One of our testers updated his ATI driver, and our fragment shader stopped working as expected. I updated my driver, and found the issue: gl_FrontFacing doesn't seem to be set to any meaninful value, i.e. testing
both return true.
We're using an old version of GLSL. Our shaders are prefaced with:
The details of this video card:
Driver Packaging Version 8.831.2-110308a-115928C-ATI
Catalyst Version 11.3
Graphics Chipset ATI Radeon HD 4850