Is there an advantage of using glGetProgramResourceLocation instead glGetUniformLocation?

Question

When I was looking at OpenGL 4.5 specification, I noticed you could get a uniform's location by calling:

glGetProgramResourceLocation(program, GL_UNIFORM, name);

Which is very similar to:

glGetUniformLocation(program, name);

I was wondering if there's any advantage of using the former instead of the latter.

Answer 1

OpenGL's program introspection APIs were not very well designed. They grew semi-organically from the original 3DLabs GLSL proposal. But the original design was predicated on querying only attribute/uniform locations and uniform resources.

As GLSL grew, it added a lot more kinds of resources: UBOs, shader subroutines, SSBOs, and others. Also, people realized that querying the fragment shader output variables was also useful.

What this led to was a Frankenstein's API. Every time they added a new resource to introspect, they had to add a couple more API entrypoints. In OpenGL 4.3, they finally decided to just overhaul the whole system.

The generic program introspection system can query everything the old queries could do. And the specification redefines the old queries in terms of the new, generic system. But now, when you add a new resource to OpenGL, you only need to add a few new enumerators to the existing generic queries, not whole API functions.

So long as you're using recent versions of OpenGL, you ought to use the newer query mechanism. If for no other reason than to keep your code looking more uniform.

Answer 2

The former is equivalent to the later.

See OpenGL 4.6 API Core Profile Specification; 7.6. UNIFORM VARIABLES; page 134:

Additionally, several dedicated commands are provided to query properties of active uniforms. The command

int GetUniformLocation( uint program, const char *name );

is equivalent to

GetProgramResourceLocation(program, UNIFORM, name);