glsl/cs: Initialize gl_GlobalInvocationID in main()

We initialize gl_GlobalInvocationID based on the extension spec
formula:

    gl_GlobalInvocationID =
        gl_WorkGroupID * gl_WorkGroupSize + gl_LocalInvocationID

https://www.opengl.org/registry/specs/ARB/compute_shader.txt

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
3 files changed