introduce GC.create which returns an AutoCloseable

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/AnimatedProgress.java

@@ -195,7 +195,9 @@ public synchronized void start() {
 	final Runnable [] timer = new Runnable [1];
 	timer [0] = () -> {
 		if (!active) return;
-		GC.drawOn(AnimatedProgress.this, gc -> paintStripes(gc));
+		try(var gc = GC.create(AnimatedProgress.this)) {
+			paintStripes(gc);
+		}
 		display.timerExec (SLEEP, timer [0]);
 	};
 	display.timerExec (SLEEP, timer [0]);

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/CLabel.java

@@ -270,7 +270,7 @@ private Point getTotalSize(Image image, String text) {
 		size.y += r.height;
 	}
 
-	GC.drawOn(this, gc -> {
+	try(var gc = GC.create(this)) {
 		if (text != null && text.length() > 0) {
 			Point e = gc.textExtent(text, DRAW_FLAGS);
 			size.x += e.x;
@@ -279,7 +279,7 @@ private Point getTotalSize(Image image, String text) {
 		} else {
 			size.y = Math.max(size.y, gc.getFontMetrics().getHeight());
 		}
-	});
+	}
 
 	return size;
 }

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/CTabFolder.java

@@ -3835,8 +3835,8 @@ boolean updateItems() {
 }
 
 boolean updateItems (int showIndex) {
-	final boolean changed[] = new boolean[] {false};
-	GC.drawOn(this, gc -> {
+	boolean changed = false;
+	try(var gc = GC.create(this)) {
 		if (!single && !mru && showIndex != -1) {
 			// make sure selected item will be showing
 			int firstIndex = showIndex;
@@ -3899,31 +3899,31 @@ boolean updateItems (int showIndex) {
 		}
 
 		boolean oldShowChevron = showChevron;
-		changed[0] = setItemSize(gc);
+		changed = setItemSize(gc);
 		updateButtons();
 		boolean chevronChanged = showChevron != oldShowChevron;
 		if (chevronChanged) {
 			if (updateTabHeight(false)) {
 				// Tab height has changed. Item sizes have to be set again.
-				changed[0] |= setItemSize(gc);
+				changed |= setItemSize(gc);
 			}
 		}
-		changed[0] |= setItemLocation(gc);
+		changed |= setItemLocation(gc);
 		setButtonBounds();
-		changed[0] |= chevronChanged;
-		if (changed[0] && getToolTipText() != null) {
+		changed |= chevronChanged;
+		if (changed && getToolTipText() != null) {
 			Point pt = getDisplay().getCursorLocation();
 			pt = toControl(pt);
 			_setToolTipText(pt.x, pt.y);
 		}
-	});
-	return changed[0];
+	}
+	return changed;
 }
 boolean updateTabHeight(boolean force){
 	int oldHeight = tabHeight;
-	GC.drawOn(this, gc ->{
+	try(var gc = GC.create(this)) {
 		tabHeight = renderer.computeSize(CTabFolderRenderer.PART_HEADER, SWT.NONE, gc, SWT.DEFAULT, SWT.DEFAULT).y;
-	});
+	}
 	if (fixedTabHeight == SWT.DEFAULT && controls != null && controls.length > 0) {
 		for (int i = 0; i < controls.length; i++) {
 			if ((controlAlignments[i] & SWT.WRAP) == 0 && !controls[i].isDisposed() && controls[i].getVisible()) {
@@ -4009,7 +4009,9 @@ void updateBkImages(boolean colorChanged) {
 							bkImageBounds[i] = bounds;
 							if (controlBkImages[i] != null) controlBkImages[i].dispose();
 							controlBkImages[i] = new Image(control.getDisplay(), bounds);
-							GC.drawOn(controlBkImages[i], gc-> renderer.draw(CTabFolderRenderer.PART_BACKGROUND, 0, bounds, gc));
+							try(var gc = GC.create(controlBkImages[i])) {
+								renderer.draw(CTabFolderRenderer.PART_BACKGROUND, 0, bounds, gc);
+							}
 							control.setBackground(null);
 							control.setBackgroundImage(controlBkImages[i]);
 						}

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/CTabFolderLayout.java

@@ -29,22 +29,21 @@ protected Point computeSize(Composite composite, int wHint, int hHint, boolean f
 	CTabItem[] items = folder.items;
 	CTabFolderRenderer renderer = folder.renderer;
 	// preferred width of tab area to show all tabs
-	final int[] tabW = new int[] {0};
-	final int[] selectedIndex = new int[] {folder.selectedIndex};
-	if (selectedIndex[0] == -1) selectedIndex[0] = 0;
-	final int[] wrapHeight = new int[] {0};
-	GC.drawOn(folder, gc -> {
+	int tabW = 0;
+	int selectedIndex = folder.selectedIndex;
+	if (selectedIndex == -1) selectedIndex = 0;
+	int width = 0, wrapHeight = 0;
+	try(var gc = GC.create(folder)) {
 		for (int i = 0; i < items.length; i++) {
 			if (folder.single) {
-				tabW[0] = Math.max(tabW[0], renderer.computeSize(i, SWT.SELECTED, gc, SWT.DEFAULT, SWT.DEFAULT).x);
+				tabW = Math.max(tabW, renderer.computeSize(i, SWT.SELECTED, gc, SWT.DEFAULT, SWT.DEFAULT).x);
 			} else {
 				int state = 0;
-				if (i == selectedIndex[0]) state |= SWT.SELECTED;
-				tabW[0] += renderer.computeSize(i, state, gc, SWT.DEFAULT, SWT.DEFAULT).x;
+				if (i == selectedIndex) state |= SWT.SELECTED;
+				tabW += renderer.computeSize(i, state, gc, SWT.DEFAULT, SWT.DEFAULT).x;
 			}
 		}
 
-		int width = 0;
 		boolean leftControl = false, rightControl = false;
 		if (wHint == SWT.DEFAULT) {
 			for (int i = 0; i < folder.controls.length; i++) {
@@ -67,7 +66,7 @@ protected Point computeSize(Composite composite, int wHint, int hHint, boolean f
 				if (positions[0][i]) {
 					minY = Math.min(minY, rects[i].y);
 					maxY = Math.max(maxY, rects[i].y + rects[i].height);
-					wrapHeight[0] = maxY - minY;
+					wrapHeight = maxY - minY;
 				} else {
 					if ((folder.controlAlignments[i] & SWT.LEAD) != 0) {
 						leftControl = true;
@@ -80,8 +79,8 @@ protected Point computeSize(Composite composite, int wHint, int hHint, boolean f
 		}
 		if (leftControl) width += CTabFolder.SPACING * 2;
 		if (rightControl) width += CTabFolder.SPACING * 2;
-		tabW[0] += width;
-	});
+		tabW += width;
+	}
 
 	int controlW = 0;
 	int controlH = 0;
@@ -95,8 +94,8 @@ protected Point computeSize(Composite composite, int wHint, int hHint, boolean f
 		}
 	}
 
-	int minWidth = Math.max(tabW[0], controlW + folder.marginWidth);
-	int minHeight = (folder.minimized) ? 0 : controlH + wrapHeight[0];
+	int minWidth = Math.max(tabW, controlW + folder.marginWidth);
+	int minHeight = (folder.minimized) ? 0 : controlH + wrapHeight;
 	if (minWidth == 0) minWidth = CTabFolder.DEFAULT_WIDTH;
 	if (minHeight == 0) minHeight = CTabFolder.DEFAULT_HEIGHT;
 

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/StyledTextDropTargetEffect.java

@@ -161,8 +161,9 @@ public void dragOver(DropTargetEvent event) {
 					 pt.y >= scrollY && pt.y <= (scrollY + SCROLL_TOLERANCE))) {
 					if (System.currentTimeMillis() >= scrollBeginTime) {
 						Rectangle area = text.getClientArea();
-						GC.drawOn(text, gc->{
+						try(var gc = GC.create(text)) {
 							FontMetrics fm = gc.getFontMetrics();
+
 							double charWidth = fm.getAverageCharacterWidth();
 							int scrollAmount = (int) (10*charWidth);
 							if (pt.x < area.x + 3*charWidth) {
@@ -173,18 +174,18 @@ public void dragOver(DropTargetEvent event) {
 								int leftPixel = text.getHorizontalPixel();
 								text.setHorizontalPixel(leftPixel + scrollAmount);
 							}
-						});
-						int lineHeight = text.getLineHeight();
-						if (pt.y < area.y + lineHeight) {
-							int topPixel = text.getTopPixel();
-							text.setTopPixel(topPixel - lineHeight);
-						}
-						if (pt.y > area.height - lineHeight) {
-							int topPixel = text.getTopPixel();
-							text.setTopPixel(topPixel + lineHeight);
+							int lineHeight = text.getLineHeight();
+							if (pt.y < area.y + lineHeight) {
+								int topPixel = text.getTopPixel();
+								text.setTopPixel(topPixel - lineHeight);
+							}
+							if (pt.y > area.height - lineHeight) {
+								int topPixel = text.getTopPixel();
+								text.setTopPixel(topPixel + lineHeight);
+							}
+							scrollBeginTime = 0;
+							scrollX = scrollY = -1;
 						}
-						scrollBeginTime = 0;
-						scrollX = scrollY = -1;
 					}
 				} else {
 					scrollBeginTime = System.currentTimeMillis() + SCROLL_HYSTERESIS;

bundles/org.eclipse.swt/Eclipse SWT Custom Widgets/common/org/eclipse/swt/custom/StyledTextRenderer.java

@@ -1500,10 +1500,10 @@ void setFont(Font font, int tabs) {
 	tabWidth = layout.getBounds().width;
 	layout.dispose();
 	if (styledText != null) {
-		GC.drawOn(styledText, gc->{
+		try(var gc = GC.create(styledText)) {
 			averageCharWidth = (int) gc.getFontMetrics().getAverageCharacterWidth();
 			fixedPitch = gc.stringExtent("l").x == gc.stringExtent("W").x; //$NON-NLS-1$ //$NON-NLS-2$
-		});
+		}
 	}
 }
 void setLineAlignment(int startLine, int count, int alignment) {

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/GC.java

@@ -59,7 +59,21 @@
  * @see <a href="http://www.eclipse.org/swt/examples.php">SWT Examples: GraphicsExample, PaintExample</a>
  * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
  */
-public final class GC extends Resource {
+public sealed class GC extends Resource permits GC.Closeable {
+
+	public static final class Closeable extends GC implements AutoCloseable {
+		Closeable(Drawable drawable, int style) {
+			super(drawable, style);
+		}
+		@Override
+		public void close() {
+			dispose();
+		}
+	}
+
+	public static GC.Closeable create(Drawable drawable) {
+		return new Closeable(drawable, SWT.NONE);
+	}
 
 	/**
 	 * the handle to the OS device context
@@ -114,8 +128,7 @@ public final class GC extends Resource {
  * foreground color, background color and font in the GC
  * to match those in the drawable.
  * <p>
- * You must dispose the graphics context when it is no longer required
- * or better use {@link #drawOn(Drawable, GCRunnable)} which takes care of disposing the GC.
+ * You must dispose the graphics context when it is no longer required.
  * </p>
  * @param drawable the drawable to draw on
  * @exception IllegalArgumentException <ul>
@@ -178,22 +191,6 @@ public GC(Drawable drawable, int style) {
 	init();
 }
 
-/**
- * creates a GC on the Drawable, calls run on the GCRunnable and disposes the GC in a finally block
- * @param <E>
- * @param drawable
- * @param runnable
- * @throws E
- */
-public static <E extends Exception> void drawOn(Drawable drawable, GCRunnable<E> runnable) throws E {
-	GC gc = new GC(drawable);
-	try {
-		runnable.run(gc);
-	} finally {
-		gc.dispose();
-	}
-}
-
 static int checkStyle(int style) {
 	if ((style & SWT.LEFT_TO_RIGHT) != 0) style &= ~SWT.RIGHT_TO_LEFT;
 	return style & (SWT.LEFT_TO_RIGHT | SWT.RIGHT_TO_LEFT);