Problem in miClipPictureSrc?

Soeren Sandmann sandmann at
Fri Oct 2 07:07:31 PDT 2009

"Kim Woelders" <kim at> writes:

> Commit 128cd03eecacc6d5c5903d59a11966dcf3697bf1 causes trouble with
> clip  regions in the e16 WM composite manager (e.g. during fade-out).

This marks the second recorded use of source clipping in the history
of the Render extension.

> The problems are fixed by attached patch. Not sure if this is the
> proper  solution though...

The intent of this code is to shift the client clip into destination
coordinates, then clip against it. Translating by clipOrigin.x/y
converts from region coordinates to source coordinates, and dx/dy is
supposed to bring it into destination coordinates.

The problem with the commit I think is that I was thinking of dx/dy as
the amount the destination is shifted, when it actually is how much
the source is shifted.

If so, the real fix would be:

> @@ -318,14 +318,14 @@ miClipPictureSrc (RegionPtr	pRegion,
>  	Bool result;
>  	pixman_region_translate ( pPicture->clientClip,
> -				  pPicture->clipOrigin.x - dx,
> -				  pPicture->clipOrigin.y - dy);
> +				  dx - pPicture->clipOrigin.x,
> +				  dy - pPicture->clipOrigin.y);

+                                 pPicture->clipOrigin.x + dx,
+                                 pPicture->clipOrigin.y + dy,

and a similar correction after the intersection.

I'd be interested in whether the same bug exists with the vesa driver
(or another unaccelerated one).


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