[win32] Don't create a mask image when there is no mask

When setting an image for a shell, we try to convert the bitmap image
into icon to set the image on the top left of the shell. However we can
have icons which has no transparency. In this case we dont need to
create a transparency mask at all.

fixes #2638

Author: ShahzaibIbrahim

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Display.java

@@ -1180,32 +1180,39 @@ static long create32bitDIB (long hBitmap, int alpha, byte [] alphaData, int tran
 }
 
 static Image createIcon (Image image, int zoom) {
-	Device device = image.getDevice ();
+	Device device = image.getDevice();
 	ImageData data = image.getImageData(zoom);
-	if (data.alpha == -1 && data.alphaData == null) {
-		ImageData mask = data.getTransparencyMask ();
-		return new Image (device, data, mask);
-	}
-	int width = data.width, height = data.height;
-	long hMask, hBitmap;
-	long hDC = device.internal_new_GC (null);
-	long dstHdc = OS.CreateCompatibleDC (hDC), oldDstBitmap;
-	hBitmap = Display.create32bitDIB (Image.win32_getHandle(image, zoom), data.alpha, data.alphaData, data.transparentPixel);
-	hMask = OS.CreateBitmap (width, height, 1, 1, null);
-	oldDstBitmap = OS.SelectObject (dstHdc, hMask);
-	OS.PatBlt (dstHdc, 0, 0, width, height, OS.BLACKNESS);
-	OS.SelectObject (dstHdc, oldDstBitmap);
-	OS.DeleteDC (dstHdc);
-	device.internal_dispose_GC (hDC, null);
-	ICONINFO info = new ICONINFO ();
-	info.fIcon = true;
-	info.hbmColor = hBitmap;
-	info.hbmMask = hMask;
-	long hIcon = OS.CreateIconIndirect (info);
-	if (hIcon == 0) SWT.error(SWT.ERROR_NO_HANDLES);
-	OS.DeleteObject (hBitmap);
-	OS.DeleteObject (hMask);
-	return Image.win32_new (device, SWT.ICON, hIcon, zoom);
+	switch (data.getTransparencyType()) {
+	case SWT.TRANSPARENCY_MASK:
+	case SWT.TRANSPARENCY_PIXEL:
+		ImageData mask = data.getTransparencyMask();
+		return new Image(device, data, mask);
+	case SWT.TRANSPARENCY_ALPHA:
+	case SWT.NONE:
+	default:
+		int width = data.width, height = data.height;
+		long hMask, hBitmap;
+		long hDC = device.internal_new_GC(null);
+		long dstHdc = OS.CreateCompatibleDC(hDC), oldDstBitmap;
+		hBitmap = Display.create32bitDIB(Image.win32_getHandle(image, zoom), data.alpha, data.alphaData,
+				data.transparentPixel);
+		hMask = OS.CreateBitmap(width, height, 1, 1, null);
+		oldDstBitmap = OS.SelectObject(dstHdc, hMask);
+		OS.PatBlt(dstHdc, 0, 0, width, height, OS.BLACKNESS);
+		OS.SelectObject(dstHdc, oldDstBitmap);
+		OS.DeleteDC(dstHdc);
+		device.internal_dispose_GC(hDC, null);
+		ICONINFO info = new ICONINFO();
+		info.fIcon = true;
+		info.hbmColor = hBitmap;
+		info.hbmMask = hMask;
+		long hIcon = OS.CreateIconIndirect(info);
+		if (hIcon == 0)
+			SWT.error(SWT.ERROR_NO_HANDLES);
+		OS.DeleteObject(hBitmap);
+		OS.DeleteObject(hMask);
+		return Image.win32_new(device, SWT.ICON, hIcon, zoom);
+	}
 }
 
 long getTextSearchIcon(int size) {