[Mesa-dev] [PATCH 2/3] mesa: fix pbuffers because internally they are front buffers

[Adam Jackson]

On Mon, 2019-04-29 at 20:35 -0400, Marek Olšák wrote:

> Yeah that's possible. The thing is that a GL context can have a
> doublebuffered config and begin with GL_BACK as the draw buffer, but
> MakeCurrent can set a pbuffer with a singlebuffered config and then
> nothing is rendered with Mesa because there is no back buffer. This
> case appears to work on NVIDIA.

Okay, that makes sense. Thanks for the explanation.

I think this is only true because of EGL_KHR_no_config_context? If the
context has a config, then you shouldn't be able to make a single-
buffered pbuffer current to a double-buffered context. EGL section
2.2's definition of compatibility includes having "color and ancillary
buffers of the same depth"; if you don't have a back buffer, then you
have zero bits of back buffer, and you would not be compatible with
non-zero bits of back buffer. I would think, anyway.

Now if you bind a single-buffered pbuffer to a no-config context,
obviously rendering should go to GL_FRONT.

- ajax