Thanks for the more elaborated explanation. I think I understand now. Ideally the GLSL shader code is compiled once and sent to the GPU and used as-is to rende

Thanks for the more elaborated explanation. I think I understand now. Ideally the GLSL shader code is compiled once and sent to the GPU and used as-is to render many frames. But if you use the stateful OpenGL APIs to send instructions from the CPU side during rendering you can invalidate the shader code that was compiled. It had not occurred to me because the library I am using makes it difficult to do that, encouraging setting the state up front and running the shaders against the buffers as a single "render" call.