OpenGL - Samplers in opengl 3.1?

Question

I'm using samplers quite frequently in my application and everything has been working fine.

The problem is, I can only use opengl 3.1 on my laptop. According to the documentation, samplers are only available at opengl 3.3 or higher, but here's where I'm getting a bit confused.

I can use 'glGenSamplers' just fine, no errors are generated and the sampler ID seems fine as well. When using 'glBindSampler' on a valid texture, I get a 'GL_INVALID_VALUE​' error.

Can anyone clear this up for me? If samplers aren't available in opengl 3.1, why can I use glGenSamplers without a problem?

What can I do to provide backwards compatibility? I'm guessing my only option will be to set the texture parameters every time the texture is being used for rendering, if samplers aren't available?

Answer 1

There are two possibilities:

1. Your graphics card/driver supports ARB_sampler_objects, in this case it is unsurprising that the function is supported. Feel free to use it.
2. The function is present anyway. In this case, strange as it sounds, you are not allowed to use it.

Check whether glGetStringi(GL_EXTENSION, ...) returns the sampler objects extension at some index. Only functionality from extensions that the implementation advertizes as "supported" is allowed to be used.
If you find some functions despite no support, they might work anyway, but they might as well not. It's undefined.

Note that although you would normally expect the function being named glGenSamplersARB when it comes from an ARB extension, that is not the case here, since this is a "backwards extension" that provides selected functionality which is present identically in a later version on hardware which isn't able to provide the full functionality of that later version.

(About the error code, note comment by Brett Hale)