CODEWITHSUNDEEP
openglshader
Zebrafish
Zebrafish

Reputation: 13886

OpenGL binding shader stages and programs confusion

I am currently using shader pipeline objects in OpenGL (separable shader stages) along with the older style single programs with glUseProgram(). I'm wondering, in the documentation it says:

If there is a current program object established by `glUseProgram`, 
the bound program pipeline object has no effect on rendering or uniform updates.

This is confusing to me because I seem to be able to do:

glUseProgram(6); // Render using the single program
glBindProgramPipeline(pipeline_ID);
glUseProgramStages(pipeline_ID, GL_VERTEX_SHADER_BIT, shaderID);
glUseProgramStages(pipeline_ID, GL_FRAGMENT_SHADER_BIT, shaderID);

without first setting glUseProgram(0) before calling glUseProgramPipeline. The documentation I thought implied that it wouldn't work, but I can render fine like this. Is it necessary to set glUseProgram(0) before calling glBindProgramPipeline?

Upvotes: 0

Views: 633

Answers (1)

Nicol Bolas
Nicol Bolas

Reputation: 473272

has no effect on rendering or uniform updates

Nothing in the code you have shown deals with "rendering" or "uniform updates". If you call glUniform, it will go to program object 6, not to anything in the pipeline (unless 6 happens to be in the pipeline). If you render, you will use the shaders in program object 6, not those in the pipeline (again, unless 6 happens to be in the pipeline).

So long as there is a program in use, the pipeline will not affect rendering.

It should also be noted that glUseProgramStages doesn't affect pipeline_ID because it is bound to the context. It affects that pipeline because you pass it as a parameter. You didn't have to bind it first. Indeed, the only reason to bind a pipeline is to render with it; all of its state setting functions use DSA-style.

Upvotes: 2

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