Update ImageDataProvider contract

Clarify in the contract that ImageDataProvider implementations are
expected
to return linearly scaled ImageData based on the zoom level.

This commit also extends the strict checks for verifying linear scaling
to GTK and Cocoa implementations.

Author: arunjose696

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

@@ -850,6 +850,9 @@ public Image(Device device, ImageDataProvider imageDataProvider) {
 	try {
 		init (data, 100);
 		init ();
+		if (SWTInternalConstants.strictChecks) {
+			DPIUtil.validateLinearScaling(imageDataProvider);
+		}
 		ImageData data2x = imageDataProvider.getImageData (200);
 		if (data2x != null) {
 			alphaInfo_200 = new AlphaInfo();
@@ -1822,12 +1825,15 @@ public String toString () {
  * @noreference This method is not intended to be referenced by clients.
  */
 public static void drawScaled(GC gc, ImageData imageData, int width, int height, float scaleFactor) {
+	boolean originalStrictChecks = SWTInternalConstants.strictChecks;
+	SWTInternalConstants.strictChecks = false;
 	Image imageToDraw = new Image(gc.device, (ImageDataProvider) zoom ->  imageData);
 	gc.drawImage (imageToDraw, 0, 0, CocoaDPIUtil.pixelToPoint (width), CocoaDPIUtil.pixelToPoint (height),
 			/* E.g. destWidth here is effectively DPIUtil.autoScaleDown (scaledWidth), but avoiding rounding errors.
 			 * Nevertheless, we still have some rounding errors due to the point-based API GC#drawImage(..).
 			 */
 			0, 0, Math.round (CocoaDPIUtil.pixelToPoint (width * scaleFactor)), Math.round (CocoaDPIUtil.pixelToPoint (height * scaleFactor)));
+	SWTInternalConstants.strictChecks = originalStrictChecks;
 	imageToDraw.dispose();
 }
 

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

@@ -28,16 +28,31 @@ public interface ImageDataProvider {
 
 	/**
 	 * Returns the image data for the given zoom level.
-	 * <p>
-	 * If no image is available for a particular zoom level, this method should
-	 * return <code>null</code>. For <code>zoom == 100</code>, returning
-	 * <code>null</code> is not allowed, and SWT will throw an exception.
+	 *
+	 * <ul>
+     *   <li>
+     *     If no image is available for a particular zoom level, this method should
+     *     return <code>null</code>. For <code>zoom == 100</code>, returning
+     *     <code>null</code> is not allowed, and SWT will throw an exception.
+     *   </li>
+     *   <li>
+     *     Implementations are expected to return {@link ImageData} that is
+     *     <b>linearly scaled</b> with respect to the zoom level.
+     *     For example, if <code>getImageData(100)</code> returns an image of
+     *     width <code>w</code> and height <code>h</code>, then
+     *     <code>getImageData(200)</code> must return an {@link ImageData}
+     *     of width <code>2 * w</code> and height <code>2 * h</code>,
+     *     if a non-{@code null} result is returned.
+     *   </li>
+     * </ul>
+	 *
 	 *
 	 * @param zoom
 	 *            The zoom level in % of the standard resolution (which is 1
 	 *            physical monitor pixel == 1 SWT logical point). Typically 100,
 	 *            150, or 200.
-	 * @return the image data, or <code>null</code> if <code>zoom != 100</code>
+	 * @return the linearly scaled image data for the given zoom level,
+	 *         or <code>null</code> if <code>zoom != 100</code>
 	 *         and no image is available for the given zoom level.
 	 * @since 3.104
 	 */

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

@@ -223,6 +223,26 @@ public static int mapZoomToDPI (int zoom) {
 	return roundedDpi;
 }
 
+public static 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);
+	}
+}
+
 /**
  * Represents an element, such as some image data, at a specific zoom level.
  *

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

@@ -0,0 +1,20 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Yatta Solutions
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Yatta Solutions - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.swt.internal;
+
+public class SWTInternalConstants {
+
+	public static boolean strictChecks = System.getProperty("org.eclipse.swt.internal.enableStrictChecks") != null;
+
+}

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

@@ -672,6 +672,9 @@ public Image(Device device, ImageDataProvider imageDataProvider) {
 	currentDeviceZoom = DPIUtil.getDeviceZoom();
 	initFromImageDataProvider(currentDeviceZoom);
 	init ();
+	if (SWTInternalConstants.strictChecks) {
+		DPIUtil.validateLinearScaling(imageDataProvider);
+	}
 }
 
 /**
@@ -1583,12 +1586,15 @@ public String toString () {
  * @noreference This method is not intended to be referenced by clients.
  */
 public static void drawScaled(GC gc, ImageData imageData, int width, int height, float scaleFactor) {
+	boolean originalStrictChecks = SWTInternalConstants.strictChecks;
+	SWTInternalConstants.strictChecks = false;
 	Image imageToDraw = new Image(gc.device, (ImageDataProvider) zoom -> imageData);
 	gc.drawImage (imageToDraw, 0, 0, width, height,
 			/* E.g. destWidth here is effectively DPIUtil.autoScaleDown (scaledWidth), but avoiding rounding errors.
 			 * Nevertheless, we still have some rounding errors due to the point-based API GC#drawImage(..).
 			 */
 			0, 0, Math.round (width * scaleFactor), Math.round (height * scaleFactor));
+	SWTInternalConstants.strictChecks = originalStrictChecks;
 	imageToDraw.dispose();
 }
 

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Display.java

@@ -116,8 +116,6 @@
  */
 public class Display extends Device implements Executor {
 
-	static boolean strictChecks = System.getProperty("org.eclipse.swt.internal.enableStrictChecks") != null;
-
 	private static final int SLOT_IN_USE = -2;
 	private static final int LAST_TABLE_INDEX = -1;
 
@@ -880,7 +878,7 @@ void addWidget (long handle, Widget widget) {
 		widgetTable = newWidgetTable;
 	}
 	int index = freeSlot + 1;
-	if(strictChecks) {
+	if(SWTInternalConstants.strictChecks) {
 		long data = OS.g_object_get_qdata (handle, SWT_OBJECT_INDEX);
 		if(data > 0 && data != index) {
 			SWT.error(SWT.ERROR_INVALID_ARGUMENT, null, ". Potential leak of " + widget + debugInfoForIndex(data - 1));

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Shell.java

@@ -3258,7 +3258,7 @@ void deregister () {
 	if(shellHandle != 0 && !(disposed instanceof Shell)) {
 		SWT.error(SWT.ERROR_INVALID_RETURN_VALUE, null, ". Wrong widgetTable entry: " + disposed + " removed for shell: " + this + display.dumpWidgetTableInfo());
 	}
-	if(Display.strictChecks) {
+	if(SWTInternalConstants.strictChecks) {
 		Shell[] shells = display.getShells();
 		for (Shell shell : shells) {
 			if(shell == this) {

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

@@ -34,8 +34,6 @@
  */
 public abstract class Device implements Drawable {
 
-	static boolean strictChecks = System.getProperty("org.eclipse.swt.internal.enableStrictChecks") != null;
-
 	/* Debugging */
 	public static boolean DEBUG;
 	boolean debug = DEBUG;

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

@@ -210,7 +210,7 @@ private void validateGCState() {
 }
 
 void checkGC(int mask) {
-	if (Device.strictChecks) {
+	if (SWTInternalConstants.strictChecks) {
 		validateGCState();
 	}
 	int state = data.state;
@@ -4402,7 +4402,7 @@ private void init(Drawable drawable, GCData data, long hDC) {
 }
 
 private static int extractZoom(long hDC) {
-	if (Device.strictChecks) {
+	if (SWTInternalConstants.strictChecks) {
 		System.err.println("***WARNING: GC is initialized with a missing zoom. This indicates an "
 				+ "incompatible custom Drawable implementation.");
 	}

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

@@ -612,33 +612,13 @@ 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);
+	if (SWTInternalConstants.strictChecks) {
+		DPIUtil.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
@@ -850,12 +830,12 @@ public static long win32_getHandle (Image image, int zoom) {
  * @noreference This method is not intended to be referenced by clients.
  */
 public static void drawScaled(GC gc, ImageData imageData, int width, int height, float scaleFactor) {
-	boolean originalStrictChecks = Device.strictChecks;
-	Device.strictChecks = false;
+	boolean originalStrictChecks = SWTInternalConstants.strictChecks;
+	SWTInternalConstants.strictChecks = false;
 	Image imageToDraw = new Image(gc.device, (ImageDataProvider) zoom ->  imageData);
 	gc.drawImage (imageToDraw, 0, 0, width, height,
 			0, 0, Math.round (width * scaleFactor), Math.round (height * scaleFactor), false);
-	Device.strictChecks = originalStrictChecks;
+	SWTInternalConstants.strictChecks = originalStrictChecks;
 	imageToDraw.dispose();
 }
 
@@ -1752,7 +1732,7 @@ private long configureGC(GCData data, int zoom) {
 		SWT.error(SWT.ERROR_INVALID_ARGUMENT);
 	}
 
-	if (Device.strictChecks) {
+	if (SWTInternalConstants.strictChecks) {
 		checkImageTypeForValidCustomDrawing(zoom);
 	}
 	/* Create a compatible HDC for the device */