Enable check for using GC on Image in unsupported use cases

With this change, warnings will be logged when strict checks are enabled
and a GC is initialized for an image in unsupported cases:
1. images whose scaled variants are not derived via scaling from an
   original version but are retrieved from a central data source (like
   ImageDataProvider or ImageFileNameProvider)
2. images for which handles in other zoom values have already been
   created such that drawing on them will only be applied to one of
   those handles

Author: ShahzaibIbrahim

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

@@ -1707,6 +1707,9 @@ private long configureGC(GCData data, int zoom) {
 		SWT.error(SWT.ERROR_INVALID_ARGUMENT);
 	}
 
+	if(Device.strictChecks) {
+		checkImageTypeForValidCustomDrawing(zoom);
+	}
 	/* Create a compatible HDC for the device */
 	long hDC = device.internal_new_GC(null);
 	long imageDC = OS.CreateCompatibleDC(hDC);
@@ -1729,6 +1732,18 @@ private long configureGC(GCData data, int zoom) {
 	return imageDC;
 }
 
+private void checkImageTypeForValidCustomDrawing(int zoom) {
+	String replacementInfo = "It should be created with an ImageGcDrawer (see SWT Snippet 384).";
+	if (imageProvider instanceof ImageDataProviderWrapper || imageProvider instanceof ImageFileNameProviderWrapper) {
+		String message = "***WARNING: Image initialized with ImageDataProvider or ImageFileNameProvider is not supposed to be modified.";
+		System.err.println(message + " " + replacementInfo);
+	} else if (!zoomLevelToImageHandle.isEmpty()
+			&& (zoomLevelToImageHandle.size() != 1 || !zoomLevelToImageHandle.containsKey(zoom))) {
+		String message = "***WARNING: Images with handles created for multiple zooms should not be modified. ";
+		System.err.println(message + " " + replacementInfo);
+	}
+}
+
 /**
  * Invokes platform specific functionality to dispose a GC handle.
  * <p>

examples/org.eclipse.swt.snippets/Snippets.md

@@ -215,6 +215,7 @@ To contribute a new snippet, [create a snippet contribution as a pull request](h
 - [draw an image at various zoom/dpi levels](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet367.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet367.png "Preview for Snippet 367")
 - [draw a disabled/grayed image at various zoom levels](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet382.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet382.png "Preview for Snippet 382")
 - [compare algorithms for rendering disabled images](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet384.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet384.png "Preview for Snippet 384")
+- [draw an image with watermark using ImageGcProvider](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet385.java) – [(preview)](https://github.com/eclipse-platform/eclipse.platform.swt/blob/master/examples/org.eclipse.swt.snippets/previews/Snippet385.png "Preview for Snippet 385")
 
 ### **ImageData**
 - [display an animated GIF](https://github.com/eclipse-platform/eclipse.platform.swt/tree/master/examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet141.java)

examples/org.eclipse.swt.snippets/previews/Snippet385.png

@@ -0,0 +1,88 @@
+/*******************************************************************************
+ * 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.snippets;
+
+import org.eclipse.swt.*;
+import org.eclipse.swt.graphics.*;
+import org.eclipse.swt.widgets.*;
+
+/**
+ * Demonstration how to custom draw images
+ * <p>
+ * Snippet to show how to draw on an image loaded from the file system which has
+ * multiple variants for different zoom levels. Mainly relevant on Windows, as
+ * it uses the Windows-only monitor-specific scaling mode.
+ * <p>
+ * For a list of all SWT example snippets see
+ * http://www.eclipse.org/swt/snippets/
+ * </p>
+ */
+public class Snippet385 {
+
+	public static void main(String[] args) {
+		System.setProperty("swt.autoScale.updateOnRuntime", "true");
+		Display display = new Display();
+		Shell shell = new Shell(display);
+		shell.setText("Watermark over Image using GC");
+		shell.setSize(1200, 900);
+
+		final ImageFileNameProvider filenameProvider = zoom -> {
+			String path = null;
+			switch (zoom) {
+			case 150:
+				path = "resources/Snippet385/red.jpeg";
+				break;
+			case 100:
+				path = "resources/Snippet385/black.jpg";
+				break;
+			default:
+				path = "resources/Snippet385/black.jpg";
+			}
+			return path;
+		};
+		Image loadedImage = new Image(display, filenameProvider);
+
+		int width = loadedImage.getBounds().width;
+		int height = loadedImage.getBounds().height;
+
+		Image composedImage = new Image(display, (gc, iX, iY) -> {
+			gc.drawImage(loadedImage, 0, 0);
+
+			gc.setForeground(display.getSystemColor(SWT.COLOR_WHITE));
+			Font font = new Font(display, "Arial", 24, SWT.BOLD);
+			gc.setFont(font);
+			gc.setAlpha(128); // semi-transparent
+			String watermark = "WATERMARK";
+			Point extent = gc.textExtent(watermark);
+			int x = (width - extent.x) / 2;
+			int y = (height - extent.y) / 2;
+			gc.drawText(watermark, x, y, SWT.DRAW_TRANSPARENT);
+			font.dispose();
+		}, width, height);
+
+		shell.addPaintListener(e -> {
+			e.gc.drawImage(composedImage, 0, 0);
+		});
+
+		shell.open();
+		while (!shell.isDisposed()) {
+			if (!display.readAndDispatch())
+				display.sleep();
+		}
+
+		loadedImage.dispose();
+		composedImage.dispose();
+		display.dispose();
+	}
+}