OpenGL, how to set up GLSL version?

Question

My system's default version for OpenGL and GLSL using freeglut is 4.1, also using glew there is no problem with its initialization, shader compilation and linking, and execution.

This default version happens when I don't specify glutInitContextVersion, glutInitContextFlags or glutInitContextProfile, then my shaders work correct.

Regardless I have support to this version, I would like to provide a 3.3 alternative. When I use the glut context specifying the 3.3 version, the application starts with no errors, glew doesn't complain. My shaders are suppose to use the GLSL 3.3 version, then I set the line

#version 330

But when my shaders are compiled, OpenGL complains with an invalid enumerant message. I tried removing this line or setting it to another version but I still get the same error. After all initialization has been properly done, i ask for the OpenGL version and I get the right 3.3, but for the GLSL version am still getting the default 4.1.

glGetString(GL_SHADING_LANGUAGE_VERSION);

Please correct me if am right, I guess this version is overwritten by the version line in the shaders code. I wonder if there is a chance to initialize the context specifying the GLSL version too?

Answer 1

I finally solved it. If I set the core profile along with the compatibility mode

glutInitContextProfile(GLUT_CORE_PROFILE | GLUT_COMPATIBILITY_PROFILE);

OpenGL commands from 2.1 version won't be recognized. This goes against the information provided in the tutorials. Anyways by only setting the GLUT_COMPATIBILITY_PROFILE it works, using 3.3 or greater version.