[win32] Set background color on all image handles

This commit adapts the win32 implementation of Image, so ensure that the
background color of an image is always set to all existing of later
created image handles. Currently all handles that are created after the
background color was set, would not receive the background color.

Author: akoch-yatta

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

@@ -117,6 +117,12 @@ public final class Image extends Resource implements Drawable {
 	 */
 	private int styleFlag = SWT.IMAGE_COPY;
 
+	/**
+	 * Sets the color to which to map the transparent pixel.
+	 * For further info see {@link #setBackground(Color)}
+	 */
+	private RGB backgroundColor;
+
 	/**
 	 * Attribute to cache current native zoom level
 	 */
@@ -1087,6 +1093,10 @@ public boolean equals (Object object) {
 public Color getBackground() {
 	if (isDisposed()) SWT.error(SWT.ERROR_GRAPHIC_DISPOSED);
 	if (transparentPixel == -1) return null;
+	if (backgroundColor != null) {
+		// if a background color was set explicitly, we use the cached color directly
+		return Color.win32_new(device, (backgroundColor.blue << 16) | (backgroundColor.green << 8) | backgroundColor.red);
+	}
 
 	/* Get the HDC for the device */
 	long hDC = device.internal_new_GC(null);
@@ -1838,33 +1848,10 @@ public void setBackground(Color color) {
 	if (isDisposed()) SWT.error(SWT.ERROR_GRAPHIC_DISPOSED);
 	if (color == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
 	if (color.isDisposed()) SWT.error(SWT.ERROR_INVALID_ARGUMENT);
-	zoomLevelToImageHandle.values().forEach(imageHandle -> setBackground(color, imageHandle.handle));
-}
-
-private void setBackground(Color color, long handle) {
 	if (transparentPixel == -1) return;
 	transparentColor = -1;
-
-	/* Get the HDC for the device */
-	long hDC = device.internal_new_GC(null);
-
-	/* Change the background color in the image */
-	BITMAP bm = new BITMAP();
-	OS.GetObject(handle, BITMAP.sizeof, bm);
-	long hdcMem = OS.CreateCompatibleDC(hDC);
-	OS.SelectObject(hdcMem, handle);
-	int maxColors = 1 << bm.bmBitsPixel;
-	byte[] colors = new byte[maxColors * 4];
-	int numColors = OS.GetDIBColorTable(hdcMem, 0, maxColors, colors);
-	int offset = transparentPixel * 4;
-	colors[offset] = (byte)color.getBlue();
-	colors[offset + 1] = (byte)color.getGreen();
-	colors[offset + 2] = (byte)color.getRed();
-	OS.SetDIBColorTable(hdcMem, 0, numColors, colors);
-	OS.DeleteDC(hdcMem);
-
-	/* Release the HDC for the device */
-	device.internal_dispose_GC(hDC, null);
+	backgroundColor = color.getRGB();
+	zoomLevelToImageHandle.values().forEach(imageHandle -> imageHandle.setBackground(backgroundColor));
 }
 
 private int getZoom() {
@@ -2403,9 +2390,37 @@ public ImageHandle(long handle, int zoom) {
 		this.handle = handle;
 		this.zoom = zoom;
 		updateBoundsInPixelsFromNative();
+		if (backgroundColor != null) {
+			setBackground(backgroundColor);
+		}
 		setImageMetadataForHandle(this, zoom);
 	}
 
+	private void setBackground(RGB color) {
+		if (transparentPixel == -1) return;
+
+		/* Get the HDC for the device */
+		long hDC = device.internal_new_GC(null);
+
+		/* Change the background color in the image */
+		BITMAP bm = new BITMAP();
+		OS.GetObject(handle, BITMAP.sizeof, bm);
+		long hdcMem = OS.CreateCompatibleDC(hDC);
+		OS.SelectObject(hdcMem, handle);
+		int maxColors = 1 << bm.bmBitsPixel;
+		byte[] colors = new byte[maxColors * 4];
+		int numColors = OS.GetDIBColorTable(hdcMem, 0, maxColors, colors);
+		int offset = transparentPixel * 4;
+		colors[offset] = (byte)color.blue;
+		colors[offset + 1] = (byte)color.green;
+		colors[offset + 2] = (byte)color.red;
+		OS.SetDIBColorTable(hdcMem, 0, numColors, colors);
+		OS.DeleteDC(hdcMem);
+
+		/* Release the HDC for the device */
+		device.internal_dispose_GC(hDC, null);
+	}
+
 	private void updateBoundsInPixelsFromNative() {
 		switch (type) {
 		case SWT.BITMAP: