[Mesa-dev] [PATCH] egl_dri2: Allow both 24 and 32 bit X visuals for RGBA configs

Eric Anholt eric at anholt.net
Fri Nov 7 11:32:04 PST 2014

Pekka Paalanen <ppaalanen at gmail.com> writes:

> On Thu, 06 Nov 2014 13:01:03 -0800
> Ian Romanick <idr at freedesktop.org> wrote:
>> I thought Eric and Chad already NAKed it in bugzilla.  The problem is
>> that applications ask for an RGBA visual for GL blending.  They use the
>> alpha channel to generate their images, but the final alpha values are,
>> basically, random... and the composited result would be pure garbage.
> Reading
> https://bugs.freedesktop.org/show_bug.cgi?id=67676#c5
> "We should certainly be exposing EGLConfigs that match up to the rgba
> visual, though, so you can find it when you try." - Eric
> To me that sounds like Eric would accept having the visuals there
> in additional configs (as long as they are sorted after the otherwise
> equivalent xRGB configs?). Eric, would you like to confirm your current
> opinion?

What I believe we want:

Somebody just requesting RGBA with ChooseConfig doesn't end up forced
into the depth-32 (blending) X visual.  This is the most important.

There is some mechanism for somebody that does want the depth 32 visual
to get an EGL config to draw to it.  This is important but secondary to
not breaking everything else, and them having to jump through hoops is
reasonable but probably avoidable.
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