Hi,
i just ran into the same problem described here:
http://www.opengl.org/discussion_boards/ubbthreads.php?ubb=showflat&Number=286118
I am trying to use the gl_PrimitiveID variable to access a texture buffer in the tessellation control shader and the compiler complains that the variable is not defined and i should enable the EXT_gpu_shader_4 extension:
error C7531: global variable gl_PrimitiveID requires "#extension GL_EXT_gpu_shader4 : enable" before use
This is on a OpenGL 4.1 core context in a version 410 tessellation control shader. I am using a GTX 480 on ForceWare 260.93 (also tried 261.00 and 262.99).
This just stopped me cold here.
Just some shader snippets to illustrate the problem:
#version 410 core
// input/output definitions ///////////////////////////////////////////////////////////////////////
in per_vertex {
smooth vec2 texcoord;
} vertex_in[];
out per_vertex {
smooth vec2 texcoord;
} vertex_out[];
// uniform input definitions //////////////////////////////////////////////////////////////////////
uniform samplerBuffer edge_densities;
// output layout definitions //////////////////////////////////////////////////////////////////////
layout(vertices = 3) out;
[...]
vec4 tess_outer = texelFetch(edge_densities, gl_PrimitiveID * 2);
vec4 tess_inner = texelFetch(edge_densities, gl_PrimitiveID * 2 + 1);
gl_TessLevelOuter[0] = tess_outer.x;
gl_TessLevelOuter[1] = tess_outer.y;
gl_TessLevelOuter[2] = tess_outer.z;
gl_TessLevelInner[0] = tess_inner.x;
gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
-chris