XCopyArea clip bug

Alexander Larsson alexl at redhat.com
Wed Feb 4 04:38:55 PST 2009

I found what I think is a bug in XCopyArea. 

If you copy a pixmap to a window and some of the copied area is outside
the pixmap then that area in the destination window is cleared to the
background color (and possibly graphics exposes are sent).

If the GC has a clip region set so that the destination area that would
contain data from outside the pixmap is clipped out, then I would expect
it to not be cleared. 

However, that is not the case right now, even the clipped out area has
the destination cleared to the window background.

I'm attaching an xlib example.

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