Allow to test for loading image at zoom and fix faulty Win32 image load

The ImageLoader and FileFormat implementations currently combine the
check whether an image can be provided at a specific scale value and the
provision of an image in the scale itself. In case a consumer wants to
only test whether an image can be provided at a specific scale, it needs
to request that image at that scale, even if it will not be used later
one, e.g., because it cannot be provided in the required scale.

With this change, ImageLoader and FileFormat provide separate methods
for validating whether an image can be retrieved at a specific zoom
(such as from an SVG) and the retrieval of the image itself. This is
employed by the Cocoa Image implementation to avoid unnecessary load
operations and in the Win32 Image implementation to correct erroneous
scaling from an already initialized handle instead of loading at proper
zoom (such as for an SVG). In addition, this fixes a faulty reuse of the
same stream in the Cocoa Image implementation at the same place.

Author: HeikoKlare

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

@@ -20,7 +20,6 @@
 
 import org.eclipse.swt.*;
 import org.eclipse.swt.internal.*;
-import org.eclipse.swt.internal.DPIUtil.*;
 import org.eclipse.swt.internal.cocoa.*;
 import org.eclipse.swt.internal.graphics.*;
 import org.eclipse.swt.internal.image.*;
@@ -695,8 +694,12 @@ public Image(Device device, InputStream stream) {
 	NSAutoreleasePool pool = null;
 	if (!NSThread.isMainThread()) pool = (NSAutoreleasePool) new NSAutoreleasePool().alloc().init();
 	try {
-		initWithSupplier(zoom -> ImageDataLoader.load(stream, FileFormat.DEFAULT_ZOOM, zoom));
+		byte[] input = stream.readAllBytes();
+		initWithSupplier(zoom -> ImageDataLoader.canLoadAtZoom(new ByteArrayInputStream(input), FileFormat.DEFAULT_ZOOM, zoom),
+				zoom -> ImageDataLoader.load(new ByteArrayInputStream(input), FileFormat.DEFAULT_ZOOM, zoom).element());
 		init();
+	} catch (IOException e) {
+		SWT.error(SWT.ERROR_INVALID_ARGUMENT, e);
 	} finally {
 		if (pool != null) pool.release();
 	}
@@ -741,7 +744,10 @@ public Image(Device device, String filename) {
 	try {
 		if (filename == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
 		initNative(filename);
-		if (this.handle == null) initWithSupplier(zoom -> ImageDataLoader.load(filename, FileFormat.DEFAULT_ZOOM, zoom));
+		if (this.handle == null) {
+			initWithSupplier(zoom -> ImageDataLoader.canLoadAtZoom(filename, FileFormat.DEFAULT_ZOOM, zoom),
+					zoom -> ImageDataLoader.load(filename, FileFormat.DEFAULT_ZOOM, zoom).element());
+		}
 		init();
 	} finally {
 		if (pool != null) pool.release();
@@ -795,15 +801,13 @@ public Image(Device device, ImageFileNameProvider imageFileNameProvider) {
 			id id = NSImageRep.imageRepWithContentsOfFile(NSString.stringWith(filename2x));
 			NSImageRep rep = new NSImageRep(id);
 			handle.addRepresentation(rep);
-		} else {
+		} else if (ImageDataLoader.canLoadAtZoom(filename, 100, 200)) {
 			// Try to natively scale up the image (e.g. possible if it's an SVG)
-			ElementAtZoom<ImageData> imageData2x = ImageDataLoader.load(filename, 100, 200);
-			if (imageData2x.zoom() == 200) {
-				alphaInfo_200 = new AlphaInfo();
-				NSBitmapImageRep rep = createRepresentation (imageData2x.element(), alphaInfo_200);
-				handle.addRepresentation(rep);
-				rep.release();
-			}
+			ImageData imageData2x = ImageDataLoader.load(filename, 100, 200).element();
+			alphaInfo_200 = new AlphaInfo();
+			NSBitmapImageRep rep = createRepresentation (imageData2x, alphaInfo_200);
+			handle.addRepresentation(rep);
+			rep.release();
 		}
 	} finally {
 		if (pool != null) pool.release();
@@ -1484,17 +1488,11 @@ void init(ImageData image) {
 	handle.setCacheMode(OS.NSImageCacheNever);
 }
 
-private void initWithSupplier(Function<Integer, ElementAtZoom<ImageData>> zoomToImageData) {
-	ElementAtZoom<ImageData> imageData = zoomToImageData.apply(DPIUtil.getDeviceZoom());
-	ImageData imageData2x = null;
-	if (imageData.zoom() == 200) {
-		imageData2x = imageData.element();
-	}
-	if (imageData.zoom() != 100) {
-		imageData = zoomToImageData.apply(100);
-	}
-	init(imageData.element());
-	if (imageData2x != null) {
+private void initWithSupplier(Function<Integer, Boolean> canLoadAtZoom, Function<Integer, ImageData> zoomToImageData) {
+	ImageData imageData = zoomToImageData.apply(100);
+	init(imageData);
+	if (canLoadAtZoom.apply(200)) {
+		ImageData imageData2x = zoomToImageData.apply(200);
 		alphaInfo_200 = new AlphaInfo();
 		NSBitmapImageRep rep = createRepresentation (imageData2x, alphaInfo_200);
 		handle.addRepresentation(rep);

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

@@ -37,12 +37,20 @@ public static ImageData load(String filename) {
 		return data[0];
 	}
 
+	public static boolean canLoadAtZoom(InputStream stream, int fileZoom, int targetZoom) {
+		return ImageLoader.canLoadAtZoom(stream, fileZoom, targetZoom);
+	}
+
 	public static ElementAtZoom<ImageData> load(InputStream stream, int fileZoom, int targetZoom) {
 		List<ElementAtZoom<ImageData>> data = new ImageLoader().load(stream, fileZoom, targetZoom);
 		if (data.isEmpty()) SWT.error(SWT.ERROR_INVALID_IMAGE);
 		return data.get(0);
 	}
 
+	public static boolean canLoadAtZoom(String filename, int fileZoom, int targetZoom) {
+		return ImageLoader.canLoadAtZoom(filename, fileZoom, targetZoom);
+	}
+
 	public static ElementAtZoom<ImageData> load(String filename, int fileZoom, int targetZoom) {
 		List<ElementAtZoom<ImageData>> data = new ImageLoader().load(filename, fileZoom, targetZoom);
 		if (data.isEmpty()) SWT.error(SWT.ERROR_INVALID_IMAGE);

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

@@ -163,6 +163,11 @@ List<ElementAtZoom<ImageData>> load(InputStream stream, int fileZoom, int target
 	return images;
 }
 
+static boolean canLoadAtZoom(InputStream stream, int fileZoom, int targetZoom) {
+	if (stream == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
+	return FileFormat.canLoadAtZoom(new ElementAtZoom<>(stream, fileZoom), targetZoom);
+}
+
 /**
  * Loads an array of <code>ImageData</code> objects from the
  * file with the specified name. Throws an error if either
@@ -196,6 +201,16 @@ List<ElementAtZoom<ImageData>> load(String filename, int fileZoom, int targetZoo
 	return null;
 }
 
+static boolean canLoadAtZoom(String filename, int fileZoom, int targetZoom) {
+	if (filename == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
+	try (InputStream stream = new FileInputStream(filename)) {
+		return canLoadAtZoom(stream, fileZoom, targetZoom);
+	} catch (IOException e) {
+		SWT.error(SWT.ERROR_IO, e);
+	}
+	return false;
+}
+
 /**
  * Saves the image data in this ImageLoader to the specified stream.
  * The format parameter can have one of the following values:

bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/internal/image/FileFormat.java

@@ -136,6 +136,10 @@ public static List<ElementAtZoom<ImageData>> load(ElementAtZoom<InputStream> is,
 	return fileFormat.loadFromStream(stream, is.zoom(), targetZoom);
 }
 
+public static boolean canLoadAtZoom(ElementAtZoom<InputStream> is, int targetZoom) {
+	return is.zoom() == targetZoom  || isDynamicallySizableFormat(is.element());
+}
+
 /**
  * Write the device independent image array stored in the specified loader
  * to the specified output stream using the specified file format.

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

@@ -2212,13 +2212,20 @@ private class ImageFileNameProviderWrapper extends BaseImageProviderWrapper<Imag
 	@Override
 	ImageData getImageData(int zoom) {
 		ElementAtZoom<String> fileForZoom = DPIUtil.validateAndGetImagePathAtZoom(provider, zoom);
+
+		// Load at appropriate zoom via loader
+		if (fileForZoom.zoom() != zoom && ImageDataLoader.canLoadAtZoom(fileForZoom.element(), fileForZoom.zoom(), zoom)) {
+			ElementAtZoom<ImageData> imageDataAtZoom = ImageDataLoader.load(fileForZoom.element(), fileForZoom.zoom(), zoom);
+			return adaptImageDataIfDisabledOrGray(imageDataAtZoom.element());
+		}
+
+		// Load at file zoom (native or via loader) and rescale
 		ImageHandle nativeInitializedImage;
 		if (zoomLevelToImageHandle.containsKey(fileForZoom.zoom())) {
 			nativeInitializedImage = zoomLevelToImageHandle.get(fileForZoom.zoom());
 		} else {
 			nativeInitializedImage = initNative(fileForZoom.element(), fileForZoom.zoom());
 		}
-
 		ElementAtZoom<ImageData> imageDataAtZoom;
 		if (nativeInitializedImage == null) {
 			imageDataAtZoom = ImageDataLoader.load(fileForZoom.element(), fileForZoom.zoom(), zoom);