[Mesa-dev] [PATCH] intel: Set ctx's drawbuffer according to drawables visual

[Benjamin Franzke]

2011/8/4 Brian Paul <brianp at vmware.com>:
> On 08/04/2011 06:31 AM, Benjamin Franzke wrote:
>>
>> Fixes https://bugs.freedesktop.org/show_bug.cgi?id=39588
>>
>> egl_dri2 creates contexts with a doubleBufferConfig when PIXMAP and
>> WINDOW bit is request, so _mesa_init_color sets DrawBuffer[0] to
>> GL_BACK.
>> If a pixmap surface is created egl_dri2 will use a single buffer config,
>> so MakeCurrent has to adjust DrawBuffer[0] to the current drawable.
>> ---
>>  src/mesa/drivers/dri/intel/intel_context.c |    6 ++++++
>>  1 files changed, 6 insertions(+), 0 deletions(-)
>>
>> diff --git a/src/mesa/drivers/dri/intel/intel_context.c
>> b/src/mesa/drivers/dri/intel/intel_context.c
>> index fe8be08..0eeffc0 100644
>> --- a/src/mesa/drivers/dri/intel/intel_context.c
>> +++ b/src/mesa/drivers/dri/intel/intel_context.c
>> @@ -970,6 +970,12 @@ intelMakeCurrent(__DRIcontext * driContextPriv,
>>         readFb = driReadPriv->driverPrivate;
>>         driContextPriv->dri2.draw_stamp = driDrawPriv->dri2.stamp - 1;
>>         driContextPriv->dri2.read_stamp = driReadPriv->dri2.stamp - 1;
>> +
>> +         if (fb->Visual.doubleBufferMode) {
>> +            intel->ctx.Color.DrawBuffer[0] = GL_BACK;
>> +         } else {
>> +            intel->ctx.Color.DrawBuffer[0] = GL_FRONT;
>> +         }
>>        }
>>
>>        intel_prepare_render(intel);
>
> This doesn't seem right to me.  We shouldn't be changing context state like
> that during a make-current() call.
>
> During context initialization we call _mesa_init_color() where we set
> ctx->Color.DrawBuffer[0] to either GL_BACK or GL_FRONT depending on the
> visual's double-buffer flag.  You might investigate why that's not doing the
> job.

Yea, I saw that, but the problem is it sets GL_BACK/GL_FRONT depending
on the contexts config,
which may be different from the config used for the drawable (as
described in the commit message).

So mixing configs could be defined as invalid, but its also allowed in
src/mesa/main/context.c:1324

Furthermore st/mesa also modifes the state in make_current, see
st_manager.c:781.

Any ideas where to put it instead?

>
> -Brian
>