[cairo-bugs] [Bug 99233] Nesting backgrounds with identical RGBA causes wrong colours to be drawn at innermost level

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99233

--- Comment #6 from Uli Schlachter <psychon at znc.in> ---
I took a brief look with xtrace:

Cairo "compresses" all the rectangles into a single FillRectangles request
(first one draws the white background, second one 'the rest')

000:<:001c: 24: RENDER-Request(139,4): CreatePicture pid=0x02800005
drawable=0x02800001 format=0x0000002a values={poly-mode=Imprecise(0x01)}
000:<:001d: 28: RENDER-Request(139,26): FillRectangles op=Src(0x01)
dst=0x02800005 red=0xffff green=0xffff blue=0xffff alpha=0xffff rects={x=0 y=0
w=100 h=100};
000:<:001e: 52: RENDER-Request(139,26): FillRectangles op=Over(0x03)
dst=0x02800005 red=0x0000 green=0x0000 blue=0x0000 alpha=0x3333 rects={x=10
y=10 w=80 h=80},{x=20 y=20 w=60 h=60},{x=30 y=30 w=40 h=40},{x=40 y=40 w=20
h=20};
000:>:001e: Event KeyPress(2) keycode=0x18 time=0x011b6157 root=0x00000117
event=0x02800001 child=None(0x00000000) root-x=967 root-y=785 event-x=966
event-y=744 state=Mod2 same-screen=true(0x01)

Since this does not happen in Xephyr, something in the X server is
mis-optimising this case, I guess.

@Chris: Now is your turn. I always fail to find the broken things in Xorg.

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