Adapt double buffering use cases for multi-zoom

This commit replaces three use cases where GC together with Images where
used to draw double buffered images. With new multi-zoom-setting in
Windows this leads to desctructive scaling and fragments caused by the
double buffering of Images/GCs created with different zoom. The changes
utilize the newly added ImageGcDrawer to provide a dynamic callback to
draw on a correctly initialized GC on demand.

Author: akoch-yatta

bundles/org.eclipse.jface.text/src/org/eclipse/jface/text/source/AnnotationRulerColumn.java

@@ -266,6 +266,13 @@ public Control createControl(CompositeRuler parentRuler, Composite parentControl
 			fCachedTextWidget= null;
 		});
 
+		fCanvas.addListener(SWT.ZoomChanged, e -> {
+			if (fBuffer != null) {
+				fBuffer.dispose();
+				fBuffer= null;
+			}
+		});
+
 		fMouseListener= new MouseListener() {
 			@Override
 			public void mouseUp(MouseEvent event) {
@@ -517,24 +524,28 @@ private void doubleBufferPaint(GC dest) {
 				fBuffer= null;
 			}
 		}
-		if (fBuffer == null)
-			fBuffer= new Image(fCanvas.getDisplay(), size.x, size.y);
+		if (fBuffer == null) {
+			fBuffer= new Image(fCanvas.getDisplay(), this::doPaint, size.x, size.y);
+		} else {
+			GC gc= new GC(fBuffer);
+			try {
+				doPaint(gc, size.x, size.y);
+			} finally {
+				gc.dispose();
+			}
+		}
+		dest.drawImage(fBuffer, 0, 0);
+	}
 
-		GC gc= new GC(fBuffer);
+	private void doPaint(GC gc, int width, int height) {
 		gc.setFont(fCachedTextWidget.getFont());
-		try {
-			gc.setBackground(fCanvas.getBackground());
-			gc.fillRectangle(0, 0, size.x, size.y);
-
-			if (fCachedTextViewer instanceof ITextViewerExtension5)
-				doPaint1(gc);
-			else
-				doPaint(gc);
-		} finally {
-			gc.dispose();
-		}
+		gc.setBackground(fCanvas.getBackground());
+		gc.fillRectangle(0, 0, width, height);
 
-		dest.drawImage(fBuffer, 0, 0);
+		if (fCachedTextViewer instanceof ITextViewerExtension5)
+			doPaint1(gc);
+		else
+			doPaint(gc);
 	}
 
 	/**

bundles/org.eclipse.jface.text/src/org/eclipse/jface/text/source/ChangeRulerColumn.java

@@ -199,6 +199,13 @@ public Control createControl(CompositeRuler parentRuler, Composite parentControl
 			fCachedTextWidget= null;
 		});
 
+		fCanvas.addListener(SWT.ZoomChanged, e -> {
+			if (fBuffer != null) {
+				fBuffer.dispose();
+				fBuffer= null;
+			}
+		});
+
 		fCanvas.addMouseListener(fMouseHandler);
 		fCanvas.addMouseMoveListener(fMouseHandler);
 
@@ -249,19 +256,15 @@ private void doubleBufferPaint(GC dest) {
 				fBuffer= null;
 			}
 		}
-		if (fBuffer == null)
-			fBuffer= new Image(fCanvas.getDisplay(), size.x, size.y);
-
-		GC gc= new GC(fBuffer);
-		gc.setFont(fCanvas.getFont());
-
-		try {
-			gc.setBackground(getBackground());
-			gc.fillRectangle(0, 0, size.x, size.y);
-
-			doPaint(gc);
-		} finally {
-			gc.dispose();
+		if (fBuffer == null) {
+			fBuffer= new Image(fCanvas.getDisplay(), this::doPaint, size.x, size.y);
+		} else {
+			GC gc= new GC(fBuffer);
+			try {
+				doPaint(gc, size.x, size.y);
+			} finally {
+				gc.dispose();
+			}
 		}
 
 		dest.drawImage(fBuffer, 0, 0);
@@ -291,6 +294,14 @@ protected final boolean isViewerCompletelyShown() {
 		return JFaceTextUtil.isShowingEntireContents(fCachedTextWidget);
 	}
 
+	private void doPaint(GC gc, int width, int height) {
+		gc.setFont(fCanvas.getFont());
+		gc.setBackground(getBackground());
+		gc.fillRectangle(0, 0, width, height);
+
+		doPaint(gc);
+	}
+
 	/**
 	 * Draws the ruler column.
 	 *

bundles/org.eclipse.jface.text/src/org/eclipse/jface/text/source/LineNumberRulerColumn.java

@@ -34,6 +34,7 @@
 import org.eclipse.swt.graphics.FontMetrics;
 import org.eclipse.swt.graphics.GC;
 import org.eclipse.swt.graphics.Image;
+import org.eclipse.swt.graphics.ImageGcDrawer;
 import org.eclipse.swt.graphics.Point;
 import org.eclipse.swt.graphics.Rectangle;
 import org.eclipse.swt.widgets.Canvas;
@@ -616,7 +617,13 @@ public void addMouseListener(MouseListener listener) {
 			fCachedTextWidget= null;
 		});
 
-		fCanvas.addListener(SWT.ZoomChanged, e -> computeIndentations());
+		fCanvas.addListener(SWT.ZoomChanged, e -> {
+			computeIndentations();
+			if (fBuffer != null) {
+				fBuffer.dispose();
+				fBuffer= null;
+			}
+		});
 
 		fMouseHandler= new MouseHandler();
 		fCanvas.addMouseListener(fMouseHandler);
@@ -679,10 +686,28 @@ private void doubleBufferPaint(GC dest) {
 			return;
 		}
 
-		boolean bufferStillValid = fBuffer != null;
 		if (fBuffer == null) {
-			fBuffer= new Image(fCanvas.getDisplay(), size.x, size.y);
+			fBuffer= newFullBufferImage(size);
+		} else {
+			doPaint(visibleLines, size);
 		}
+		dest.drawImage(fBuffer, 0, 0);
+	}
+
+	private Image newFullBufferImage(Point size) {
+		ImageGcDrawer imageGcDrawer= (gc, imageWidth, imageHeight) -> {
+			ILineRange lines= JFaceTextUtil.getVisibleModelLines(fCachedTextViewer);
+			if (lines == null) {
+				return;
+			}
+			// We redraw everything; paint directly into the buffer
+			initializeGC(gc, 0, 0, imageWidth, imageHeight);
+			doPaint(gc, lines);
+		};
+		return new Image(fCanvas.getDisplay(), imageGcDrawer, size.x, size.y);
+	}
+
+	private void doPaint(ILineRange visibleLines, Point size) {
 		GC bufferGC= new GC(fBuffer);
 		Image newBuffer= null;
 		try {
@@ -696,7 +721,7 @@ private void doubleBufferPaint(GC dest) {
 			int bottomWidgetLine= JFaceTextUtil.modelLineToWidgetLine(fCachedTextViewer, bottomModelLine);
 			boolean atEnd= bottomWidgetLine + 1 >= fCachedTextWidget.getLineCount();
 			int height= size.y;
-			if (dy != 0 && !atEnd && bufferStillValid && fLastTopPixel >= 0 && numberOfLines > 1 && numberOfLines == fLastNumberOfLines) {
+			if (dy != 0 && !atEnd && fLastTopPixel >= 0 && numberOfLines > 1 && numberOfLines == fLastNumberOfLines) {
 				int bottomPixel= fCachedTextWidget.getLinePixel(bottomWidgetLine + 1);
 				if (dy > 0 && bottomPixel < size.y) {
 					// Can occur on GTK with static scrollbars; see bug 551320.
@@ -745,16 +770,7 @@ private void doubleBufferPaint(GC dest) {
 			fLastBottomModelLine= bottomModelLine;
 			fLastHeight= height;
 			if (dy != 0) {
-				// Some rulers may paint outside the line region. Let them paint in a new image,
-				// the copy the wanted bits.
-				newBuffer= new Image(fCanvas.getDisplay(), size.x, size.y);
-				GC localGC= new GC(newBuffer);
-				try {
-					initializeGC(localGC, 0, bufferY, size.x, bufferH);
-					doPaint(localGC, visibleLines);
-				} finally {
-					localGC.dispose();
-				}
+				newBuffer= newBufferImage(size, bufferY, bufferH, visibleLines);
 				bufferGC.drawImage(newBuffer, 0, bufferY, size.x, bufferH, 0, bufferY, size.x, bufferH);
 				if (dy > 0 && bufferY + bufferH < size.y) {
 					// Scrolled down in the text, but didn't use the full height of the Canvas: clear
@@ -774,7 +790,16 @@ private void doubleBufferPaint(GC dest) {
 				newBuffer.dispose();
 			}
 		}
-		dest.drawImage(fBuffer, 0, 0);
+	}
+
+	private Image newBufferImage(Point size, int bufferY, int bufferH, final ILineRange visibleLines) {
+		ImageGcDrawer imageGcDrawer= (localGC, imageWidth, imageHeight) -> {
+			// Some rulers may paint outside the line region. Let them paint in a new image,
+			// the copy the wanted bits.
+			initializeGC(localGC, 0, bufferY, imageWidth, bufferH);
+			doPaint(localGC, visibleLines);
+		};
+		return new Image(fCanvas.getDisplay(), imageGcDrawer, size.x, size.y);
 	}
 
 	private void initializeGC(GC gc, int x, int y, int width, int height) {

bundles/org.eclipse.jface.text/src/org/eclipse/jface/text/source/OverviewRuler.java

@@ -597,6 +597,13 @@ public void mouseEnter(MouseEvent e) {
 			fTextViewer= null;
 		});
 
+		fCanvas.addListener(SWT.ZoomChanged, e -> {
+			if (fBuffer != null) {
+				fBuffer.dispose();
+				fBuffer= null;
+			}
+		});
+
 		fCanvas.addMouseListener(new MouseAdapter() {
 			@Override
 			public void mouseDown(MouseEvent event) {
@@ -676,23 +683,27 @@ private void doubleBufferPaint(GC dest) {
 				fBuffer= null;
 			}
 		}
-		if (fBuffer == null)
-			fBuffer= new Image(fCanvas.getDisplay(), size.x, size.y);
-
-		GC gc= new GC(fBuffer);
-		try {
-			gc.setBackground(fCanvas.getBackground());
-			gc.fillRectangle(0, 0, size.x, size.y);
+		if (fBuffer == null) {
+			fBuffer= new Image(fCanvas.getDisplay(), this::doPaint, size.x, size.y);
+		} else {
+			GC gc= new GC(fBuffer);
+			try {
+				doPaint(gc, size.x, size.y);
+			} finally {
+				gc.dispose();
+			}
+		}
 
-			cacheAnnotations();
+		dest.drawImage(fBuffer, 0, 0);
+	}
 
-			doPaint(gc);
+	private void doPaint(GC gc, int width, int height) {
+		gc.setBackground(fCanvas.getBackground());
+		gc.fillRectangle(0, 0, width, height);
 
-		} finally {
-			gc.dispose();
-		}
+		cacheAnnotations();
 
-		dest.drawImage(fBuffer, 0, 0);
+		doPaint(gc);
 	}
 
 	private void cacheAnnotations() {

bundles/org.eclipse.jface.text/src/org/eclipse/jface/text/source/VerticalRuler.java

@@ -159,6 +159,13 @@ public Control createControl(Composite parent, ITextViewer textViewer) {
 			fTextViewer= null;
 		});
 
+		fCanvas.addListener(SWT.ZoomChanged, e -> {
+			if (fBuffer != null) {
+				fBuffer.dispose();
+				fBuffer= null;
+			}
+		});
+
 		fCanvas.addMouseListener(new MouseListener() {
 			@Override
 			public void mouseUp(MouseEvent event) {
@@ -223,27 +230,31 @@ private void doubleBufferPaint(GC dest) {
 				fBuffer= null;
 			}
 		}
-		if (fBuffer == null)
-			fBuffer= new Image(fCanvas.getDisplay(), size.x, size.y);
-
-		GC gc= new GC(fBuffer);
-		gc.setFont(fTextViewer.getTextWidget().getFont());
-		try {
-			gc.setBackground(fCanvas.getBackground());
-			gc.fillRectangle(0, 0, size.x, size.y);
-
-			if (fTextViewer instanceof ITextViewerExtension5)
-				doPaint1(gc);
-			else
-				doPaint(gc);
 
-		} finally {
-			gc.dispose();
+		if (fBuffer == null) {
+			fBuffer= new Image(fCanvas.getDisplay(), this::doPaint, size.x, size.y);
+		} else {
+			GC gc= new GC(fBuffer);
+			try {
+				doPaint(gc, size.x, size.y);
+			} finally {
+				gc.dispose();
+			}
 		}
-
 		dest.drawImage(fBuffer, 0, 0);
 	}
 
+	private void doPaint(GC gc, int width, int height) {
+		gc.setFont(fTextViewer.getTextWidget().getFont());
+		gc.setBackground(fCanvas.getBackground());
+		gc.fillRectangle(0, 0, width, height);
+
+		if (fTextViewer instanceof ITextViewerExtension5)
+			doPaint1(gc);
+		else
+			doPaint(gc);
+	}
+
 	/**
 	 * Returns the document offset of the upper left corner of the
 	 * widgets view port, possibly including partially visible lines.