[win32] Dynamic handle creation for region

This commit refactors Region in the win32 implementation to better
support multiple handles for different zoom settings by creating all
handles only on demand.

Author: akoch-yatta

bundles/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/graphics/RegionWin32Tests.java

@@ -57,7 +57,6 @@ public void testRegionMustBeScaledOnHandleOfScaledZoomLevel() {
 		assertEquals("scaled region's y position should be double of unscaled region", bounds.y * scalingFactor, scaledBounds.y);
 	}
 
-
 	@Test
 	public void testRegionMustIntersectProperlyOn175Zoom() {
 		Display display = Display.getDefault();
@@ -81,7 +80,24 @@ public void testRegionMustIntersectProperlyOn175Zoom() {
 		// be rounded independently
 		boolean shouldNotIntersect = region.intersects(0, 27, 100, 31);
 		assertFalse(shouldNotIntersect);
-
+		region.dispose();
 	}
 
+	@Test
+	public void testCreateRegionHandleWithDisposedRegionInvolved() {
+		Display display = Display.getDefault();
+
+		Region region = new Region(display);
+		region.add(0, 0, 100, 100);
+
+		Region region2 = new Region(display);
+		region.add(50, 50, 100, 100);
+
+		region.add(region2);
+
+		region2.dispose();
+		Region.win32_getHandle(region, 100);
+		Region.win32_getHandle(region, 200);
+		region.dispose();
+	}
 }

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

@@ -15,6 +15,7 @@
 
 
 import java.util.*;
+import java.util.function.*;
 import java.util.stream.*;
 
 import org.eclipse.swt.*;
@@ -452,8 +453,8 @@ public boolean isEmpty () {
 	if (isDisposed()) SWT.error(SWT.ERROR_GRAPHIC_DISPOSED);
 	RECT rect = new RECT ();
 	int result = OS.GetRgnBox (getHandleForInitialZoom(), rect);
-	if (result == OS.NULLREGION) return true;
-	return ((rect.right - rect.left) <= 0) || ((rect.bottom - rect.top) <= 0);
+		if (result == OS.NULLREGION) return true;
+		return ((rect.right - rect.left) <= 0) || ((rect.bottom - rect.top) <= 0);
 }
 
 /**
@@ -600,6 +601,32 @@ private void storeAndApplyOperationForAllHandles(Operation operation) {
 	zoomToHandle.forEach((zoom, handle) -> operation.apply(handle, zoom));
 }
 
+private <T> T applyUsingAnyMatchingHandle(int zoom, Function<Long, T> function) {
+	if (zoomToHandle.containsKey(zoom)) {
+		return function.apply(zoomToHandle.get(zoom));
+	} else {
+		return applyUsingTemporaryHandle(zoom, function);
+	}
+}
+
+private <T> T applyUsingTemporaryHandle(int zoom, Function<Long, T> function) {
+	long temporaryHandle = newRegionHandle(zoom);
+	try {
+		return function.apply(temporaryHandle);
+	} finally {
+		OS.DeleteObject(temporaryHandle);
+	}
+}
+
+private long newRegionHandle(int zoom) {
+	long newHandle = OS.CreateRectRgn (0, 0, 0, 0);
+	if (newHandle == 0) SWT.error(SWT.ERROR_NO_HANDLES);
+	for (Operation operation : operations) {
+		operation.apply(newHandle, zoom);
+	}
+	return newHandle;
+}
+
 /**
  * <b>IMPORTANT:</b> This method is not part of the public
  * API for Image. It is marked public only so that it
@@ -805,8 +832,7 @@ void translate(long handle, int zoom) {
 }
 
 private class OperationWithRegion extends Operation {
-
-	Region data;
+	private final Region data;
 
 	OperationWithRegion(OperationStrategy operationStrategy, Region data) {
 		super(operationStrategy);
@@ -815,30 +841,28 @@ private class OperationWithRegion extends Operation {
 
 	@Override
 	void add(long handle, int zoom) {
-		long scaledHandle = getHandleForScaledRegion(zoom);
-		OS.CombineRgn (handle, handle, scaledHandle, OS.RGN_OR);
+		data.applyUsingAnyMatchingHandle(zoom, regionHandle -> {
+			return OS.CombineRgn (handle, handle, regionHandle, OS.RGN_OR);
+		});
 	}
 
 	@Override
 	void subtract(long handle, int zoom) {
-		long scaledHandle = getHandleForScaledRegion(zoom);
-		OS.CombineRgn (handle, handle, scaledHandle, OS.RGN_DIFF);
+		data.applyUsingAnyMatchingHandle(zoom, regionHandle -> {
+			return OS.CombineRgn (handle, handle, regionHandle, OS.RGN_DIFF);
+		});
 	}
 
 	@Override
 	void intersect(long handle, int zoom) {
-		long scaledHandle = getHandleForScaledRegion(zoom);
-		OS.CombineRgn (handle, handle, scaledHandle, OS.RGN_AND);
+		data.applyUsingAnyMatchingHandle(zoom, regionHandle -> {
+			return OS.CombineRgn (handle, handle, regionHandle, OS.RGN_AND);
+		});
 	}
 
 	@Override
 	void translate(long handle, int zoom) {
 		throw new UnsupportedOperationException();
 	}
-
-	private long getHandleForScaledRegion(int zoom) {
-		if (data.isDisposed() || data == Region.this) SWT.error(SWT.ERROR_INVALID_ARGUMENT);
-		return win32_getHandle(data, zoom);
-	}
 }
 }