[cairo-bugs] [Bug 84330] record-paint-alpha-clip-mask.xcb.rgb24 random failure

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=84330

--- Comment #5 from Uli Schlachter <psychon at znc.in> ---
Ok, I was wrong in that this is a bug in the server. The part that I forgot is:
Each render composite operation is only applied to the extents of the affected
region. This means that "no trapezoids" means "no extents" means "no effect"
and this is indeed a no-op. I don't know if the RENDER spec says that anywhere,
but it is how the implementation behaves.

The comment in the code indicates this with the comment saying "assert(trap
extents == extents)". Obviously (as this bug shows), this assert is wrong. It
might even still be wrong when we have a non-empty list of traps.

So my proposed fix is to just drop this optimisation completely.

I sent the following fix to the cairo mailing list:
https://lists.cairographics.org/archives/cairo/2016-July/027619.html

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