[GTK] Fix loading 1 pixel wide RGB images with glycin

Since gdk-pixbuf delegates decoding to glycin, the rowstride of a pixbuf
is no longer padded to 4 bytes, so a 1 pixel wide RGB image has a stride
of 3. The loader passed that stride as scanline pad, and cloning the PNG
ImageData then failed its minimum data length check, which assumes a
4 byte pad. Repack the rows to the standard 4 byte pad instead.

Fixes #3545

Assisted-by: multiple AI agents and layers of automated tooling 🤖

Author: vogella

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/internal/NativeImageLoader.java

@@ -225,8 +225,18 @@ private static ImageData pixbufToImageData(long pixbuf) {
 		 * width in bytes of the last row to copy raw pixbuf data.
 		 */
 		int lastRowWidth = width * ((n_channels * bits_per_sample + 7) / 8);
-		byte[] srcData = new byte[stride * height];
-		C.memmove(srcData, pixels, stride * (height - 1) + lastRowWidth);
+		// The rowstride is not always 4-byte aligned (e.g. with glycin), but ImageData expects that
+		int bytesPerLine = (lastRowWidth + 3) / 4 * 4;
+		byte[] srcData = new byte[bytesPerLine * height];
+		if (stride == bytesPerLine) {
+			C.memmove(srcData, pixels, stride * (height - 1) + lastRowWidth);
+		} else {
+			byte[] row = new byte[lastRowWidth];
+			for (int y = 0; y < height; y++) {
+				C.memmove(row, pixels + (long) y * stride, lastRowWidth);
+				System.arraycopy(row, 0, srcData, y * bytesPerLine, lastRowWidth);
+			}
+		}
 		/*
 		 * Note: GdkPixbuf only supports 3/4 n_channels and 8 bits_per_sample, This
 		 * means all images are of depth 24 / depth 32. This means loading images will
@@ -236,7 +246,7 @@ private static ImageData pixbufToImageData(long pixbuf) {
 		 * See https://www.eclipse.org/articles/Article-SWT-images/graphics-resources.html#PaletteData
 		 */
 		PaletteData palette = new PaletteData(0xFF0000, 0xFF00, 0xFF);
-		ImageData imgData = new ImageData(width, height, bits_per_sample * n_channels, palette, stride, srcData);
+		ImageData imgData = new ImageData(width, height, bits_per_sample * n_channels, palette, 4, srcData);
 		if (hasAlpha) {
 			byte[] alphaData = imgData.alphaData = new byte[width * height];
 			for (int y = 0, offset = 0, alphaOffset = 0; y < height; y++) {

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

@@ -36,6 +36,7 @@
 import org.eclipse.swt.graphics.ImageLoaderEvent;
 import org.eclipse.swt.graphics.ImageLoaderListener;
 import org.eclipse.swt.graphics.PaletteData;
+import org.eclipse.swt.graphics.RGB;
 import org.eclipse.swt.internal.DPIUtil.ElementAtZoom;
 import org.eclipse.swt.internal.NativeImageLoader;
 import org.eclipse.swt.widgets.Display;
@@ -246,6 +247,26 @@ public void test_loadSingleFrameGifReportedAsAnimation_bug3404() throws IOExcept
 	}
 }
 
+/**
+ * Regression test for https://github.com/eclipse-platform/eclipse.platform.swt/issues/3545
+ *
+ * A one pixel wide RGB image has a row stride of 3 bytes when gdk-pixbuf decodes through glycin.
+ */
+@Test
+public void test_loadOnePixelWideRgbPng_bug3545() throws IOException {
+	ImageData imageData;
+	try (InputStream in = getClass().getResourceAsStream("rgb_1x3.png")) {
+		assertNotNull(in, "Test resource rgb_1x3.png not found");
+		imageData = new ImageData(in);
+	}
+	assertEquals(1, imageData.width);
+	assertEquals(3, imageData.height);
+	RGB[] expected = { new RGB(0x00, 0x35, 0x6a), new RGB(0x5b, 0x90, 0xc5), new RGB(0xb6, 0xeb, 0x20) };
+	for (int y = 0; y < expected.length; y++) {
+		assertEquals(expected[y], imageData.palette.getRGB(imageData.getPixel(0, y)), "Wrong pixel in row " + y);
+	}
+}
+
 /* custom */
 boolean loaderListenerCalled;
 }