Without this, we end up throwing errors on code along these lines when
rendering using single-buffering:
GLint att;
glGetIntegerv(GL_READ_BUFFER, &att);
glGetFramebufferAttachmentParameteriv(GL_READ_FRAMEBUFFER, att, ...);
This is because we internally translate GL_BACK (which is what
glGetIntegerv returned) to GL_FRONT, which we don't handle in the
Desktop GL case. So let's start handling it.
This fixes the GLTF-GL33.gtf21.GL2FixedTests.buffer_color.blend_color
test for me.
Fixes: e6ca6e587e ("mesa: Handle pbuffers in desktop GL framebuffer attachment queries")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6815>
9e13a16c97