[Bug 80033] [sna] Occasional artifacts on window borders (theme dependent)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=80033

--- Comment #23 from Chris Wilson <chris at chris-wilson.co.uk> ---
(In reply to comment #22)
> (In reply to comment #20)
> > If you are certain it is a repeating pattern, then it the BLT being loaded
> > up with garbage. The BLT takes an 8x8 pattern to be repeated, so it that
> > matches the repeat distance I know it is still junk being fed into that
> > command. :|
> > 
> > Have you refined your test? Could you?
> 
> Never saw a periodicity longer than 8px; sometimes shorter, but that could
> be just because the garbage has a pattern.
> 
> I've replaced the offending xpm with a 3px/4px wide one. With the 3px one I
> couldn't see any stripes, only the right edge of the bottom border shows
> sometimes a wrong pixel. With 4px it's basically the same as with 2px (maybe
> a bit less frequent) and a period of 8px again.

That confirms it is the NxM conversion to 8x8 that is still upset. Did you test

commit c257c936b42b92827b784cee0b7caa54e6040364
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Wed Jun 18 22:15:42 2014 +0100

    sna: Fix modulus for partial conversion of tiles to 8x8 patterns

?

> And another observation (tested with commit
> d49f53cc00258e3b1e1a898c02e219b336716002, because it's much easier to
> reproduce): The stripes appear if the bottom border is >1009px (or 1013 if
> one includes the corner pixmaps).

I believe that is just the theme deciding to use a staging pixmap for wide
outlines. (Incorrectly, I might add since the hardware is more efficient doing
the operation in place twice than once to a pixmap then copying it.)

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