[GTK] Fix the image size cache never hitting at zoom != 100

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

@@ -913,9 +913,14 @@ void drawImage(Image srcImage, int srcX, int srcY, int srcWidth, int srcHeight,
 	/* Refresh Image as per zoom level, if required. */
 	srcImage.refreshImageForZoom ();
 
-	ImageData srcImageData = srcImage.getImageData();
-	int imgWidth = srcImageData.width;
-	int imgHeight = srcImageData.height;
+	int imgWidth = srcImage.width;
+	int imgHeight = srcImage.height;
+	if (imgWidth == -1 || imgHeight == -1) {
+		/* Images wrapped around a native handle carry no dimensions, see Image.gtk_new. */
+		ImageData srcImageData = srcImage.getImageData();
+		imgWidth = srcImageData.width;
+		imgHeight = srcImageData.height;
+	}
 	if (srcWidth == 0 && srcHeight == 0) {
 		srcWidth = imgWidth;
 		srcHeight = imgHeight;

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

@@ -970,12 +970,17 @@ void destroy() {
 
 private class CachedImageAtSize {
 	private Image image;
+	/** Size in pixels the cached image was requested at; the image itself carries points. */
+	private int requestedWidth = -1;
+	private int requestedHeight = -1;
 
 	public void destroy() {
 		if (image != null) {
 			image.dispose();
 			image = null;
 		}
+		requestedWidth = -1;
+		requestedHeight = -1;
 	}
 
 	private Optional<Image> refresh(int destWidth, int destHeight) {
@@ -987,12 +992,16 @@ private Optional<Image> refresh(int destWidth, int destHeight) {
 			destroy();
 			Optional<Image> imageAtSize = loadImageAtSize(scaledWidth, scaledHeight);
 			image = imageAtSize.orElse(null);
+			if (image != null) {
+				requestedWidth = scaledWidth;
+				requestedHeight = scaledHeight;
+			}
 			return imageAtSize;
 		}
 	}
 
 	private boolean isReusable(int width, int height) {
-		return image != null && image.height == height && image.width == width;
+		return image != null && requestedHeight == height && requestedWidth == width;
 	}
 
 	private Optional<Image> loadImageAtSize(int destWidth, int destHeight) {

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

@@ -30,6 +30,9 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.lang.ref.WeakReference;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
 
@@ -59,6 +62,7 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 
@@ -72,6 +76,9 @@ public class Test_org_eclipse_swt_graphics_GC {
 
 private static final int IMAGE_SIZE = 200;
 
+@TempDir
+static Path tempFolder;
+
 @BeforeEach
 public void setUp() {
 	display = Display.getDefault();
@@ -1208,6 +1215,60 @@ RGB getRealRGB(Color color) {
 	return palette.getRGB(pixel);
 }
 
+/**
+ * Drawing reads the image dimensions from the image itself. Obtaining them through
+ * ImageData used to decode the file again on every draw at a device zoom other than 100.
+ */
+@Test
+public void test_drawImage_doesNotReReadImageFileAtNonDefaultZoom() throws IOException {
+	Path file = tempFolder.resolve("volatile-collapseall.png");
+	Files.copy(SwtTestUtil.getPath("collapseall.png", tempFolder), file);
+	int previousDeviceZoom = DPIUtil.getDeviceZoom();
+	Image fileImage = null;
+	try {
+		DPIUtil.setDeviceZoom(200);
+		gc.dispose();
+		gc = new GC(image);
+		fileImage = new Image(display, file.toString());
+		ImageData beforeDelete = drawToFreshTarget(fileImage);
+		assertFalse(Arrays.equals(blankTargetData(), beforeDelete.data), "the reference draw produced no pixels");
+
+		Files.delete(file);
+
+		ImageData afterDelete = drawToFreshTarget(fileImage);
+		ImageDataTestHelper.assertImageDataEqual(beforeDelete, afterDelete, beforeDelete);
+		gc.drawImage(fileImage, 0, 0);
+	} finally {
+		if (fileImage != null) {
+			fileImage.dispose();
+		}
+		DPIUtil.setDeviceZoom(previousDeviceZoom);
+		Files.deleteIfExists(file);
+	}
+}
+
+private byte[] blankTargetData() {
+	Image target = new Image(display, IMAGE_SIZE, IMAGE_SIZE);
+	try {
+		return target.getImageData().data;
+	} finally {
+		target.dispose();
+	}
+}
+
+private ImageData drawToFreshTarget(Image source) {
+	Rectangle bounds = source.getBounds();
+	Image target = new Image(display, IMAGE_SIZE, IMAGE_SIZE);
+	GC targetGc = new GC(target);
+	try {
+		targetGc.drawImage(source, 0, 0, bounds.width, bounds.height, 0, 0, bounds.width * 2, bounds.height * 2);
+		return target.getImageData();
+	} finally {
+		targetGc.dispose();
+		target.dispose();
+	}
+}
+
 private void executeWithNonDefaultDeviceZoom(Runnable executable) {
 	int previousDeviceZoom = DPIUtil.getDeviceZoom();
 	DPIUtil.setDeviceZoom(200);

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

@@ -1224,5 +1224,43 @@ public void test_gcOnImageGcDrawer_imageDataAtNonDeviceZoom() {
 	}
 }
 
+/**
+ * The size cache must hit at any device zoom. Comparing the requested size in pixels
+ * against the cached image's size in points made every scaled draw a miss at zoom != 100.
+ */
+@Test
+public void test_drawImageAtSize_cacheIsReusedAtNonDefaultZoom() throws IOException {
+	Path file = tempFolder.resolve("cached-collapseall.svg");
+	Files.copy(Path.of(getPath("collapseall.svg")), file);
+	int originalDeviceZoom = DPIUtil.getDeviceZoom();
+	Image image = null;
+	Image target = null;
+	GC gc = null;
+	try {
+		DPIUtil.setDeviceZoom(200);
+		image = new Image(display, file.toString());
+		target = new Image(display, 64, 64);
+		gc = new GC(target);
+		gc.drawImage(image, 0, 0, 20, 20);
+
+		// a second draw at the same size must come from the cache, so the file is not needed
+		Files.delete(file);
+
+		gc.drawImage(image, 0, 0, 20, 20);
+	} finally {
+		if (gc != null) {
+			gc.dispose();
+		}
+		if (target != null) {
+			target.dispose();
+		}
+		if (image != null) {
+			image.dispose();
+		}
+		DPIUtil.setDeviceZoom(originalDeviceZoom);
+		Files.deleteIfExists(file);
+	}
+}
+
 }