gl_SamplePosition - contains the location of the current sample within the current fragment

       Copyright © 2011-2014 Khronos Group

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

       in vec2 gl_SamplePosition ;.SH "DESCRIPTION"

       gl_SamplePosition is a fragment language input variable that contains the location within a fragment of
       the sample currently being processed. The x and y components of gl_SamplePosition contain the sub-pixel
       coordinate of the current sample and will have values in the range 0.0 to 1.0. The sub-pixel coordinates
       of the center of the pixel are always (0.5, 0.5). Any static use of gl_SamplePosition causes the entire
       fragment shader to be evaluated per-sample rather than per-fragment. When rendering to a non-multisample
       buffer, or if multisample rasterization is disabled, gl_SamplePosition will be (0.5, 0.5).

       gl_SamplePosition - contains the location of the current sample within the current fragment

gl_SampleID(), gl_SampleMask(), gl_FragCoord()

       ┌───────────────────┬───────────────────────────────────────────────────────────────────────────────────┐
       │                   │        OpenGLShadingLanguageVersion                                            │
       ├───────────────────┼──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┤
       │ Function          │ 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_SamplePosition │  -   │  -   │  -   │  -   │  -   │  -   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │
       └───────────────────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┘