Aliased names for glCreateShader and glCreateShaderObjectARB

[Carl Worth]

José Fonseca <jose.r.fonseca at gmail.com> writes:
>> I recently found a program mixing calls to glCreateShaderObjectARB and
>> glUseProgram, (rather than sticking to consistent use of
>> glUseProgramObjectARB).

And yesterday I found myself uselessly going through the process of
debugging the exact same failure mode (with the exact same program).

Apparently, I failed to hold on to the quick hack I had made to make
apitrace work with this program. (And, also, I failed to get anything
upstream to fix this.) So here I hope to document things better and
hopefully move toward getting something upstream.

> Concerning this app, what about masking out support for
> GL_ARB_shader_objects when tracing? Does that yield a lean trace that
> only uses the core entrypoints?

We tried this yesterday, and unfortunately it didn't cause any behavior
change in the program. So clearly there's a bug in the program. We'll
try to talk to the application authors and get things fixed, (might as
well not doing any mixing of the calls at all). So hopefully this
problem will go away for this particular application.

>> I implemented a quick hack with a single table for all of the above uses
>> and that fixed our particular problem, (particularly since I know that
>> our implementation uses a single namespace for all of the above).

Here's that quick hack, (so that if I lose it again, I can find it in my
email):

diff --git a/retrace/glretrace_gl.cpp b/retrace/glretrace_gl.cpp
index 425634d..d11478a 100644
--- a/retrace/glretrace_gl.cpp
+++ b/retrace/glretrace_gl.cpp
@@ -17,7 +17,8 @@ static retrace::map<GLuint> _list_map;
 static retrace::map<GLuint> _texture_map;
 static retrace::map<GLuint> _query_map;
 static retrace::map<GLuint> _buffer_map;
-static retrace::map<GLuint> _program_map;
+#define _program_map _handleARB_map
+#define _shader_map _handleARB_map
 static retrace::map<GLuint> _shader_map;
 static std::map<GLhandleARB, retrace::map<GLint> > _location_map;
 static retrace::map<GLuint> _programARB_map;

(And, in generating this patch I realized why I lost it earlier. This is
an edit of a generated file that's untracked by git.)

As described above, this patch is not portable since it assumes that the
OpenGL implementation uses a single table for both shaders and
programs. So this works for me on Mesa, but it's definitely not
guaranteed to work on other implementations.

>> Eric pointed out that an implementation supporting
>> glCreateShaderObjectARB is effectively forced to have a single namespace
>> for shaders and programs, (so that one map is the correct answer). But
>> an implementation without this support might have separate namespaces,
>> (in which case we would want one shader_map and one program_map). But in
>> no case do we actually want three tables.

I've now started work on this better solution. See the patch attached
below.

This patch seems to work in the testing I've done. It has some code to
support an OpenGL implementation without support for the
GL_ARB_shader_objects extension but I have not tested that.

Meanwhile, the code is not ideal. It has a couple of layering
violations, where code in retrace.py is generating GL-specific code, and
one piece of the code generation has a fixed string "_handleARB_map"
where similar code goes through a function call to construct a string
such as "_program_map".

I don't think either of these issue cause any problem today, (the
supportsARBShaderObjects Boolean is initialized to false so that the new
conditions should have no effect on non-GL code). But they do perhaps
make the code slightly more fragile than desired. If anyone has a better
solution, (a GL-specific SwizzledValueRegistrator, etc??), I'd be happy
to see it.

In the meantime, I should at least be able to get my work done with this
commit in place in my own tree, and if I lose it again, I should be able
to find it which this detailed description here on the list.

-Carl

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