[Mesa-dev] Status of GL_ARB_separate_shader_objects? I would like to help.

gregory hainaut gregory.hainaut at gmail.com
Sat Mar 23 14:05:54 PDT 2013

On Fri, 22 Mar 2013 15:44:07 -0700
Matt Turner <mattst88 at gmail.com> wrote:

> On Fri, Mar 22, 2013 at 1:00 PM, gregory hainaut
> <gregory.hainaut at gmail.com> wrote:
> > * GenProgramPipelines doesn't create object!
> > ... Spec extract:
> > These names are marked as used, for the purposes of GenBuffers only,
> >   but they acquire buffer state only when they are first bound with
> >   BindBuffer (see below), just as if they were unused.
> > ...
> >
> > Basically any command (like BindBuffer) that access the pipeline
> > will create the pipeline. It seems like vertex array object. From an
> > implemention point of view it seems much easier to create the object
> > during GenProgramPipelines call. However I don't know if
> > IsProgramPipeline must return FALSE if the object was never really
> > created (bind) like VAO.
> This is a weird part of the spec. After glGen* (but before glBind*)
> the associated glIs* function usually returns false. It's something
> that no one but conformance tests seem to care about. See commit
> fd93d55141f11069fb76a9b377ad1af88d0ecdd3 (in Mesa) for how to fix this
> kind of thing.
> I said "usually" above because there is some inconsistency. The
> ARB_sampler_objects spec says that the act of calling glIsSampler()
> actually creates the object.
> It looks like for ARB_separate_shader_objects that glGen* followed by
> glIs* should return false (like VAOs).

Ok. Thanks for the example. I updated my code and create a  piglit
test. By the way, fglrx doesn't follow this behavior, dunno for nvidia.

On the mix UseProgram/BindProgramPipeline subjet. 
I try to search the spec for additional info and found this example:
Issue 4:
        When a non-zero program is passed to UseProgram, any subsequent
        uniform updates will affect that program, ignoring the active
program in any bound pipeline object.  For example:

          glActiveProgram(1, 2);
          glUniform1f(0, 3.0);          // affects program 2
          glUniform1f(0, 3.0);          // affects program 3
          glUniform1f(0, 3.0);          // affects program 2

So after glUseProgram(0), the state of the pipeline is restored (or they
forgot to update this part of the spec when they clarify the priority
rule), at least the ActiveProgram. Anyway, I write an extensive piglit
test and check the behavior on fglrx. Here the outcome, glUseProgram(0)
destroy current program state, the pipeline need to be rebound
again for any shader based rendering. However ActiveProgram is restored
as the previous example! Any opinion is welcome, run the test on
nvidia? Mimic AMD behavior?


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