Fix bug 137295 -- gaps in images sometimes. We need to work around a CopyDeepMask bug when the clip region is complex, by restricting the clip region to the image destination rectangle. r=sdagley, sr=scc.

gfx/src/mac/nsImageMac.cpp

@@ -826,16 +826,31 @@ void nsImageMac::CopyBitsWithMask(const BitMap* srcBits, const BitMap* maskBits,
 {
   if (maskBits)
   {
-    StRegionFromPool    clipRegion;
+    StRegionFromPool    origClipRegion;
     
     if (inDrawingToPort)
     {
-      // we need to pass in the clip region, even if it doesn't intersect the image, to avoid a bug
+      // We need to pass in the clip region, even if it doesn't intersect the image, to avoid a bug
       // on Mac OS X that causes bad image drawing (see bug 137295).
-      ::GetClip(clipRegion);
+      ::GetClip(origClipRegion);
+      
+      // There is a bug in the OS that causes bad image drawing if the clip region in
+      // the destination port is complex (has holes in??), which hits us on pages with iframes.
+      // To work around this, temporarily set the clip to the intersection of the clip 
+      // and this image (which, most of the time, will be rectangular). See bug 137295.
+      
+      StRegionFromPool newClip;
+      ::CopyRgn(origClipRegion, newClip);
+      ::SetRectRgn(newClip, destRect.left, destRect.top, destRect.right, destRect.bottom);
+      ::SetClip(newClip);
     }
-    
-    ::CopyDeepMask(srcBits, maskBits, destBits, &srcRect, &maskRect, &destRect, srcCopy, inDrawingToPort ? clipRegion : (RgnHandle)nsnull);
+
+    ::CopyDeepMask(srcBits, maskBits, destBits, &srcRect, &maskRect, &destRect, srcCopy, nsnull);
+
+    if (inDrawingToPort)
+    {
+      ::SetClip(origClipRegion);
+    }    
   }
   else
   {