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(release/25.1) fb: Don't widen the planemask over padding bits when ROOTLESS_SAFEALPHA is set #3591

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(release/25.1) fb: Don't widen the planemask over padding bits when ROOTLESS_SAFEALPHA is set #3591

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17 changes: 17 additions & 0 deletions fb/fbgc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -152,7 +152,24 @@ fbValidateGC(GCPtr pGC, unsigned long changes, DrawablePtr pDrawable)
pPriv->fg = pGC->fgPixel & mask;
pPriv->bg = pGC->bgPixel & mask;

/*
* Widening the planemask to cover the padding bits lets the blit and
* fill paths take their "all ones" shortcuts, but it also makes them
* write those bits. A rootless server keeps the alpha channel of its
* on screen windows opaque by clearing the alpha bits from the
* planemask (see miext/rootless/rootlessGC.c), and it can only do so
* from its own ValidateGC. mi revalidates the GC in the middle of a
* drawing operation for dashed lines, dashed arcs and opaque text,
* and by then the rootless funcs have been unwrapped by the damage
* layer, so that reassertion never happens. Leave the padding bits
* alone when they aren't part of the depth.
*/
#ifdef ROOTLESS_SAFEALPHA
if (pDrawable->depth == pDrawable->bitsPerPixel &&
(pGC->planemask & depthMask) == depthMask)
#else
if ((pGC->planemask & depthMask) == depthMask)
#endif
pPriv->pm = mask;
else
pPriv->pm = pGC->planemask & mask;
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