On 03/23/2013 02:05 PM, gregory hainaut wrote:
On Fri, 22 Mar 2013 15:44:07 -0700
Matt Turner <matts...@gmail.com> wrote:
On Fri, Mar 22, 2013 at 1:00 PM, gregory hainaut
<gregory.hain...@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:
glUseProgram(0);
glBindProgramPipeline(1);
glActiveProgram(1, 2);
glUniform1f(0, 3.0); // affects program 2
glUseProgram(3);
glUniform1f(0, 3.0); // affects program 3
glUseProgram(0);
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?
There are a few places in GL that behave this way. There are two
separate pieces of state that may be used. In this case, either the
UseProgram state or the BindProgramPipeline state. If UseProgram sets a
non-zero program, that state is used. Otherwise the BindProgramPipeline
state is used. In Mesa we generally handle this by having both sets of
state tracked in the context and a third _State field that's the one
actually in use.
Right now in the context we have
struct gl_shader_state Shader; /**< GLSL shader object state */
I think we'd expand this to
struct gl_shader_state Shader; /**< GLSL shader object state */
struct gl_shader_state SSOShader;
struct gl_shader_state *_Shader; /**< Points to ::Shader or
::SSOShader */
Or similar.
In this case, I think AMD's behavior is incorrect.
Cheers
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