs.add(new Tab(config, metrics));
+        currentTabIndex = tabs.size() - 1;
+        layoutVersion++;
+    }
+
+    public void nextTab() {
+        if (tabs.size() > 1) {
+            currentTabIndex = (currentTabIndex + 1) % tabs.size();
+            layoutVersion++;
+        }
+    }
+
+    public void previousTab() {
+        if (tabs.size() > 1) {
+            currentTabIndex = (currentTabIndex - 1 + tabs.size()) % tabs.size();
+            layoutVersion++;
+        }
+    }
+
+    public void close() {
+        for (Tab tab : tabs) {
+            tab.close();
+        }
+        tabs.clear();
+    }
+
+    private Tab currentTab() {
+        return tabs.get(currentTabIndex);
+    }
+
+    private List<TerminalPane> currentPanes() {
+        return tabs.isEmpty() ? List.of() : currentTab().panes();
+    }
+
+    private boolean isActive(TerminalPane pane) {
+        return !tabs.isEmpty() && currentTab().isActive(pane);
+    }
+
+    private void focus(TerminalPane pane) {
+        if (!tabs.isEmpty() && currentTab().focus(pane)) {
+            layoutVersion++;
+        }
+    }
+
+    // ---- Rendering ------------------------------------------------------------------
+
+    public void render() {
+        switch (nextFrameType()) {
+            case IDLE -> { }
+            case LAYOUT -> renderLayoutFrame();
+            case CONTENT -> renderContentFrame();
+        }
+    }
+
+    // Classify this frame and commit the change trackers. A layout change (size, font,
+    // tab/pane set, z-order, active pane) needs a full recomposite; otherwise a change to the
+    // current tab's content version repaints only the panes that changed; otherwise nothing
+    // changed and the frame is idle.
+    private FrameType nextFrameType() {
+        double width = canvas.getWidth();
+        double height = canvas.getHeight();
+        long contentVersion = tabs.isEmpty() ? 0 : currentTab().contentVersion();
+
+        boolean layoutChanged = width != lastWidth || height != lastHeight
+                || metrics.fontSize() != lastFontSize || !Objects.equals(metrics.fontFamily(), lastFontFamily)
+                || layoutVersion != lastLayoutVersion;
+        boolean contentChanged = contentVersion != lastContentVersion;
+
+        lastWidth = width;
+        lastHeight = height;
+        lastFontFamily = metrics.fontFamily();
+        lastFontSize = metrics.fontSize();
+        lastLayoutVersion = layoutVersion;
+        lastContentVersion = contentVersion;
+
+        if (layoutChanged) {
+            return FrameType.LAYOUT;
+        }
+        if (contentChanged) {
+            return FrameType.CONTENT;
+        }
+        return FrameType.IDLE;
+    }
+
+    // Full recomposite onto the retained canvas: lay the tab out, clear to the gap colour,
+    // draw the tab strip, then paint every pane bottom-to-top (panes() puts the active
+    // floating pane last == on top).
+    private void renderLayoutFrame() {
+        double topInset = tabs.size() > 1 ? TAB_BAR_HEIGHT : 0.0;
+        if (!tabs.isEmpty()) {
+            currentTab().layout(canvas.getWidth(), canvas.getHeight(), topInset);
+        }
+        List<TerminalPane> panes = currentPanes();
+        // Sync each pane's ghostty grid to its (possibly new) bounds; a no-op when unchanged.
+        for (TerminalPane pane : panes) {
+            pane.fitToBounds();
+        }
+
+        GraphicsContext gc = beginFrame();
+        paneContentVersion.keySet().retainAll(panes);
+        gc.setFill(GAP_BACKGROUND);
+        gc.fillRect(0, 0, canvas.getWidth(), canvas.getHeight());
+        if (topInset > 0.0) {
+            drawTabBar(gc, canvas.getWidth(), topInset);
+        }
+        for (TerminalPane pane : panes) {
+            pane.paintFull(gc, isActive(pane));
+            paneContentVersion.put(pane, pane.contentVersion());
+        }
+    }
+
+    // Repaint just the panes whose content changed, directly on the retained canvas. Each pane
+    // clips itself to its rect minus the panes above it, so a lower pane's repaint can't bleed
+    // over one stacked on top — no restore pass needed. Bounds and grids can't have changed
+    // without a layout frame, so a content frame reuses the existing layout untouched.
+    private void renderContentFrame() {
+        List<TerminalPane> panes = currentPanes();
+        GraphicsContext gc = beginFrame();
+
+        for (TerminalPane pane : panes) {
+            Long drawn = paneContentVersion.get(pane);
+            if (drawn != null && drawn == pane.contentVersion()) {
+                continue;
+            }
+            pane.paintIncremental(gc, isActive(pane));
+            paneContentVersion.put(pane, pane.contentVersion());
+        }
+    }
+
+    private GraphicsContext beginFrame() {
+        GraphicsContext gc = canvas.getGraphicsContext2D();
+        gc.setFontSmoothingType(FontSmoothingType.LCD); // the per-cell renderer relies on LCD
+        return gc;
+    }
+
+    // Thin tab strip: one equal-width segment per tab, the current one highlighted, with a
+    // small 1-based number centred in each segment.
+    private void drawTabBar(GraphicsContext gc, double width, double barHeight) {
+        int count = tabs.size();
+        Font barFont = Font.font(metrics.fontFamily(), Math.max(9.0, Math.min(13.0, barHeight * 0.62)));
+        gc.setFont(barFont);
+        gc.setFontSmoothingType(FontSmoothingType.GRAY);
+        gc.setTextAlign(TextAlignment.CENTER);
+        gc.setTextBaseline(VPos.CENTER);
+
+        double gap = 1.0;
+        double segmentWidth = width / count;
+        for (int i = 0; i < count; i++) {
+            double x = i * segmentWidth;
+            boolean current = i == currentTabIndex;
+            gc.setFill(current ? Color.rgb(45, 55, 72) : Color.rgb(22, 24, 28));
+            gc.fillRect(x, 0.0, segmentWidth - gap, barHeight);
+            gc.setFill(current ? TAB_TEXT : Color.rgb(128, 136, 148));
+            gc.fillText(Integer.toString(i + 1), x + (segmentWidth - gap) / 2.0, barHeight / 2.0);
+        }
+
+        // Restore the defaults the cell renderer relies on (left-aligned, baseline, LCD).
+        gc.setTextAlign(TextAlignment.LEFT);
+        gc.setTextBaseline(VPos.BASELINE);
+        gc.setFontSmoothingType(FontSmoothingType.LCD);
+    }
+
+    // ---- Input ----------------------------------------------------------------------
+
+    private void handleMousePressed(MouseEvent event) {
+        canvas.requestFocus();
+        TerminalPane pane = paneAt(event.getX(), event.getY());
+        if (pane == null) {
+            return;
+        }
+
+        focus(pane);
+        pressedButton = mouseButton(event);
+        mouseButtonPressed = true;
+        MouseTarget target = mouseTarget(pane);
+        if (target == null) {
+            return;
+        }
+        send(pane, target, MouseInput.press(pressedButton, localX(event.getX(), pane, target), localY(event.getY(), pane, target), modifiers(event)), true, event);
+    }
+
+    private void handleMouseReleased(MouseEvent event) {
+        TerminalPane pane = paneAt(event.getX(), event.getY());
+        if (pane == null) {
+            pane = activePane();
+        }
+
+        MouseButton button = pressedButton == MouseButton.UNKNOWN ? mouseButton(event) : pressedButton;
+        MouseTarget target = mouseTarget(pane);
+        if (target != null) {
+            send(pane, target, MouseInput.release(button, localX(event.getX(), pane, target), localY(event.getY(), pane, target), 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 = activePane();
+        }
+
+        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(), pane, target), localY(event.getY(), pane, target), modifiers(event)), true, event);
+    }
+
+    private void handleMouseMoved(MouseEvent event) {
+        TerminalPane pane = paneAt(event.getX(), event.getY());
+        if (pane == null) {
+            return;
+        }
+
+        MouseTarget target = mouseTarget(pane);
+        if (target == null) {
+            return;
+        }
+        send(pane, target, MouseInput.motion(localX(event.getX(), pane, target), localY(event.getY(), pane, target), modifiers(event)), mouseButtonPressed, event);
+    }
+
+    private void handleScroll(ScrollEvent event) {
+        TerminalPane pane = paneAt(event.getX(), event.getY());
+        if (pane == null) {
+            return;
+        }
+
+        canvas.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) {
+            // The wheel sends one button press per scrolled row; resolve the position once.
+            double ex = localX(event.getX(), pane, target);
+            double ey = localY(event.getY(), pane, target);
+            KeyModifiers modifiers = modifiers(event);
+            for (int i = 0; i < rows; i++) {
+                sent |= send(pane, target, MouseInput.press(wheelButton, ex, ey, modifiers), mouseButtonPressed, event);
+            }
+        }
+        if (!sent) {
+            // Not consumed by the app (e.g. mouse reporting off): scroll the local viewport.
+            pane.scrollViewport(direction > 0 ? -rows : rows);
+            event.consume();
+        }
+    }
+
+    // Forward an already-positioned mouse event to the pane, consuming it if the pane (i.e.
+    // the app running in it) acted on it. Returns whether it was sent.
+    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 TerminalPane paneAt(double x, double y) {
+        List<TerminalPane> panes = currentPanes();
+        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() <= 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);
+    }
+
+    // Resolve a canvas-space pointer position to a pane-local pixel coordinate, clamped to
+    // the pane's reported screen size (what ghostty's mouse encoder expects).
+    private static double localX(double canvasX, TerminalPane pane, MouseTarget target) {
+        return clamp(canvasX - pane.x() - TerminalMetrics.PADDING, 0.0, target.screenWidth() - 1.0);
+    }
+
+    private static double localY(double canvasY, TerminalPane pane, MouseTarget target) {
+        return clamp(canvasY - pane.y() - 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;
+        };
+    }
+
+    // What one render() pass should do, decided from the change trackers in nextFrame().
+    private enum FrameType {
+        IDLE,     // nothing changed since the last frame
+        LAYOUT,   // geometry/font/tab/pane set changed: clear and repaint everything
+        CONTENT   // only terminal content changed: repaint the panes that changed
+    }
+
+    private record MouseTarget(MouseEncoderSize size, long screenWidth, long screenHeight) {
+    }
+}

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

@@ -0,0 +1,631 @@
+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.scene.canvas.GraphicsContext;
+import javafx.scene.image.Image;
+import javafx.scene.image.PixelFormat;
+import javafx.scene.image.WritableImage;
+import javafx.scene.paint.Color;
+import javafx.scene.text.FontSmoothingType;
+
+import java.io.ByteArrayInputStream;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * The real terminal renderer: paints a pane's background, cell rows, cursor, border, padding
+ * and (when enabled) kitty graphics. One instance per pane, since it caches that pane's
+ * decoded kitty images.
+ */
+final class GhosttyTerminalRenderer extends TerminalRenderer {
+    // GhosttyRenderStateDirty values (stable C ABI; see ghostty/vt/render.h).
+    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);
+    // The default cell background (used for cells with no explicit bg, and as the foreground
+    // for reverse-video cells whose background is the terminal default).
+    private static final Color PANE_BACKGROUND = Color.rgb(9, 10, 12);
+
+    // A full-screen redraw asks for one Color per cell; most cells share a handful of colors,
+    // so cache them by packed RGB instead of allocating a Color each time. Bounded so a
+    // truecolor gradient can't grow it without limit.
+    private static final Map<Integer, Color> COLOR_CACHE = new HashMap<>();
+
+    private final TerminalMetrics metrics;
+    // Decoded kitty images for this renderer's pane (kitty graphics state is per-terminal).
+    private final Map<KittyImageKey, Image> kittyImageCache = new HashMap<>();
+
+    GhosttyTerminalRenderer(TerminalMetrics metrics) {
+        this.metrics = metrics;
+    }
+
+    @Override
+    void paintFull(GraphicsContext gc, RenderTarget target, boolean active) {
+        double px = Math.round(target.x());
+        double py = Math.round(target.y());
+        double width = target.width();
+        double height = target.height();
+        gc.save();
+        clip(gc, px, py, width, height, target.clip());
+        drawContent(gc, target, target.snapshotFull(), px, py, width, height, active,
+                target.kittyEnabled() && hasKittyGraphics(target));
+        gc.restore();
+    }
+
+    @Override
+    void paintIncremental(GraphicsContext gc, RenderTarget target, boolean active) {
+        double px = Math.round(target.x());
+        double py = Math.round(target.y());
+        double width = target.width();
+        double height = target.height();
+        gc.save();
+        clip(gc, px, py, width, height, target.clip());
+        if (target.kittyEnabled() && hasKittyGraphics(target)) {
+            // Kitty placements can move without a per-row dirty flag, so always redraw whole.
+            drawContent(gc, target, target.snapshotFull(), px, py, width, height, active, true);
+        } else {
+            RenderStateSnapshot snapshot = target.snapshot();
+            int dirty = snapshot == null ? DIRTY_FULL : snapshot.dirty();
+            if (dirty == DIRTY_FULL) {
+                drawContent(gc, target, snapshot, px, py, width, height, active, false);
+            } else if (dirty == DIRTY_PARTIAL) {
+                drawDirtyRows(gc, snapshot, px, py, width, height, active);
+            }
+            // dirty == FALSE: nothing visible changed.
+        }
+        gc.restore();
+    }
+
+    // Full content render: background, border, all rows, cursor, and (when enabled) kitty
+    // graphics. Used by the kitty direct path and by full redraws.
+    private void drawContent(
+            GraphicsContext gc,
+            RenderTarget target,
+            RenderStateSnapshot snapshot,
+            double x,
+            double y,
+            double width,
+            double height,
+            boolean active,
+            boolean withKitty
+    ) {
+        double cellWidth = metrics.cellWidth();
+        double lineHeight = metrics.lineHeight();
+        gc.setFontSmoothingType(FontSmoothingType.LCD);
+        gc.setFill(PANE_BACKGROUND);
+        gc.fillRect(x, y, width, height);
+        gc.setFont(metrics.font());
+
+        double left = x + TerminalMetrics.PADDING;
+        double top = y + TerminalMetrics.PADDING;
+        double baseline = top + metrics.baselineOffset();
+
+        Map<KittyPlaceholderKey, KittyPlaceholderBounds> placeholderBounds = withKitty
+                ? kittyPlaceholderBounds(snapshot)
+                : Map.of();
+
+        if (withKitty) {
+            drawKittyGraphics(gc, target, KittyPlacementLayer.BELOW_TEXT, placeholderBounds, left, top, cellWidth, lineHeight);
+        }
+
+        if (snapshot != null) {
+            double contentBottom = top + snapshot.rows() * lineHeight;
+            fillVerticalPadding(gc, snapshot, x, y, width, height, top, contentBottom);
+            for (RenderRow row : snapshot.renderRows()) {
+                double y0 = Math.floor(top + (row.row() * lineHeight));
+                double y1 = Math.ceil(top + ((row.row() + 1) * lineHeight));
+                paintSidePadding(gc, row, x, width, left, cellWidth, y0, y1 - y0);
+                drawRow(gc, row, left, top, baseline, cellWidth, lineHeight);
+            }
+            drawCursor(gc, snapshot, left, top, cellWidth, lineHeight);
+        }
+
+        if (withKitty) {
+            drawKittyGraphics(gc, target, KittyPlacementLayer.ABOVE_TEXT, placeholderBounds, left, top, cellWidth, lineHeight);
+        }
+
+        drawBorder(gc, x, y, width, height, active);
+    }
+
+    // Incremental render: repaint only the rows ghostty flagged dirty, then restore the
+    // cursor and border. The local band tracks the repainted span only so the border redraw
+    // can be limited to it.
+    private void drawDirtyRows(
+            GraphicsContext gc,
+            RenderStateSnapshot snapshot,
+            double px,
+            double py,
+            double pw,
+            double ph,
+            boolean active
+    ) {
+        double cellWidth = metrics.cellWidth();
+        double lineHeight = metrics.lineHeight();
+        gc.setFontSmoothingType(FontSmoothingType.LCD);
+        gc.setFont(metrics.font());
+        double left = px + TerminalMetrics.PADDING;
+        double top = py + TerminalMetrics.PADDING;
+        double baseline = top + metrics.baselineOffset();
+
+        double contentBottom = top + snapshot.rows() * lineHeight;
+        int lastRow = snapshot.rows() - 1;
+        boolean cursorRowDirty = false;
+        double bandMin = Double.POSITIVE_INFINITY;
+        double bandMax = Double.NEGATIVE_INFINITY;
+        for (RenderRow row : snapshot.renderRows()) {
+            if (!row.dirty()) {
+                continue;
+            }
+            // Snap the row band to integer pixels and paint opaque: a fractional-height fill
+            // would leave sub-pixel seams between rows.
+            double y0 = Math.floor(top + (row.row() * lineHeight));
+            double y1 = Math.ceil(top + ((row.row() + 1) * lineHeight));
+            gc.setFill(PANE_BACKGROUND);
+            gc.fillRect(px, y0, pw, y1 - y0);
+            paintSidePadding(gc, row, px, pw, left, cellWidth, y0, y1 - y0);
+            drawRow(gc, row, left, top, baseline, cellWidth, lineHeight);
+            bandMin = Math.min(bandMin, y0);
+            bandMax = Math.max(bandMax, y1);
+            // Edge rows also own the top/bottom padding strip; repaint it and extend the
+            // band so panes stacked above get restored over it too.
+            if (row.row() == 0) {
+                gc.setFill(rowEdgeBackground(row, true));
+                gc.fillRect(px, py, pw, top - py);
+                bandMin = Math.min(bandMin, py);
+            }
+            if (row.row() == lastRow) {
+                gc.setFill(rowEdgeBackground(row, true));
+                gc.fillRect(px, contentBottom, pw, py + ph - contentBottom);
+                bandMax = Math.max(bandMax, py + ph);
+            }
+            if (snapshot.cursorViewportHasValue() && row.row() == snapshot.cursorViewportY()) {
+                cursorRowDirty = true;
+            }
+        }
+        if (bandMin > bandMax) {
+            return;
+        }
+
+        // The cursor overlays its cell; redraw it only when its row was repainted, so we
+        // neither leave a stale cursor nor stack the translucent overlay on itself.
+        if (cursorRowDirty) {
+            drawCursor(gc, snapshot, left, top, cellWidth, lineHeight);
+        }
+        // Repainting rows clears the side borders within the band; restore just those
+        // segments, clipped to the band so we don't redraw the whole outline.
+        gc.save();
+        clipRect(gc, px, bandMin, pw, bandMax - bandMin);
+        drawBorder(gc, px, py, pw, ph, active);
+        gc.restore();
+    }
+
+    private void drawBorder(GraphicsContext gc, double x, double y, double width, double height, boolean active) {
+        gc.setStroke(active ? Color.rgb(87, 166, 255) : Color.rgb(52, 57, 65));
+        gc.setLineWidth(active ? 2.0 : 1.0);
+        gc.strokeRect(x + 0.5, y + 0.5, width - 1.0, height - 1.0);
+    }
+
+    // Effective background colour of a cell as it is drawn (reverse video swaps fg/bg, an
+    // unset colour falls back to the defaults).
+    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));
+    }
+
+    // Extend the row's edge-cell backgrounds into the left/right padding (the margin and the
+    // right-edge rounding sliver), so the unused space matches the rendered content.
+    private void paintSidePadding(GraphicsContext gc, RenderRow row, double paneX, double paneWidth,
+            double contentLeft, double cellWidth, double yTop, double bandHeight) {
+        int columns = row.cells().size();
+        if (columns == 0) {
+            return;
+        }
+        double contentRight = contentLeft + (columns * cellWidth);
+        gc.setFill(rowEdgeBackground(row, true));
+        gc.fillRect(paneX, yTop, contentLeft - paneX, bandHeight);
+        gc.setFill(rowEdgeBackground(row, false));
+        gc.fillRect(contentRight, yTop, paneX + paneWidth - contentRight, bandHeight);
+    }
+
+    // Fill the top/bottom padding strips with the top/bottom row's edge colour.
+    private void fillVerticalPadding(GraphicsContext gc, RenderStateSnapshot snapshot,
+            double paneX, double paneY, double paneWidth, double paneHeight, double contentTop, double contentBottom) {
+        List<RenderRow> rows = snapshot.renderRows();
+        if (rows.isEmpty()) {
+            return;
+        }
+        gc.setFill(rowEdgeBackground(rows.get(0), true));
+        gc.fillRect(paneX, paneY, paneWidth, contentTop - paneY);
+        gc.setFill(rowEdgeBackground(rows.get(rows.size() - 1), true));
+        gc.fillRect(paneX, contentBottom, paneWidth, paneY + paneHeight - contentBottom);
+    }
+
+    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);
+
+            // Resolve fg/bg (null bg = terminal default, painted by the pane background).
+            // Avoid Optional.map's allocation on this hot path.
+            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;
+
+            // Reverse video: ghostty does not bake inverse into the resolved colours, so we
+            // swap them here, falling back to the terminal defaults for whichever is unset.
+            if (cell.inverse()) {
+                Color swappedBg = fg;
+                fg = (bg != null) ? bg : PANE_BACKGROUND;
+                bg = swappedBg;
+            }
+
+            if (bg != null) {
+                gc.setFill(bg);
+                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);
+            gc.setFill(fg);
+            gc.fillText(cell.text(), x, y);
+        }
+    }
+
+    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 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));
+        }
+    }
+
+    // ---- Kitty graphics --------------------------------------------------------------
+
+    private static boolean hasKittyGraphics(RenderTarget target) {
+        return target.kittyGraphics()
+                .map(graphics -> !graphics.placements().isEmpty())
+                .orElse(false);
+    }
+
+    private void drawKittyGraphics(
+            GraphicsContext gc,
+            RenderTarget target,
+            KittyPlacementLayer layer,
+            Map<KittyPlaceholderKey, KittyPlaceholderBounds> placeholderBounds,
+            double originX,
+            double originY,
+            double cellWidth,
+            double lineHeight
+    ) {
+        target.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 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) {
+        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;
+    }
+
+    // A kitty image is immutable for a given (id, number); re-transmitting under the same id
+    // changes the number (and the snapshot below evicts stale entries by id anyway). So the
+    // identity + dimensions + payload length are enough to key the decoded-image cache, and
+    // we avoid fingerprinting the whole payload — which previously ran once per frame per
+    // placement (O(image size)) just to look the image up.
+    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 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/Main.java

@@ -21,20 +21,20 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 
 public final class Main extends Application {
-    private TerminalWorkspace workspace;
+    private Compositor compositor;
-    private TerminalCanvasView terminalView;
+    private TerminalMetrics metrics;
     private AppConfig config;
 
     @Override
     public void start(Stage stage) {
         config = AppConfig.load();
 
-        workspace = new TerminalWorkspace(config);
+        metrics = new TerminalMetrics(config.fontFamily(), config.fontSize());
-        terminalView = new TerminalCanvasView(workspace, config);
+        compositor = new Compositor(config, metrics);
 
-        StackPane root = new StackPane(terminalView.canvas());
+        StackPane root = new StackPane(compositor.canvas());
-        terminalView.canvas().widthProperty().bind(root.widthProperty());
+        compositor.canvas().widthProperty().bind(root.widthProperty());
-        terminalView.canvas().heightProperty().bind(root.heightProperty());
+        compositor.canvas().heightProperty().bind(root.heightProperty());
 
         Scene scene = new Scene(root, config.windowWidth(), config.windowHeight());
         scene.addEventFilter(KeyEvent.KEY_PRESSED, this::handlePressed);
@@ -43,57 +43,57 @@ public final class Main extends Application {
         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.canvas().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_pane").matches(event)) {
-            workspace.createPane();
+            compositor.createPane();
             event.consume();
         } else if (config.keybindings().get("next_floating").matches(event)) {
-            workspace.nextFloatingPane();
+            compositor.nextFloatingPane();
             event.consume();
         } else if (config.keybindings().get("close_pane").matches(event)) {
-            workspace.closeActivePane();
+            compositor.closeActivePane();
             event.consume();
-            if (workspace.isEmpty()) {
+            if (compositor.isEmpty()) {
                 // Closing the last pane quits the app.
-                workspace.close();
+                compositor.close();
                 Platform.exit();
             }
         } else if (config.keybindings().get("new_tab").matches(event)) {
-            workspace.newTab();
+            compositor.newTab();
             event.consume();
         } else if (config.keybindings().get("previous_tab").matches(event)) {
-            workspace.previousTab();
+            compositor.previousTab();
             event.consume();
         } else if (config.keybindings().get("next_tab").matches(event)) {
-            workspace.nextTab();
+            compositor.nextTab();
             event.consume();
         } else if (config.keybindings().get("open_font_selector").matches(event)) {
             openFontSelector();
@@ -104,7 +104,7 @@ 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();
             }
         }
@@ -117,7 +117,7 @@ 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();
         }
     }
@@ -160,18 +160,18 @@ public final class Main extends Application {
                     double selectedSize = size.getValue();
                     config = config.withFont(selectedFamily.trim(), selectedSize);
                     config.save();
-                    terminalView.setFont(config.fontFamily(), config.fontSize());
+                    compositor.setFont(config.fontFamily(), config.fontSize());
-                    terminalView.canvas().requestFocus();
+                    compositor.canvas().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/RenderTarget.java

@@ -0,0 +1,45 @@
+package com.gregor.jprototerm;
+
+import dev.jlibghostty.KittyGraphics;
+import dev.jlibghostty.RenderStateSnapshot;
+import javafx.scene.shape.Shape;
+
+import java.util.Optional;
+
+/**
+ * The read-only view of a pane that a {@link TerminalRenderer} draws: its on-screen rect, its
+ * current render snapshot, and its kitty-graphics state. Decoupling the renderer from
+ * {@link TerminalPane} through this interface lets the renderer be swapped (e.g. a debug
+ * renderer that just outlines bounds and clip bands) and unit-tested against a synthetic
+ * target without a real terminal.
+ */
+interface RenderTarget {
+    double x();
+
+    double y();
+
+    double width();
+
+    double height();
+
+    /** Whether kitty graphics should be drawn for this target at all. */
+    boolean kittyEnabled();
+
+    Optional<KittyGraphics> kittyGraphics();
+
+    /**
+     * Incremental snapshot: only rows that changed since the last frame are populated. May be
+     * {@code null} before the first snapshot exists.
+     */
+    RenderStateSnapshot snapshot();
+
+    /** Full snapshot with every row populated, regardless of dirty state. */
+    RenderStateSnapshot snapshotFull();
+
+    /**
+     * The region this target may draw into, or {@code null} to clip to its plain rect. Set at
+     * layout time (a tiled pane gets its rect minus the floating panes that cover it), so the
+     * renderer can clip its own output and never paint over a pane on top.
+     */
+    Shape clip();
+}

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

@@ -1,262 +1,276 @@
 package com.gregor.jprototerm;
 
+import javafx.scene.shape.Rectangle;
+import javafx.scene.shape.Shape;
+
 import java.util.ArrayList;
 import java.util.Comparator;
 import java.util.List;
+import java.util.stream.Stream;
 
 /**
- * One tab: an isolated stack of panes (tiled + floating) with its own active pane and
+ * One tab: a row of tiled panes with a group of floating panes shown over them. Floating panes
- * stashed-floating state. {@link TerminalWorkspace} owns the list of tabs and renders only
+ * are shown/hidden as a group ({@code floatingVisible}), and there is always at least one tiled
- * the current one. Mutating methods return whether they actually changed anything so the
+ * pane — a floating pane is promoted if the last tiled one closes — so the layout always has a
- * workspace can bump its render version conditionally.
+ * 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 List<TerminalPane> panes = new ArrayList<>();
+    private final TerminalMetrics metrics;
-    private int activeIndex;
+    private final List<TerminalPane> tiled = new ArrayList<>();
-    private int hiddenFloatingFocusIndex = -1;
+    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) {
+    Tab(AppConfig config, TerminalMetrics metrics) {
         this.config = config;
-        panes.add(openPane(false));
+        this.metrics = metrics;
+        this.lastWidth = config.windowWidth();
+        this.lastHeight = config.windowHeight();
+        TerminalPane first = openPane(false);
+        tiled.add(first);
+        active = first;
     }
 
     TerminalPane activePane() {
-        return panes.get(activeIndex);
+        return active;
     }
 
     boolean isEmpty() {
-        return panes.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 (panes.isEmpty()) {
+        if (!floatingVisible || floating.isEmpty()) {
-            return List.of();
+            return List.copyOf(tiled);
         }
-        List<TerminalPane> visible = panes.stream().filter(TerminalPane::visible).toList();
+        List<TerminalPane> ordered = new ArrayList<>(tiled.size() + floating.size());
-        if (visible.isEmpty()) {
+        ordered.addAll(tiled);
-            return List.of();
+        for (TerminalPane pane : floating) {
-        }
+            if (pane != active) {
-        // Draw order = z-order: all tiled panes first (they never overlap), then floating
-        // panes on top, with the active floating pane last (topmost). This holds regardless
-        // of creation order, so a tiled pane created after a floating one still sits behind.
-        TerminalPane active = activePane();
-        List<TerminalPane> ordered = new ArrayList<>(visible.size());
-        for (TerminalPane pane : visible) {
-            if (!pane.floating()) {
                 ordered.add(pane);
             }
         }
-        for (TerminalPane pane : visible) {
+        if (floating.contains(active)) {
-            if (pane.floating() && pane != active) {
+            ordered.add(active); // active floating pane on top
-                ordered.add(pane);
-            }
-        }
-        if (active.visible() && active.floating()) {
-            ordered.add(active);
         }
         return List.copyOf(ordered);
     }
 
     boolean isActive(TerminalPane pane) {
-        return !panes.isEmpty() && activePane() == pane;
+        return pane != null && pane == active;
     }
 
     boolean focus(TerminalPane pane) {
-        int index = panes.indexOf(pane);
+        if (pane == active || !isFocusable(pane)) {
-        if (index >= 0 && pane.visible() && activeIndex != index) {
-            setActive(index);
-            return true;
-        }
             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;
-        List<TerminalPane> tiled = panes.stream()
+
-                .filter(TerminalPane::visible)
+        double tileWidth = width / Math.max(1, tiled.size());
-                .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, topInset, tileWidth, availHeight);
         }
 
-        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);
         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;
-            pane.bounds(
+            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
+                    floatingHeight);
-            );
         }
+
+        assignClips();
+    }
+
+    // Give each pane its clip region for the next paints, so repainting a pane on a content
+    // frame can never bleed over one stacked on top of it. Each pane is clipped to its rect
+    // minus the union of the panes above it: floating panes are clipped by the floating panes
+    // higher in the stack, and tiled panes by the whole floating group. When nothing floats,
+    // every pane clips to its plain bounds.
+    private void assignClips() {
+        if (!floatingVisible || floating.isEmpty()) {
+            tiled.forEach(pane -> pane.setClip(null));
+            floating.forEach(pane -> pane.setClip(null));
+            return;
+        }
+
+        // Floating panes bottom-to-top, matching panes(): insertion order, active pane on top.
+        List<TerminalPane> order = new ArrayList<>(floating.size());
+        for (TerminalPane pane : floating) {
+            if (pane != active) {
+                order.add(pane);
+            }
+        }
+        if (floating.contains(active)) {
+            order.add(active);
+        }
+
+        // Walk top-to-bottom, accumulating the union of the panes above each one.
+        Shape above = null;
+        for (int i = order.size() - 1; i >= 0; i--) {
+            Rectangle rect = rectOf(order.get(i));
+            order.get(i).setClip(above == null ? null : Shape.subtract(rect, above));
+            above = (above == null) ? rect : Shape.union(above, rect);
+        }
+
+        // `above` is now the union of every floating pane; tiled panes sit under all of them.
+        for (TerminalPane pane : tiled) {
+            pane.setClip(Shape.subtract(rectOf(pane), above));
+        }
+    }
+
+    // Match the renderer's pixel snapping (round the origin, keep width/height) so the clip
+    // lines up exactly with where the floating panes are drawn.
+    private static Rectangle rectOf(TerminalPane pane) {
+        return new Rectangle(Math.round(pane.x()), Math.round(pane.y()), pane.width(), pane.height());
     }
 
     boolean navigate(Direction direction) {
-        TerminalPane current = activePane();
+        if (floating.contains(active) && navigateFloatingStack(direction)) {
-        if (current.floating() && navigateFloatingStack(direction)) {
             return true;
         }
-
+        TerminalPane target = focusable()
-        TerminalPane target = panes.stream()
+                .filter(pane -> pane != active)
-                .filter(TerminalPane::visible)
+                .filter(pane -> directionFilter(direction, active, pane))
-                .filter(pane -> pane != current)
+                .min(Comparator.comparingDouble(pane -> distance(active, pane)))
-                .filter(pane -> directionFilter(direction, current, pane))
-                .min(Comparator.comparingDouble(pane -> distance(current, pane)))
                 .orElse(null);
         if (target != null) {
-            setActive(panes.indexOf(target));
+            setActive(target);
             return true;
         }
         return false;
     }
 
     void toggleFloating() {
-        List<TerminalPane> floating = panes.stream()
-                .filter(TerminalPane::floating)
-                .toList();
         if (floating.isEmpty()) {
             createFloatingPane();
             return;
         }
-
+        if (floatingVisible) {
-        boolean anyVisible = floating.stream().anyMatch(TerminalPane::visible);
+            floatingVisible = false;
-        if (anyVisible) {
+            if (floating.contains(active)) {
-            TerminalPane active = activePane();
+                setActive(tiled.get(0));
-            hiddenFloatingFocusIndex = active.floating() ? activeIndex : firstVisibleFloatingIndex();
+            }
-            floating.forEach(pane -> pane.setVisible(false));
-            setActive(firstVisibleNonFloatingIndex());
         } else {
-            floating.forEach(pane -> pane.setVisible(true));
+            floatingVisible = true;
-            setActive(visibleIndexOrFallback(hiddenFloatingFocusIndex, panes.indexOf(floating.get(floating.size() - 1))));
+            setActive(floating.contains(lastFocusedFloating) ? lastFocusedFloating : floating.get(floating.size() - 1));
-            hiddenFloatingFocusIndex = -1;
         }
     }
 
-    /**
+    /** Adds a floating pane while the floating group is shown, otherwise a tiled pane. */
-     * "New pane": adds a floating pane while floating panes are shown, otherwise adds a
-     * tiled pane (the tiled row is redistributed equally by the layout).
-     */
     void createPane() {
-        if (anyFloatingVisible()) {
+        if (floatingVisible) {
             createFloatingPane();
         } else {
             TerminalPane pane = openPane(false);
-            panes.add(pane);
+            tiled.add(pane);
-            setActive(panes.size() - 1);
+            setActive(pane);
         }
     }
 
     void nextFloatingPane() {
-        TerminalPane next = nextFloatingAfter(activeIndex);
+        if (floating.isEmpty()) {
-        next.setVisible(true);
+            createFloatingPane();
-        setActive(panes.indexOf(next));
+            return;
+        }
+        floatingVisible = true;
+        int current = floating.indexOf(active); // -1 when the active pane is tiled
+        setActive(floating.get((current + 1 + floating.size()) % floating.size()));
     }
 
     void closeActivePane() {
-        TerminalPane active = activePane();
+        TerminalPane closing = active;
-        int removed = activeIndex;
+        boolean wasFloating = floating.remove(closing);
-        // When closing a floating pane, focus the next visible floating pane if there is one
+        if (!wasFloating) {
-        // (don't jump to a tiled pane); otherwise fall back to the nearest visible pane.
+            tiled.remove(closing);
-        int target = active.floating() ? nearestVisibleFloatingIndex(removed) : -1;
-        if (target < 0) {
-            target = previousVisibleIndex(removed);
         }
-        panes.remove(removed);
+        if (closing == lastFocusedFloating) {
-        if (active == lastFocusedFloating) {
             lastFocusedFloating = null;
         }
-        active.close();
+        closing.close();
-        if (panes.isEmpty()) {
+
-            activeIndex = 0;
+        if (tiled.isEmpty() && floating.isEmpty()) {
+            active = null; // tab is now empty; the compositor drops it
             return;
         }
-        activeIndex = adjustIndexAfterRemoval(target, removed);
-        hiddenFloatingFocusIndex = adjustHiddenFocusAfterRemoval(hiddenFloatingFocusIndex, removed);
 
-        // If the last tiled (main) pane was closed, promote a floating pane to be the new
+        // Always keep a tiled base: if the last tiled pane just closed, promote a floating one
-        // main pane so the layout has a base and rendering continues normally. Prefer the
+        // (preferring the last focused).
-        // most recently focused floating pane.
+        if (tiled.isEmpty()) {
-        if (panes.stream().noneMatch(pane -> !pane.floating())) {
+            TerminalPane promote = floating.contains(lastFocusedFloating) ? lastFocusedFloating : floating.get(0);
-            TerminalPane promote = (lastFocusedFloating != null && panes.contains(lastFocusedFloating))
+            var promoteIndex = floating.indexOf(promote);
-                    ? lastFocusedFloating
+            var nextFocussed = promoteIndex == 0 ? 0 : promoteIndex - 1;
-                    : panes.get(activeIndex);
+            floating.remove(promote);
-            promote.setFloating(false);
+            tiled.add(promote);
-            promote.setVisible(true);
+            if (promote == lastFocusedFloating) {
-            activeIndex = panes.indexOf(promote);
                 lastFocusedFloating = null;
+                if (!floating.isEmpty()) {
+                    lastFocusedFloating = floating.isEmpty() ? null : floating.get(nextFocussed);
+                }
+            }
+        }
+        if (floating.isEmpty()) {
+            floatingVisible = false;
         }
 
-        // If only hidden panes remained, reveal the one we're focusing so the screen isn't
+        setActive(wasFloating && floatingVisible ? floating.get(floating.size() - 1) : tiled.get(0));
-        // blank.
-        if (!panes.get(activeIndex).visible()) {
-            panes.get(activeIndex).setVisible(true);
-        }
     }
 
-    private void setActive(int index) {
+    private void setActive(TerminalPane pane) {
-        activeIndex = index;
+        active = pane;
-        if (index >= 0 && index < panes.size() && panes.get(index).floating()) {
+        if (floating.contains(pane)) {
-            lastFocusedFloating = panes.get(index);
+            lastFocusedFloating = pane;
         }
     }
 
     private void createFloatingPane() {
         TerminalPane pane = openPane(true);
-        panes.add(pane);
+        floating.add(pane);
-        setActive(panes.size() - 1);
+        floatingVisible = true;
-    }
+        setActive(pane);
-
-    private boolean anyFloatingVisible() {
-        return panes.stream().anyMatch(pane -> pane.floating() && pane.visible());
-    }
-
-    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(active);
-        int current = floating.indexOf(activePane());
         if (current < 0) {
             return false;
         }
-
         int next = switch (direction) {
             case LEFT, UP -> current - 1;
             case DOWN, RIGHT -> current + 1;
@@ -264,85 +278,35 @@ final class Tab implements AutoCloseable {
         if (next < 0 || next >= floating.size()) {
             return false;
         }
-
+        setActive(floating.get(next));
-        setActive(panes.indexOf(floating.get(next)));
         return true;
     }
 
-    private int firstVisibleFloatingIndex() {
+    private boolean isFocusable(TerminalPane pane) {
-        for (int i = 0; i < panes.size(); i++) {
+        return tiled.contains(pane) || (floatingVisible && floating.contains(pane));
-            TerminalPane pane = panes.get(i);
-            if (pane.visible() && pane.floating()) {
-                return i;
-            }
-        }
-        return -1;
     }
 
-    private int firstVisibleNonFloatingIndex() {
+    private Stream<TerminalPane> focusable() {
-        for (int i = 0; i < panes.size(); i++) {
+        return floatingVisible ? Stream.concat(tiled.stream(), floating.stream()) : tiled.stream();
-            TerminalPane pane = panes.get(i);
-            if (pane.visible() && !pane.floating()) {
-                return i;
-            }
-        }
-        return 0;
     }
 
-    private int nearestVisibleFloatingIndex(int index) {
+    private void markContentChanged() {
-        for (int i = index + 1; i < panes.size(); i++) {
+        contentVersion++;
-            if (panes.get(i).visible() && panes.get(i).floating()) {
-                return i;
-            }
-        }
-        for (int i = index - 1; i >= 0; i--) {
-            if (panes.get(i).visible() && panes.get(i).floating()) {
-                return i;
-            }
-        }
-        return -1;
     }
 
-    private int previousVisibleIndex(int index) {
+    private TerminalPane openPane(boolean asFloating) {
-        for (int i = index - 1; i >= 0; i--) {
+        double availHeight = lastHeight - lastTopInset;
-            if (panes.get(i).visible()) {
+        double widthPx;
-                return i;
+        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);
-        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) {
@@ -367,9 +331,9 @@ final class Tab implements AutoCloseable {
 
     @Override
     public void close() {
-        for (TerminalPane pane : panes) {
+        tiled.forEach(TerminalPane::close);
-            pane.close();
+        floating.forEach(TerminalPane::close);
-        }
+        tiled.clear();
-        panes.clear();
+        floating.clear();
     }
 }

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

@@ -1,35 +1,46 @@
 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 javafx.scene.canvas.GraphicsContext;
+import javafx.scene.shape.Shape;
 
 import java.util.Optional;
-import java.util.concurrent.atomic.AtomicLong;
-
-public final class TerminalPane implements AutoCloseable {
-    // Monotonic across all panes, bumped on every content change. Lets the renderer detect
-    // "nothing changed" in O(1) without scanning panes or building a render key.
-    private static final AtomicLong RENDER_TICK = new AtomicLong();
-
-    public static long renderTick() {
-        return RENDER_TICK.get();
-    }
 
+/**
+ * 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 — it is a {@link RenderTarget}
+ * that a {@link TerminalRenderer} paints. {@link #paintFull}/{@link #paintIncremental} are the
+ * only rendering API exposed to the {@link Compositor}, and they just delegate to that
+ * renderer; the compositor decides z-order and which rect each pane occupies.
+ */
+public final class TerminalPane implements AutoCloseable, RenderTarget {
     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 TerminalRenderer renderer;
     private final MouseEncoder mouseEncoder = new MouseEncoder();
+    // 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;
+    // Clip region for rendering (rect minus the panes covering this one), set at layout time;
-    private boolean visible = true;
+    // null means clip to the plain bounds. See RenderTarget#clip().
+    private Shape clip;
     private double x;
     private double y;
     private double width;
@@ -38,47 +49,40 @@ public final class TerminalPane implements AutoCloseable {
     private int rows;
     private int pixelWidth;
     private int pixelHeight;
-    // Bumped on the reader thread (terminal writes) and read on the FX thread (render loop),
+    private long contentVersion;
-    // so it must be volatile.
-    private volatile long renderVersion;
     private long snapshotVersion = -1;
-    private volatile boolean closed;
 
-    private TerminalPane(Terminal terminal, int columns, int rows) {
+    private TerminalPane(Terminal terminal, TerminalMetrics metrics, boolean kittyEnabled,
+            Runnable onContentChange, TerminalRenderer renderer, int columns, int rows) {
         this.terminal = terminal;
+        this.metrics = metrics;
+        this.kittyEnabled = kittyEnabled;
+        this.onContentChange = onContentChange;
+        this.renderer = renderer;
         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,
+                new GhosttyTerminalRenderer(metrics), columns, rows);
         pane.refresh();
+        pane.attach(ShellSession.start(config.shell(), config.envOverride(), pane, columns, rows));
         return pane;
     }
 
-    public void write(String text) {
+    private void attach(ShellSession session) {
-        synchronized (terminal) {
-            if (closed) {
-                return;
-            }
-            terminal.write(text);
-            refresh();
-        }
-    }
-
-    public void write(byte[] bytes) {
-        synchronized (terminal) {
-            if (closed) {
-                return;
-            }
-            terminal.write(bytes);
-            refresh();
-        }
-    }
-
-    public void attach(ShellSession session) {
         this.session = session;
         terminal.setPtyWriter(bytes -> {
             ShellSession current = this.session;
@@ -89,6 +93,20 @@ public final class TerminalPane implements AutoCloseable {
         session.startReading(this);
     }
 
+    public void write(String text) {
+        synchronized (terminal) {
+            terminal.write(text);
+            refresh();
+        }
+    }
+
+    public void write(byte[] bytes) {
+        synchronized (terminal) {
+            terminal.write(bytes);
+            refresh();
+        }
+    }
+
     public void send(String text) {
         scrollViewportToBottom();
         if (session != null) {
@@ -122,7 +140,7 @@ public final class TerminalPane implements AutoCloseable {
         }
     }
 
-    public void scrollViewportToBottom() {
+    private void scrollViewportToBottom() {
         synchronized (terminal) {
             terminal.scrollViewport(ScrollViewport.bottom());
             refresh();
@@ -130,16 +148,37 @@ public final class TerminalPane implements AutoCloseable {
     }
 
     /**
-     * Full render snapshot of the current screen, memoised per content version (so a burst
+     * Incremental snapshot: cells are marshalled only for rows that changed since the last
-     * of writes between two frames yields one snapshot). Uses a throwaway render state per
+     * frame (global dirty == PARTIAL), reused across calls for the same content version.
-     * snapshot, which always returns the complete, correct screen — a persistent render
+     * Snapshotting is deferred here rather than done in refresh(), so a burst of writes
-     * state's per-row dirty tracking proved unreliable across resizes and screen clears.
+     * between two frames collapses into a single snapshot.
      */
-    public RenderStateSnapshot renderSnapshot() {
+    @Override
+    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).
+     */
+    @Override
+    public RenderStateSnapshot snapshotFull() {
+        return takeSnapshot(true);
+    }
+
+    private RenderStateSnapshot takeSnapshot(boolean full) {
         synchronized (terminal) {
-            if (snapshotVersion != renderVersion) {
+            if (full) {
-                cachedSnapshot = terminal.renderSnapshot();
+                renderState.update(terminal);
-                snapshotVersion = renderVersion;
+                cachedSnapshot = renderState.snapshot();
+                renderState.resetDirty();
+                snapshotVersion = contentVersion;
+            } else if (snapshotVersion != contentVersion) {
+                renderState.update(terminal);
+                cachedSnapshot = renderState.snapshotIncremental();
+                renderState.resetDirty();
+                snapshotVersion = contentVersion;
             }
             return cachedSnapshot;
         }
@@ -151,44 +190,39 @@ public final class TerminalPane implements AutoCloseable {
         }
     }
 
-    public long renderVersion() {
+    /** This pane's own content revision, bumped on every change (see {@link #refresh()}). */
-        return renderVersion;
+    public long contentVersion() {
+        return contentVersion;
     }
 
+    @Override
+    public boolean kittyEnabled() {
+        return kittyEnabled;
+    }
+
+    @Override
     public Optional<KittyGraphics> kittyGraphics() {
         synchronized (terminal) {
             return terminal.kittyGraphics();
         }
     }
 
-    public boolean floating() {
+    @Override
-        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;
     }
 
+    @Override
     public double y() {
         return y;
     }
 
+    @Override
     public double width() {
         return width;
     }
 
+    @Override
     public double height() {
         return height;
     }
@@ -200,7 +234,24 @@ public final class TerminalPane implements AutoCloseable {
         this.height = height;
     }
 
-    public void resize(int columns, int rows, int pixelWidth, int pixelHeight) {
+    /** Set the clip region applied on the next paints (see {@link RenderTarget#clip()}). */
+    public void setClip(Shape clip) {
+        this.clip = clip;
+    }
+
+    @Override
+    public Shape clip() {
+        return clip;
+    }
+
+    /** 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;
         }
@@ -222,26 +273,31 @@ public final class TerminalPane implements AutoCloseable {
     }
 
     private void refresh() {
-        // Only mark the pane dirty; the snapshot itself is computed lazily in
+        // Mark this pane's content dirty (the snapshot is computed lazily in the paint path,
-        // renderSnapshot() so a burst of writes collapses into a single snapshot per frame.
+        // so a burst of writes collapses into one snapshot per frame) and tell the owning tab
-        renderVersion++;
+        // one of its panes changed.
-        RENDER_TICK.incrementAndGet();
+        contentVersion++;
+        onContentChange.run();
+    }
+
+    /** Paint the whole pane; see {@link TerminalRenderer#paintFull}. */
+    public void paintFull(GraphicsContext gc, boolean active) {
+        renderer.paintFull(gc, this, active);
+    }
+
+    /** Repaint what changed; see {@link TerminalRenderer#paintIncremental}. */
+    public void paintIncremental(GraphicsContext gc, boolean active) {
+        renderer.paintIncremental(gc, this, active);
     }
 
     @Override
     public void close() {
-        // Stop accepting reader-thread writes first, then shut the session (which unblocks
-        // and ends the reader), so terminal.close() can't race a write from that thread.
-        synchronized (terminal) {
-            closed = true;
-        }
         if (session != null) {
             session.close();
             session = null;
         }
         mouseEncoder.close();
-        synchronized (terminal) {
+        renderState.close();
         terminal.close();
     }
 }
-}

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

@@ -0,0 +1,60 @@
+package com.gregor.jprototerm;
+
+import javafx.scene.canvas.GraphicsContext;
+import javafx.scene.shape.ClosePath;
+import javafx.scene.shape.LineTo;
+import javafx.scene.shape.MoveTo;
+import javafx.scene.shape.Path;
+import javafx.scene.shape.PathElement;
+import javafx.scene.shape.Shape;
+
+/**
+ * Draws a {@link RenderTarget} onto a JavaFX canvas. The {@link Compositor} owns positioning
+ * and z-order; a renderer only fills the target's rect, clipped to the target's {@link
+ * RenderTarget#clip() clip region} so a repaint can never bleed over a pane on top.
+ * Implementations can change the look entirely — {@link GhosttyTerminalRenderer} is the real
+ * terminal renderer; a debug renderer could outline pane bounds instead.
+ *
+ * <p>A renderer may hold per-target state (e.g. a decoded-image cache), so an instance belongs
+ * to a single {@link TerminalPane}.
+ */
+abstract class TerminalRenderer {
+    /** Paint the whole target into its rect, clipped to its clip region. */
+    abstract void paintFull(GraphicsContext gc, RenderTarget target, boolean active);
+
+    /** Repaint only what changed since the last frame, clipped to the target's clip region. */
+    abstract void paintIncremental(GraphicsContext gc, RenderTarget target, boolean active);
+
+    protected static void clipRect(GraphicsContext gc, double x, double y, double width, double height) {
+        gc.beginPath();
+        gc.rect(x, y, width, height);
+        gc.clip();
+    }
+
+    /**
+     * Clip to {@code region} if given (the pane's rect minus the panes covering it, computed by
+     * {@code Shape.subtract} at layout), otherwise to the plain rect. The region is a rectilinear
+     * path, so it replays onto the canvas as move/line/close segments.
+     */
+    protected static void clip(GraphicsContext gc, double x, double y, double width, double height, Shape region) {
+        if (region == null) {
+            clipRect(gc, x, y, width, height);
+            return;
+        }
+        var elements = ((Path) region).getElements();
+        gc.beginPath();
+        if (elements.isEmpty()) {
+            gc.rect(x, y, 0.0, 0.0); // fully covered: clip to nothing
+        }
+        for (PathElement element : elements) {
+            if (element instanceof MoveTo moveTo) {
+                gc.moveTo(moveTo.getX(), moveTo.getY());
+            } else if (element instanceof LineTo lineTo) {
+                gc.lineTo(lineTo.getX(), lineTo.getY());
+            } else if (element instanceof ClosePath) {
+                gc.closePath();
+            }
+        }
+        gc.clip();
+    }
+}

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

@@ -1,139 +0,0 @@
-package com.gregor.jprototerm;
-
-import java.util.ArrayList;
-import java.util.List;
-
-/**
- * Holds the tabs and renders only the current one. Pane operations delegate to the current
- * tab; tab operations switch which tab is current. A single render version bumps on any
- * change (intra-tab or tab switch) so the renderer recomposites when needed.
- */
-public final class TerminalWorkspace implements AutoCloseable {
-    private final AppConfig config;
-    private final List<Tab> tabs = new ArrayList<>();
-    private int currentTab;
-    private long version;
-
-    public TerminalWorkspace(AppConfig config) {
-        this.config = config;
-        tabs.add(new Tab(config));
-    }
-
-    private Tab current() {
-        return tabs.get(currentTab);
-    }
-
-    public long version() {
-        return version;
-    }
-
-    public boolean isEmpty() {
-        return tabs.isEmpty();
-    }
-
-    public TerminalPane activePane() {
-        return current().activePane();
-    }
-
-    public List<TerminalPane> panes() {
-        return tabs.isEmpty() ? List.of() : current().panes();
-    }
-
-    public boolean isActive(TerminalPane pane) {
-        return !tabs.isEmpty() && current().isActive(pane);
-    }
-
-    public void layout(double width, double height, double topInset) {
-        if (!tabs.isEmpty()) {
-            current().layout(width, height, topInset);
-        }
-    }
-
-    public int tabCount() {
-        return tabs.size();
-    }
-
-    public int currentTabIndex() {
-        return currentTab;
-    }
-
-    public void focus(TerminalPane pane) {
-        if (!tabs.isEmpty() && current().focus(pane)) {
-            version++;
-        }
-    }
-
-    public void navigate(Direction direction) {
-        if (!tabs.isEmpty() && current().navigate(direction)) {
-            version++;
-        }
-    }
-
-    public void toggleFloating() {
-        if (tabs.isEmpty()) {
-            return;
-        }
-        current().toggleFloating();
-        version++;
-    }
-
-    public void createPane() {
-        if (tabs.isEmpty()) {
-            return;
-        }
-        current().createPane();
-        version++;
-    }
-
-    public void nextFloatingPane() {
-        if (tabs.isEmpty()) {
-            return;
-        }
-        current().nextFloatingPane();
-        version++;
-    }
-
-    public void closeActivePane() {
-        if (tabs.isEmpty()) {
-            return;
-        }
-        current().closeActivePane();
-        if (current().isEmpty()) {
-            // Closing a tab's last pane closes the tab. When no tabs remain the workspace
-            // is empty and Main quits.
-            tabs.remove(currentTab);
-            if (currentTab >= tabs.size()) {
-                currentTab = Math.max(0, tabs.size() - 1);
-            }
-        }
-        version++;
-    }
-
-    public void newTab() {
-        tabs.add(new Tab(config));
-        currentTab = tabs.size() - 1;
-        version++;
-    }
-
-    public void nextTab() {
-        if (tabs.size() > 1) {
-            currentTab = (currentTab + 1) % tabs.size();
-            version++;
-        }
-    }
-
-    public void previousTab() {
-        if (tabs.size() > 1) {
-            currentTab = (currentTab - 1 + tabs.size()) % tabs.size();
-            version++;
-        }
-    }
-
-    @Override
-    public void close() {
-        for (Tab tab : tabs) {
-            tab.close();
-        }
-        tabs.clear();
-    }
-}