Make double buffering of Terminal adopt to higher monitor zooms

The terminal implementation uses a custom double buffering
implementation for rendering the current line. On most Platforms (Linux
and MacOS) the current implementation will always render the
double-buffered image at 100% zoom, even if the target zoom is higher.

This change adapts the implementation to directly render into the actual
control and enable native double buffering for the control instead. This
ensures that the contents are rendered at the actual target zoom,
producing sharper results on HiDPI monitors when using MacOS or Linux.

Fixes #2295

Fixes #2191

Author: HeikoKlare

terminal/bundles/org.eclipse.terminal.control/src/org/eclipse/terminal/internal/textcanvas/TextCanvas.java

@@ -101,7 +101,7 @@ private enum SelectionMode {
 	 * (SWT.H_SCROLL and SWT.V_SCROLL are automatically added).
 	 */
 	public TextCanvas(Composite parent, ITextCanvasModel model, int style, ILinelRenderer cellRenderer) {
-		super(parent, style | SWT.H_SCROLL | SWT.V_SCROLL);
+		super(parent, style | SWT.H_SCROLL | SWT.V_SCROLL | SWT.DOUBLE_BUFFERED);
 		fCellRenderer = cellRenderer;
 		setCellWidth(fCellRenderer.getCellWidth());
 		setCellHeight(fCellRenderer.getCellHeight());

terminal/bundles/org.eclipse.terminal.control/src/org/eclipse/terminal/internal/textcanvas/TextLineRenderer.java

@@ -22,7 +22,6 @@
 import org.eclipse.swt.graphics.Color;
 import org.eclipse.swt.graphics.Font;
 import org.eclipse.swt.graphics.GC;
-import org.eclipse.swt.graphics.Image;
 import org.eclipse.swt.graphics.Point;
 import org.eclipse.swt.graphics.RGB;
 import org.eclipse.terminal.connector.Logger;
@@ -57,27 +56,25 @@ public int getCellHeight() {
 
 	@Override
 	public void drawLine(ITextCanvasModel model, GC gc, int line, int x, int y, int colFirst, int colLast) {
+		gc.setAntialias(SWT.ON);
 		int width = getCellWidth() * (colLast - colFirst);
 		int height = getCellHeight();
 		if (width <= 0 || height <= 0) {
 			return;
 		}
-		Image buffer = new Image(gc.getDevice(), width, height);
-		GC doubleBufferGC = new GC(buffer);
-		doubleBufferGC.setAntialias(SWT.ON);
 		if (line < 0 || line >= getTerminalText().getHeight() || colFirst >= getTerminalText().getWidth()
 				|| colFirst - colLast == 0) {
-			fillBackground(doubleBufferGC, 0, 0, width, height);
+			fillBackground(gc, x, y, width, height);
 		} else {
 			colLast = Math.min(colLast, getTerminalText().getWidth());
 			LineSegment[] segments = getTerminalText().getLineSegments(line, colFirst, colLast - colFirst);
 			for (int i = 0; i < segments.length; i++) {
 				LineSegment segment = segments[i];
 				TerminalStyle style = segment.getStyle();
-				setupGC(doubleBufferGC, style);
+				setupGC(gc, style);
 				String text = segment.getText();
-				drawText(doubleBufferGC, 0, 0, colFirst, segment.getColumn(), text);
-				drawCursor(model, doubleBufferGC, line, 0, 0, colFirst);
+				drawText(gc, x, y, colFirst, segment.getColumn(), text);
+				drawCursor(model, gc, line, x, y, colFirst);
 			}
 			if (fModel.hasHoverSelection(line)) {
 				if (DEBUG_HOVER) {
@@ -89,14 +86,14 @@ public void drawLine(ITextCanvasModel model, GC gc, int line, int x, int y, int
 				int colEnd = line == hsEnd.y ? hsEnd.x : getTerminalText().getWidth();
 				if (colStart < colEnd) {
 					RGB defaultFg = fStyleMap.getForegrondRGB(null);
-					doubleBufferGC.setForeground(new Color(doubleBufferGC.getDevice(), defaultFg));
-					drawUnderline(doubleBufferGC, colStart, colEnd);
+					gc.setForeground(new Color(gc.getDevice(), defaultFg));
+					drawUnderline(gc, x, y, colStart, colEnd);
 				}
 			}
 			if (fModel.hasLineSelection(line)) {
 				TerminalStyle style = TerminalStyle.getStyle(TerminalColor.SELECTION_FOREGROUND,
 						TerminalColor.SELECTION_BACKGROUND);
-				setupGC(doubleBufferGC, style);
+				setupGC(gc, style);
 				Point start = model.getSelectionStart();
 				Point end = model.getSelectionEnd();
 				char[] chars = model.getTerminalText().getChars(line);
@@ -115,14 +112,11 @@ public void drawLine(ITextCanvasModel model, GC gc, int line, int x, int y, int
 					len = Math.min(len, chars.length - offset);
 					if (len > 0) {
 						String text = new String(chars, offset, len);
-						drawText(doubleBufferGC, 0, 0, colFirst, offset, text);
+						drawText(gc, x, y, colFirst, offset, text);
 					}
 				}
 			}
 		}
-		gc.drawImage(buffer, x, y);
-		doubleBufferGC.dispose();
-		buffer.dispose();
 	}
 
 	private void fillBackground(GC gc, int x, int y, int width, int height) {
@@ -188,9 +182,9 @@ private void drawText(GC gc, int x, int y, int colFirst, int col, String text) {
 	 * @param colStart Starting text column to underline (inclusive)
 	 * @param colEnd Ending text column to underline (inclusive)
 	 */
-	private void drawUnderline(GC gc, int colStart, int colEnd) {
-		int y = getCellHeight() - 1;
-		int x = getCellWidth() * colStart;
+	private void drawUnderline(GC gc, int xOffset, int yOffset, int colStart, int colEnd) {
+		int y = yOffset + getCellHeight() - 1;
+		int x = xOffset + getCellWidth() * colStart;
 
 		// x2 is the right side of last column being underlined.
 		int x2 = (colEnd + 1) * getCellWidth() - 1;