[Win32] Add check that ImageDataProvider returns linearly scaled data

A strict check to be used only for debugging means, which ensures the
imageData returned by an ImageDataProvider is scaled linearly for 100
and 200 zooms.

Author: arunjose696

bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/internal/DPIUtil.java

@@ -150,9 +150,10 @@ public static ImageData autoScaleImageData (Device device, final ImageData image
 	int height = imageData.height;
 	int scaledWidth = Math.round (width * scaleFactor);
 	int scaledHeight = Math.round (height * scaleFactor);
+	int defaultZoomLevel = 100;
 	boolean useSmoothScaling = isSmoothScalingEnabled() && imageData.getTransparencyType() != SWT.TRANSPARENCY_MASK;
 	if (useSmoothScaling) {
-		Image original = new Image (device, (ImageDataProvider) zoom -> imageData);
+		Image original = new Image(device, (ImageDataProvider) zoom -> (zoom == defaultZoomLevel) ? imageData : null);
 		ImageGcDrawer drawer =  new ImageGcDrawer() {
 			@Override
 			public void drawOn(GC gc, int imageWidth, int imageHeight) {
@@ -166,7 +167,7 @@ public int getGcStyle() {
 			}
 		};
 		Image resultImage = new Image (device, drawer, scaledWidth, scaledHeight);
-		ImageData result = resultImage.getImageData (100);
+		ImageData result = resultImage.getImageData (defaultZoomLevel);
 		original.dispose ();
 		resultImage.dispose ();
 		return result;

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

@@ -612,10 +612,33 @@ public Image(Device device, ImageDataProvider imageDataProvider) {
 		SWT.error(SWT.ERROR_INVALID_ARGUMENT, null,
 				": ImageDataProvider [" + imageDataProvider + "] returns null ImageData at 100% zoom.");
 	}
+	if (Device.strictChecks) {
+		validateLinearScaling(imageDataProvider);
+	}
 	init();
 	this.device.registerResourceWithZoomSupport(this);
 }
 
+private void validateLinearScaling(ImageDataProvider provider) {
+	final int baseZoom = 100;
+	final int scaledZoom = 200;
+	final int scaleFactor = scaledZoom / baseZoom;
+	ImageData baseImageData = provider.getImageData(baseZoom);
+	ImageData scaledImageData = provider.getImageData(scaledZoom);
+
+	if (scaledImageData == null) {
+		return;
+	}
+
+	if (scaledImageData.width != scaleFactor * baseImageData.width
+			|| scaledImageData.height != scaleFactor * baseImageData.height) {
+		System.err.println(String.format(
+				"***WARNING: ImageData should be linearly scaled across zooms but size is (%d, %d) at 100%% and (%d, %d) at 200%%.",
+				baseImageData.width, baseImageData.height, scaledImageData.width, scaledImageData.height));
+		new Error().printStackTrace(System.err);
+	}
+}
+
 /**
  * The provided ImageGcDrawer will be called on demand whenever a new variant of the
  * Image for an additional zoom is required. Depending on the OS-specific implementation

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_graphics_Image.java

@@ -1043,13 +1043,15 @@ public void test_imageDataIsCached() {
 public void test_imageDataSameViaDifferentProviders() {
 	assumeFalse("Cocoa generates inconsistent image data", SwtTestUtil.isCocoa);
 	String imagePath = getPath("collapseall.png");
-	ImageFileNameProvider imageFileNameProvider = __ -> {
-		return imagePath;
+	ImageFileNameProvider imageFileNameProvider = zoom -> {
+		return (zoom == 100) ? imagePath : null;
 	};
-	ImageDataProvider dataProvider = __ -> {
-		try (InputStream imageStream = Files.newInputStream(Path.of(imagePath))) {
-			return new ImageData(imageStream);
-		} catch (IOException e) {
+	ImageDataProvider dataProvider = zoom -> {
+		if (zoom == 100) {
+			try (InputStream imageStream = Files.newInputStream(Path.of(imagePath))) {
+				return new ImageData(imageStream);
+			} catch (IOException e) {
+			}
 		}
 		return null;
 	};

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_internal_SVGRasterizer.java

@@ -54,17 +54,11 @@ public void test_ConstructorLorg_eclipse_swt_graphics_Device_ImageFileNameProvid
 
 	@Test
 	public void test_ConstructorLorg_eclipse_swt_graphics_Device_ImageDataProvider() {
-		ImageDataProvider validImageDataProvider = zoom -> {
-			String fileName = "collapseall.svg";
-			return new ImageData(getPath(fileName));
-		};
+		ImageDataProvider validImageDataProvider = zoom -> (zoom == 100) ? new ImageData(getPath("collapseall.svg")) : null;
 		Image image = new Image(Display.getDefault(), validImageDataProvider);
 		image.dispose();
 
-		ImageDataProvider corruptImageDataProvider = zoom -> {
-			String fileName = "corrupt.svg";
-			return new ImageData(getPath(fileName));
-		};
+		ImageDataProvider corruptImageDataProvider = zoom -> (zoom == 100) ? new ImageData(getPath("corrupt.svg")) : null;
 		SWTException e = assertThrows(SWTException.class,
 				() -> new Image(Display.getDefault(), corruptImageDataProvider));
 		assertSWTProblem("Incorrect exception thrown for provider with corrupt images", SWT.ERROR_INVALID_IMAGE, e);