Implemented a more robust and transparent scheme for making

sure that iconphoto images are not blended with a black background.

1 files changed, 11 insertions, 16 deletions

diff --git a/macosx/tkMacOSXImage.c b/macosx/tkMacOSXImage.c
index 02e8c54..adcb0f5 100644
--- a/macosx/tkMacOSXImage.c
+++ b/macosx/tkMacOSXImage.c
@@ -160,25 +160,20 @@ XGetImage(
     unsigned int bytes_per_row, size, row, n, m;
     unsigned int scalefactor=1, scaled_height=height, scaled_width=width;
     NSWindow *win = TkMacOSXDrawableWindow(drawable);
-    TkWindow *winPtr = TkMacOSXGetTkWindow(win);
+    MacDrawable *macDraw = ((MacDrawable*)drawable);
     static enum {unknown, no, yes} has_retina = unknown;
 
-    if (win && !winPtr) {
+    if (macDraw->flags & TK_DO_NOT_BLEND) {
 	/*
-	 * If this drawable has an associated NSWindow but does not have an
-	 * associated Tk window then it must be a dock icon.  We are being
-	 * called by TkImgPhotoDisplay because it is displaying a photoimage
-	 * with an alpha channel, e.g. one generated from a png file, as the
-	 * dock icon.  It is asking us to create a pixmap for the rectangle
-	 * where the image will be drawn so that it can blend the photoimage
-	 * with its background using the alpha values.  But in the case of a
-	 * dock icon, that background will be black, not transparent as it
-	 * should be.
-	 *
-	 * By returning NULL here, we force TkImgPhotoDisplay to give up on
-	 * trying to blend, and just copy the image pixels to the screen.  That
-	 * does the right thing for a dock icon, as it happens.
-	 */ 
+	 * When called by TkImgPhotoDisplay we are being asked to return a
+	 * background image to be blended with the photoimage using its alpha
+	 * channel, if it has one.  Returning NULL here makes TkImgPhotoDisplay
+	 * simply copy the image data, including the alpha channel, rather than
+	 * do any blending.  For example, when creating an iconphoto from a
+	 * photoimage with transparency we will be passed a newly created
+	 * pixmap filled with black pixels.  These should not be blended with
+	 * the pixels in the photoimage.
+	 */
 	return NULL;
     }