gl_PrimitiveIDIn — contains the index of the current primitive
in int gl_PrimitiveIDIn ;
      
            gl_PrimitiveIDIn is a geometry language input variable that holds
            the number of primitives processed by the shader since the current set of rendering
            primitives was started. The first primitive processed by the drawing command is numbered
            zero and the primitive ID counter is incremented after every individual point, line
            or triangle primitive is processed. For triangles drawn in point or line mode, the
            primitive ID counter is incremented only once, even through multiple points or lines
            may actually be drawn. Restarting a primitive topology using the primitive restart
            index has no effect on the primitive ID counter.
        
| OpenGL Shading Language Version | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Variable Name | 1.10 | 1.20 | 1.30 | 1.40 | 1.50 | 3.30 | 4.00 | 4.10 | 4.20 | 4.30 | 4.40 | 4.50 | 
| gl_PrimitiveIDIn | - | - | - | - | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | 
Copyright © 2011-2014 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.