Destroy unused handles of resources

This Contribution destroys those handles for the resources which were
created for zoom levels which no monitor has anymore. The process is
triggered on a DPI_CHANGED event.

contributes to #62 and eclipse-platform#127

bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/graphics/Resource.java

@@ -13,6 +13,7 @@
  *******************************************************************************/
 package org.eclipse.swt.graphics;
 
+import java.util.*;
 import java.util.function.*;
 
 import org.eclipse.swt.*;
@@ -123,6 +124,17 @@ public Resource() {
 void destroy() {
 }
 
+/**
+ * Destroy all handles of the resource which are not necessary for the given
+ * zoom levels. This method is supposed to be overridden by sub-classes that
+ * retain handles for different zoom levels.
+ *
+ * @param zoomLevels The zoom levels for which the handles are supposed to be
+ *                   retained.
+ */
+void destroyHandlesExcept(Set<Integer> zoomLevels) {
+}
+
 /**
  * Disposes of the operating system resources associated with
  * this resource. Applications must dispose of all resources

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

@@ -14,10 +14,14 @@
 package org.eclipse.swt.graphics;
 
 
+import java.util.*;
+import java.util.concurrent.*;
+
 import org.eclipse.swt.*;
 import org.eclipse.swt.internal.*;
 import org.eclipse.swt.internal.gdip.*;
 import org.eclipse.swt.internal.win32.*;
+import org.eclipse.swt.widgets.*;
 
 /**
  * This class is the abstract superclass of all device objects,
@@ -55,6 +59,7 @@ public abstract class Device implements Drawable {
 	String[] loadedFonts;
 
 	volatile boolean disposed;
+	private Set<Resource> resourcesWithZoomSupport  = ConcurrentHashMap.newKeySet();
 
 	/*
 	* TEMPORARY CODE. When a graphics object is
@@ -914,6 +919,8 @@ protected void release () {
 		Gdip.GdiplusShutdown (gdipToken[0]);
 	}
 	SWTFontProvider.disposeFontRegistry(this);
+	resourcesWithZoomSupport.clear();
+	resourcesWithZoomSupport = null;
 	gdipToken = null;
 	scripts = null;
 	logFonts = null;
@@ -947,4 +954,24 @@ public void setWarnings (boolean warnings) {
 protected int getDeviceZoom () {
 	return DPIUtil.mapDPIToZoom ( _getDPIx ());
 }
+
+void registerResourceWithZoomSupport(Resource resource) {
+	resourcesWithZoomSupport.add(resource);
+}
+
+/**
+ * Destroys the handles of all the resources in the resource tracker by
+ * identifying the zoom levels which is not valid for any monitor
+ *
+ * @noreference This method is not intended to be referenced by clients.
+ */
+public static void win32_destroyUnusedHandles(Display display) {
+	Set<Integer> availableZoomLevels = new HashSet<>();
+	for (Monitor monitor : display.getMonitors()) {
+	    availableZoomLevels.add(DPIUtil.getZoomForAutoscaleProperty(monitor.getZoom()));
+	}
+	for (Resource resource: ((Device) display).resourcesWithZoomSupport) {
+		resource.destroyHandlesExcept(availableZoomLevels);
+	}
+}
 }

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

@@ -164,6 +164,7 @@ public final class Image extends Resource implements Drawable {
 Image (Device device) {
 	super(device);
 	initialNativeZoom = DPIUtil.getNativeDeviceZoom();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -209,6 +210,7 @@ public Image(Device device, int width, int height) {
 	height = DPIUtil.scaleUp (height, zoom);
 	init(width, height);
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -311,6 +313,7 @@ public Image(Device device, Image srcImage, int flag) {
 			SWT.error(SWT.ERROR_INVALID_ARGUMENT);
 	}
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -355,6 +358,7 @@ public Image(Device device, Rectangle bounds) {
 	bounds = DPIUtil.scaleUp (bounds, getZoom());
 	init(bounds.width, bounds.height);
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -388,6 +392,7 @@ public Image(Device device, ImageData data) {
 	data = DPIUtil.autoScaleUp(device, this.dataAtBaseZoom);
 	init(data, getZoom());
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -434,6 +439,7 @@ public Image(Device device, ImageData source, ImageData mask) {
 	mask = ImageData.convertMask(mask);
 	init(this.device, this, source, mask, getZoom());
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -496,6 +502,7 @@ public Image (Device device, InputStream stream) {
 	ImageData data = DPIUtil.autoScaleUp(device, this.dataAtBaseZoom);
 	init(data, getZoom());
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -538,6 +545,7 @@ public Image (Device device, String filename) {
 	ImageData data = DPIUtil.autoScaleUp(device, this.dataAtBaseZoom);
 	init(data, getZoom());
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -586,6 +594,7 @@ public Image(Device device, ImageFileNameProvider imageFileNameProvider) {
 		init(resizedData, getZoom());
 	}
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -625,6 +634,7 @@ public Image(Device device, ImageDataProvider imageDataProvider) {
 	ImageData resizedData = DPIUtil.scaleImageData(device, data.element(), getZoom(), data.zoom());
 	init (resizedData, getZoom());
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 private ImageData adaptImageDataIfDisabledOrGray(ImageData data) {
@@ -1186,16 +1196,32 @@ void destroy () {
 
 private void destroyHandle () {
 	for (Long handle : zoomLevelToHandle.values()) {
-		if (type == SWT.ICON) {
-			OS.DestroyIcon (handle);
-		} else {
-			OS.DeleteObject (handle);
-		}
+		destroyHandle(handle);
 	}
 	zoomLevelToHandle.clear();
 	handle = 0;
 }
 
+@Override
+void destroyHandlesExcept(Set<Integer> zoomLevels) {
+	zoomLevelToHandle.entrySet().removeIf(entry -> {
+		final Integer zoom = entry.getKey();
+		if (!zoomLevels.contains(zoom) && zoom != DPIUtil.getZoomForAutoscaleProperty(initialNativeZoom)) {
+			destroyHandle(entry.getValue());
+			return true;
+		}
+		return false;
+	});
+}
+
+private void destroyHandle(long handle) {
+	if (type == SWT.ICON) {
+		OS.DestroyIcon (handle);
+	} else {
+		OS.DeleteObject (handle);
+	}
+}
+
 /**
  * Compares the argument to the receiver, and returns true
  * if they represent the <em>same</em> object using a class

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

@@ -86,6 +86,7 @@ private Path(Device device, int zoom) {
 	if (handle == 0) SWT.error(SWT.ERROR_NO_HANDLES);
 	zoomLevelToHandle.put(initialZoom, handle);
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -133,6 +134,7 @@ public Path (Device device, Path path, float flatness) {
 	initialZoom = path.initialZoom;
 	zoomLevelToHandle.put(initialZoom, handle);
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -172,6 +174,7 @@ private Path(Device device, PathData data, int zoom) {
 	this(device, zoom);
 	if (data == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
 	init(data);
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -438,6 +441,18 @@ void destroy() {
 	zoomLevelToHandle.clear();
 }
 
+@Override
+void destroyHandlesExcept(Set<Integer> zoomLevels) {
+	zoomLevelToHandle.entrySet().removeIf(entry -> {
+		final Integer zoom = entry.getKey();
+		if (!zoomLevels.contains(zoom) && zoom != initialZoom) {
+			Gdip.GraphicsPath_delete(entry.getValue());
+			return true;
+		}
+		return false;
+	});
+}
+
 /**
  * Replaces the first four elements in the parameter with values that
  * describe the smallest rectangle that will completely contain the

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

@@ -90,6 +90,7 @@ public Pattern(Device device, Image image) {
 	initialZoom = DPIUtil.getDeviceZoom();
 	setImageHandle(image, initialZoom);
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -183,6 +184,7 @@ public Pattern(Device device, float x1, float y1, float x2, float y2, Color colo
 	this.image = null;
 	initialZoom = DPIUtil.getDeviceZoom();
 	initializeSize(initialZoom);
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 long getHandle(int zoom) {
@@ -260,21 +262,7 @@ void setImageHandle(Image image, int zoom) {
 @Override
 void destroy() {
 	for (long handle: zoomLevelToHandle.values()) {
-		int type = Gdip.Brush_GetType(handle);
-		switch (type) {
-			case Gdip.BrushTypeSolidColor:
-				Gdip.SolidBrush_delete(handle);
-				break;
-			case Gdip.BrushTypeHatchFill:
-				Gdip.HatchBrush_delete(handle);
-				break;
-			case Gdip.BrushTypeLinearGradient:
-				Gdip.LinearGradientBrush_delete(handle);
-				break;
-			case Gdip.BrushTypeTextureFill:
-				Gdip.TextureBrush_delete(handle);
-				break;
-		}
+		destroyHandle(handle);
 	}
 	zoomLevelToHandle.clear();
 	if (bitmapDestructor != null) {
@@ -283,6 +271,36 @@ void destroy() {
 	}
 }
 
+@Override
+void destroyHandlesExcept(Set<Integer> zoomLevels) {
+	zoomLevelToHandle.entrySet().removeIf(entry -> {
+		final Integer zoom = entry.getKey();
+		if (!zoomLevels.contains(zoom) && zoom != initialZoom) {
+			destroyHandle(entry.getValue());
+			return true;
+		}
+		return false;
+	});
+}
+
+private void destroyHandle(long handle) {
+	int type = Gdip.Brush_GetType(handle);
+	switch (type) {
+		case Gdip.BrushTypeSolidColor:
+			Gdip.SolidBrush_delete(handle);
+			break;
+		case Gdip.BrushTypeHatchFill:
+			Gdip.HatchBrush_delete(handle);
+			break;
+		case Gdip.BrushTypeLinearGradient:
+			Gdip.LinearGradientBrush_delete(handle);
+			break;
+		case Gdip.BrushTypeTextureFill:
+			Gdip.TextureBrush_delete(handle);
+			break;
+	}
+}
+
 /**
  * Returns <code>true</code> if the Pattern has been disposed,
  * and <code>false</code> otherwise.

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

@@ -84,6 +84,7 @@ public Region (Device device) {
 	zoomToHandle.put(initialZoom, handle);
 	if (handle == 0) SWT.error(SWT.ERROR_NO_HANDLES);
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 /**
@@ -227,6 +228,18 @@ void destroy () {
 	operations.clear();
 }
 
+@Override
+void destroyHandlesExcept(Set<Integer> zoomLevels) {
+	zoomToHandle.entrySet().removeIf(entry -> {
+		final Integer zoom = entry.getKey();
+		if (!zoomLevels.contains(zoom) && zoom != initialZoom) {
+			OS.DeleteObject(entry.getValue());
+			return true;
+		}
+		return false;
+	});
+}
+
 /**
  * Compares the argument to the receiver, and returns true
  * if they represent the <em>same</em> object using a class

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

@@ -145,6 +145,7 @@ public Transform (Device device, float m11, float m12, float m21, float m22, flo
 	if (handle == 0) SWT.error(SWT.ERROR_NO_HANDLES);
 	zoomLevelToHandle.put(initialZoom, handle);
 	init();
+	this.device.registerResourceWithZoomSupport(this);
 }
 
 static float[] checkTransform(float[] elements) {
@@ -159,6 +160,18 @@ void destroy() {
 	zoomLevelToHandle.clear();
 }
 
+@Override
+void destroyHandlesExcept(Set<Integer> zoomLevels) {
+	zoomLevelToHandle.entrySet().removeIf(entry -> {
+		final Integer zoom = entry.getKey();
+		if (!zoomLevels.contains(zoom) && zoom != initialZoom) {
+			Gdip.Matrix_delete(entry.getValue());
+			return true;
+		}
+		return false;
+	});
+}
+
 /**
  * Fills the parameter with the values of the transformation matrix
  * that the receiver represents, in the order {m11, m12, m21, m22, dx, dy}.

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Control.java

@@ -4899,6 +4899,7 @@ LRESULT WM_DPICHANGED (long wParam, long lParam) {
 	// Map DPI to Zoom and compare
 	int newNativeZoom = DPIUtil.mapDPIToZoom (OS.HIWORD (wParam));
 	if (getDisplay().isRescalingAtRuntime()) {
+		Device.win32_destroyUnusedHandles(getDisplay());
 		int oldNativeZoom = nativeZoom;
 		if (newNativeZoom != oldNativeZoom) {
 			DPIUtil.setDeviceZoom (newNativeZoom);