glamor woes with nouveau

[Olivier Fourdan]

Hi all,

I am trying to investigate an issue with Xwayland that affects pixmap
rendering only some hardware with nouveau (basically, older hardware).

Initally, I started looking into this because of reported black icons in
gtk2 (X11/Xwayland) apps in GNOME and RH bugzilla, and discovered that one
possible common factor is the use on nouveau:

  https://bugzilla.redhat.com/show_bug.cgi?id=1411447
  https://bugzilla.gnome.org/show_bug.cgi?id=776255

While trying to reproduce, I got a much worse problem where sometimes, the
entire window would appear completely garbled.

I initially thought of an issue in meda DRI driver, so I filed bug 99400
for this, but I am now wondering if this could be an issue with glamor
instead:

  https://bugs.freedesktop.org/show_bug.cgi?id=99400

Disabling glamor in Xwayland makes the problem go away, whereas Mesa with
debug enabled doesn't seem to complain much

Running Xwayland with GLAMOR_DEBUG=3 shows a few messages, most noticeably:

  glamor_composite_choose_shader: Unsupported source picture format.
    glamor_composite_with_shader: glamor_composite_choose_shader failed
                glamor_composite: from picts 0x25c8050:0x267ff60 48x48 /
0x25c3940:0x267ff60 48 x 48 (f,f)  to pict 0x2586890:0x2606e30 523x300 (f)

523x300 would match the size of the window where the entire background is
(apparently) random.

When the errors occur, we would end up in the fallback code
of glamor_composite() in glamor/glamor_render.c

But then I tried the same on intel hardware an get the exact same glamor
messages, and yet the rendering is fine on intel, so I am a bit confused,
could that be an issue with the fallback code in  glamor_composite() or is
it that the source pixmap being copied is actually garbled?

Any hint on how I could investigate that further?

Thanks
Olivier
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