From 38822d66b8736dc120548671c02d3fa99eaab5b2 Mon Sep 17 00:00:00 2001
From: Gregor Lohaus <gregor.lohaus@8mylez.com>
Date: Sun, 31 May 2026 17:51:53 +0200
Subject: [PATCH] Fixed the partial-dirty blanking regression

---
 .../jprototerm/GhosttyTerminalRenderer.java   | 52 ++++++++++++++++---
 1 file changed, 46 insertions(+), 6 deletions(-)

diff --git a/src/main/java/com/gregor/jprototerm/GhosttyTerminalRenderer.java b/src/main/java/com/gregor/jprototerm/GhosttyTerminalRenderer.java
index 088dc47..f84709a 100644
--- a/src/main/java/com/gregor/jprototerm/GhosttyTerminalRenderer.java
+++ b/src/main/java/com/gregor/jprototerm/GhosttyTerminalRenderer.java
@@ -679,18 +679,21 @@ final class GhosttyTerminalRenderer extends TerminalRenderer {
         private PixelBuffer<IntBuffer> pixelBuffer;
         private WritableImage image;
         private long[] rowHashes = new long[0];
+        private boolean[] paintedRows = new boolean[0];
         private CursorState lastCursor = CursorState.none();
         private GlyphCache glyphs;
         private boolean valid;
 
         private void invalidate() {
             rowHashes = new long[0];
+            paintedRows = new boolean[0];
             lastCursor = CursorState.none();
             valid = false;
         }
 
         private boolean canPaintDirty(RenderStateSnapshot snapshot) {
-            return valid && snapshot != null && rowHashes.length == snapshot.rows();
+            return valid && snapshot != null && rowHashes.length == snapshot.rows()
+                    && paintedRows.length == snapshot.rows() && allRowsPainted();
         }
 
         private void paintFull(GraphicsContext gc, RenderStateSnapshot snapshot,
@@ -698,10 +701,11 @@ final class GhosttyTerminalRenderer extends TerminalRenderer {
             ensure(paneWidth, paneHeight);
             fillRect(0, 0, width, height, argbPre(PANE_BACKGROUND));
             if (snapshot != null) {
+                prepareRows(snapshot.rows());
                 paintSnapshot(snapshot);
                 drawCursor(snapshot);
                 rememberSnapshot(snapshot);
-                valid = true;
+                valid = allRowsPainted();
             } else {
                 invalidate();
             }
@@ -722,6 +726,7 @@ final class GhosttyTerminalRenderer extends TerminalRenderer {
             if (scroll != 0) {
                 scrollContentPixels(scroll);
                 scrollHashes(scroll);
+                scrollPaintedRows(scroll);
             }
 
             CursorState cursor = CursorState.from(snapshot);
@@ -739,7 +744,7 @@ final class GhosttyTerminalRenderer extends TerminalRenderer {
                 }
             }
             lastCursor = cursor;
-            valid = true;
+            valid = allRowsPainted();
             drawCursor(snapshot);
             drawBorder(active);
             present(gc, px, py);
@@ -771,7 +776,7 @@ final class GhosttyTerminalRenderer extends TerminalRenderer {
             }
             repaintCursorRow(snapshot, newCursorRow, repainted);
             lastCursor = cursor;
-            valid = true;
+            valid = allRowsPainted();
             drawCursor(snapshot);
             drawBorder(active);
             present(gc, px, py);
@@ -831,12 +836,12 @@ final class GhosttyTerminalRenderer extends TerminalRenderer {
         }
 
         private boolean canDiff(RenderStateSnapshot snapshot) {
-            return rowHashes.length == snapshot.rows() && snapshot.renderRows().size() == snapshot.rows();
+            return canPaintDirty(snapshot) && snapshot.renderRows().size() == snapshot.rows();
         }
 
         private void rememberSnapshot(RenderStateSnapshot snapshot) {
             if (rowHashes.length != snapshot.rows()) {
-                rowHashes = new long[snapshot.rows()];
+                prepareRows(snapshot.rows());
             }
             for (RenderRow row : snapshot.renderRows()) {
                 rowHashes[row.row()] = rowHash(row);
@@ -900,6 +905,17 @@ final class GhosttyTerminalRenderer extends TerminalRenderer {
             rowHashes = shifted;
         }
 
+        private void scrollPaintedRows(int rows) {
+            boolean[] shifted = new boolean[paintedRows.length];
+            for (int row = 0; row < shifted.length; row++) {
+                int previous = row - rows;
+                if (previous >= 0 && previous < paintedRows.length) {
+                    shifted[row] = paintedRows[previous];
+                }
+            }
+            paintedRows = shifted;
+        }
+
         private void scrollContentPixels(int rows) {
             int dy = rows * lineHeight();
             int top = contentTop();
@@ -956,6 +972,30 @@ final class GhosttyTerminalRenderer extends TerminalRenderer {
             paintRowSidePadding(row, rowTop, rowHeight);
             paintRowBackgrounds(row, rowTop, rowHeight);
             paintRowText(row, rowTop);
+            markPainted(row.row());
+        }
+
+        private void prepareRows(int rows) {
+            rowHashes = new long[rows];
+            paintedRows = new boolean[rows];
+        }
+
+        private void markPainted(int row) {
+            if (row >= 0 && row < paintedRows.length) {
+                paintedRows[row] = true;
+            }
+        }
+
+        private boolean allRowsPainted() {
+            if (paintedRows.length == 0) {
+                return false;
+            }
+            for (boolean painted : paintedRows) {
+                if (!painted) {
+                    return false;
+                }
+            }
+            return true;
         }
 
         private void paintRowSidePadding(RenderRow row, int rowTop, int rowHeight) {