From 8fafd3caddc5aad11df2e3547822632f29313156 Mon Sep 17 00:00:00 2001
From: Alois Zoitl <alois.zoitl@gmx.at>
Date: Wed, 10 Apr 2024 15:52:41 +0200
Subject: [PATCH] Scroll redraw on Windows lead to drawing artifacts

The reworked scrolling of the FigureCanvas didn't correctly calculated
the exposure areas which need to be redrawn after scrolling. This led to
drawing artifacts.
---
 .../src/org/eclipse/draw2d/FigureCanvas.java  | 36 +++++++++++++------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/org.eclipse.draw2d/src/org/eclipse/draw2d/FigureCanvas.java b/org.eclipse.draw2d/src/org/eclipse/draw2d/FigureCanvas.java
index f8a03b373..6d4e51ca8 100644
--- a/org.eclipse.draw2d/src/org/eclipse/draw2d/FigureCanvas.java
+++ b/org.eclipse.draw2d/src/org/eclipse/draw2d/FigureCanvas.java
@@ -411,24 +411,20 @@ private void performScroll(int hOffset, int vOffset) {
 		int dy = -vOffset + getViewport().getViewLocation().y;
 		Rectangle clientArea = getViewport().getBounds().getShrinked(getViewport().getInsets());
 		Rectangle blit = clientArea.getResized(-Math.abs(dx), -Math.abs(dy));
-		Rectangle expose = clientArea.getCopy();
 		Point dest = clientArea.getTopLeft();
 
-		expose.width = Math.abs(dx);
+		blit.width = Math.max(blit.width, 0);
+		blit.height = Math.max(blit.height, 0);
+
 		if (dx < 0) { // Moving left?
 			blit.translate(-dx, 0); // Move blit area to the right
-			expose.x = dest.x + blit.width;
-		} else {
-			// Moving right
+		} else { // Moving right
 			dest.x += dx; // Move expose area to the right
 		}
 
-		expose.height = Math.abs(dy);
 		if (dy < 0) { // Moving up?
 			blit.translate(0, -dy); // Move blit area down
-			expose.y = dest.y + blit.height; // Move expose area down
-		} else {
-			// Moving down
+		} else { // Moving down
 			dest.y += dy;
 		}
 
@@ -438,7 +434,7 @@ private void performScroll(int hOffset, int vOffset) {
 		getViewport().setHorizontalLocation(hOffset);
 		getViewport().setVerticalLocation(vOffset);
 		getViewport().setIgnoreScroll(false);
-		redraw(expose.x, expose.y, expose.width, expose.height, true);
+		scrollRedraw(dx, dy, clientArea, blit);
 	}
 
 	private void scrollChildren(int dx, int dy, Rectangle blit, Point dest) {
@@ -462,6 +458,26 @@ private void scrollChildren(int dx, int dy, Rectangle blit, Point dest) {
 		}
 	}
 
+	private void scrollRedraw(int dx, int dy, Rectangle clientArea, Rectangle blit) {
+		Rectangle expose = clientArea.getCopy();
+		if (dx != 0) {
+			expose.width = Math.abs(dx);
+			if (dx < 0) { // Moving left?
+				expose.x += blit.width; // Move expose area right
+			}
+			redraw(expose.x, expose.y, expose.width, expose.height, true);
+		}
+		if (dy != 0) {
+			expose.x = clientArea.x;
+			expose.width = clientArea.width;
+			expose.height = Math.abs(dy);
+			if (dy < 0) { // Moving up?
+				expose.y += blit.height; // Move expose area down
+			}
+			redraw(expose.x, expose.y, expose.width, expose.height, true);
+		}
+	}
+
 	/**
 	 * Sets the given border on the LightweightSystem's root figure.
 	 *