Programatically determine if OpenGL function is supported by hardware

Question

I am very new to OpenGL so perhaps this is obvious, but is it possible to determine whether a specific function is supported by a given video card? This came up as I am using an old computer with an ATI Radeon 9550 video card, running Lubuntu 12.10 and discovered that it did not support the use of dFdx and dFfy. I was able to get around this problem but now I am curious if I can find out whether a failure has occurred due to a problem like this, and take action based on this, possibly using alternative methods and such.

Answer 1

You can check the supported OpenGL version using glGetString(GL_VERSION) or glGetInteverv(GL_MAJOR_VERSION, …); glGetInteverv(GL_MINOR_VERSION, …);. With OpenGL-3 and onwards, the OpenGL major version directly corresponds to hardware capabilites.

With older versions things are not as strict and due to OpenGL's abstract device model you can not really "query" hardware capabilities. You can check which extensions are supported, which is a good indicator for supported capabilities, as many ARB extensions made it into core functionality. If the extension on which a certain feature of a present OpenGL version is based, is not being supported then the core feature will be emulated, probably.

I know it's very vague and shaky, but that's how it is. The only other option is keeping around a database of GL_RENDERER strings and match against that.

Answer 2

Generally speaking, you cannot. Not for the kind of thing you're talking about.

dFdx and dFdy have been part of GLSL since version 1.10 (the first version in core OpenGL 2.0). Support for them is not optional.

Your problem is that ATI/AMD wants to claim that their older card supports 2.x, but their hardware can't actually do all the things that 2.x requires. So they lie about it, claiming support while silently making these null operations.

OpenGL doesn't have a way to detect perfidy. The only thing you can do is keep around a list of cards and use the GL_VENDOR and GL_RENDERER strings to test against.