A strict check 200% image data is double the size of 100% image data

A strict check to be used only for debugging means, this ensures the
imageData is scaled linearly for 100 and 200 zooms.

Author: arunjose696

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

@@ -299,9 +299,12 @@ private static ImageData autoScaleImageData (Device device, final ImageData imag
 	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 -> {
+			return (zoom == defaultZoomLevel) ? imageData : null;
+		});
 		ImageGcDrawer drawer =  new ImageGcDrawer() {
 			@Override
 			public void drawOn(GC gc, int imageWidth, int imageHeight) {
@@ -315,7 +318,7 @@ 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

@@ -610,10 +610,29 @@ 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) {
+		SWT.error(SWT.ERROR_INVALID_ARGUMENT, null, "ImageData should be linearly scaled across zooms.");
+	}
+}
+
 /**
  * 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

@@ -1031,13 +1031,15 @@ 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_graphics_ImageData.java

@@ -24,6 +24,9 @@
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.fail;
+import static org.junit.Assume.assumeNotNull;
+import static org.junit.Assume.assumeTrue;
 
 import java.io.IOException;
 import java.io.InputStream;
@@ -32,8 +35,10 @@
 
 import org.eclipse.swt.SWT;
 import org.eclipse.swt.SWTException;
+import org.eclipse.swt.graphics.GC;
 import org.eclipse.swt.graphics.Image;
 import org.eclipse.swt.graphics.ImageData;
+import org.eclipse.swt.graphics.ImageDataProvider;
 import org.eclipse.swt.graphics.PaletteData;
 import org.eclipse.swt.graphics.RGB;
 import org.eclipse.swt.tests.graphics.ImageDataTestHelper;
@@ -799,6 +804,40 @@ public void test_setAlphaIII() {
 	assertSWTProblem("Incorrect exception thrown for putWidth < 0", SWT.ERROR_INVALID_ARGUMENT, ex);
 }
 
+@Test
+public void test_ImageCreationFailsWithNonScalingImageDataProviderWhenStrictCheckIsEnabled() {
+	assumeNotNull(System.getProperty("org.eclipse.swt.internal.enableStrictChecks"));
+	Display display = Display.getDefault();
+	GC gc = new GC(display);
+	try {
+		ImageDataProvider wrongDataProvider = (zoom) -> new ImageData(16, 16, 32, new PaletteData());
+		Image image = new Image(display, wrongDataProvider);
+		image.dispose();
+		fail("Expected an exception due to non-linearly scaled image data provider");
+	} catch (IllegalArgumentException | SWTException e) {
+	} finally {
+		gc.dispose();
+		display.dispose();
+	}
+}
+
+@Test
+public void test_ImageCreationSucceedsWithNonScalingImageDataProviderWhenStrictCheckIsDisabled() {
+	assumeTrue(System.getProperty("org.eclipse.swt.internal.enableStrictChecks") == null);
+	Display display = Display.getDefault();
+	GC gc = new GC(display);
+	try {
+		ImageDataProvider wrongDataProvider = (zoom) -> new ImageData(16, 16, 32, new PaletteData());
+		Image image = new Image(display, wrongDataProvider);
+		image.dispose();
+	} catch (IllegalArgumentException | SWTException e) {
+		fail("Image creation is expected to succeed without strict checks, even for a non-scaling ImageDataProvider.");
+	} finally {
+		gc.dispose();
+		display.dispose();
+	}
+}
+
 @Test
 public void test_setPixelIII() {
 	int value;

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

@@ -55,15 +55,13 @@ 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));
+			return (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));
+			return (zoom == 100) ? new ImageData(getPath("corrupt.svg")) : null;
 		};
 		SWTException e = assertThrows(SWTException.class,
 				() -> new Image(Display.getDefault(), corruptImageDataProvider));