In the best practice, what code should appear at the top of a GLSL shader?

What are the four types of clearable buffers?

What happens when an object to be drawn is not within the current viewport?

What function is required in every GLSL shader program?

Does OpenGL perform clipping for objects not within the current viewport?

What is "core" versus "compatibility" styles of writing OpenGL applications?

Does gluProject use the current matrix stack?

Which function has an unsigned byte variant? (taking GLubyte as arguments)

What will be the size of the quad drawn by the following code on the screen?

OpenGL can draw convex polygons. Can it draw non-convex ones?

Is the following code correct?