I have never understood why Mesa has gl_context::Visual and gl_framebuffer::Visual. The Mesa code also allows a non-matching doublebuffer setting between the two. libEGL also always uses a singlebuffered config for pixmaps and pbuffers even if the context config is doublebuffered.
Marek On Tue, Apr 30, 2019, 1:25 PM Adam Jackson <a...@redhat.com> wrote: > 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 > >
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