gl_SampleID - contains the index of the sample currently being processed

       Copyright © 2011-2014 Khronos Group

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

       in int gl_SampleID ;.SH "DESCRIPTION"

       gl_SampleID is a fragment language input variable that contains the index of the sample currently being
       processed. This variable is in the range 0 to gl_NumSamples() - 1, where gl_NumSamples() is the total
       number of samples in each fragment for the current framebuffer (and thus 1 if rendering to a
       non-multisample buffer). Any static use of this variable in a fragment shader causes the entire shader to
       be evaluated per-sample rather than per-fragment.

       When rendering to a non-multisample buffer, or if multisample rasterization is disabled, gl_SampleID will
       always be zero.  gl_NumSamples() is the sample count of the framebuffer regardless of whether multisample
       rasterization is enabled or not.

       gl_SampleID - contains the index of the sample currently being processed

gl_SamplePosition(), gl_NumSamples()

       ┌─────────────┬───────────────────────────────────────────────────────────────────────────────────┐
       │             │        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_SampleID │  -   │  -   │  -   │  -   │  -   │  -   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │
       └─────────────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┘