gl_InstanceID - contains the index of the current primitive in an instanced draw command

       Copyright © 2011-2014 Khronos Group

[FIXME: source]                                    11/18/2024                                  GL_INSTANCEID(3G)

       in int gl_InstanceID ;.SH "DESCRIPTION"

       gl_InstanceID is a vertex language input variable that holds the integer index of the current primitive
       in an instanced draw command such as glDrawArraysInstanced. If the current primitive does not originate
       from an instanced draw command, the value of gl_InstanceID is zero.

       gl_InstanceID - contains the index of the current primitive in an instanced draw command

gl_VertexID()

       ┌───────────────┬───────────────────────────────────────────────────────────────────────────────────┐
       │               │        OpenGLShadingLanguageVersion                                            │
       ├───────────────┼──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┤
       │ Variable      │ 1.10 │ 1.20 │ 1.30 │ 1.40 │ 1.50 │ 3.30 │ 4.00 │ 4.10 │ 4.20 │ 4.30 │ 4.40 │ 4.50 │
       │ Name          │      │      │      │      │      │      │      │      │      │      │      │      │
       ├───────────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┤
       │ gl_InstanceID │  -   │  -   │  -   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │
       └───────────────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┘