etnaviv: work around miComputeCompositeRegion()

The comment above miComputeCompositeRegion() says:
/*
 * returns FALSE if the final region is empty.  Indistinguishable from
 * an allocation failure, but rendering ignores those anyways.
 */

This is not true in at least Xorg 1.17 - it returns TRUE despite the
region being clipped away, and the final region being empty:

{extents = {x1 = 0, y1 = 0, x2 = 0, y2 = 0}, data = 0x1fda60 <RegionEmptyData>}

This appears to be due to the RegionIntersect() in miClipPictureSrc()
returning TRUE when RegionIntersect() determines that the region is
empty.  The failing case is:

miComputeCompositeRegion(&region, pSrc, 0, pDst, 0, 0, 0, 0, 0, 0, 1920, 1080)

where pSrc->clientClip is:

{extents = {x1 = -1000, y1 = -1000, x2 = -995, y2 = -995}, data = 0x0}

Signed-off-by: Russell King <rmk@arm.linux.org.uk>

1 files changed, 8 insertions, 1 deletions

diff --git a/etnaviv/etnaviv_render.c b/etnaviv/etnaviv_render.c
index 46bc181..a3abb3b 100644
--- a/etnaviv/etnaviv_render.c
+++ b/etnaviv/etnaviv_render.c
@@ -477,7 +477,14 @@ static Bool etnaviv_compute_composite_region(RegionPtr region,
 
 	return miComputeCompositeRegion(region, pSrc, pMask, pDst,
 					xSrc, ySrc, xMask, yMask,
-					xDst, yDst, width, height);
+					xDst, yDst, width, height) &&
+		/* Xorg 1.17 can return TRUE, despite the region being
+		 * empty, which goes against the comment immediately
+		 * above miComputeCompositeRegion().  It appears to be
+		 * a pixman bug, with pixman_region_intersect() returning
+		 * TRUE even though the resulting region is empty.
+		 */
+		RegionNotEmpty(region);
 }
 
 static Bool etnaviv_Composite_Clear(PicturePtr pDst, struct etnaviv_de_op *op)