I have a user reporting this compile error:
Fragment shader uses varying gl_FrontFacing but vertex shader does not write to it.
…on this hardware (shiver):
Renderer: Intel Cantiga
Version: 2.0.0 - Build 184.108.40.2069
GLSL Version: 1.10 - Intel Build 220.127.116.119
…and this is the line that triggers the error:
if (!gl_FrontFacing) n.z = -n.z;
I found this statement in the ARB_fragment_shader spec:
The fragment shader has access to the read-only built-in variable gl_FrontFacing whose value is true if the fragment belongs to a front-facing primitive.
A driver bug, or am I missing something?