OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Geometry Shader Outputs

The output of the geometry shader is fed into the primitive setup engine, rasterizer, and eventually into the fragment shader. In general, the output of the geometry shader is equivalent to the output of the vertex shader if no geometry shader is present. As many of the same outputs exist in the geometry shader as exist in the vertex shader. The same gl_PerVertex interface block specification is used for per-vertex outputs in the geometry shader. The definition of this block is given in Example 10.4.

Example 10.4. Implicit Declaration of Geometry Shader Outputs

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out gl_PerVertex{    vec4    gl_Position;    float   gl_PointSize;    float   gl_ClipDistance[];};

Note that although the same gl_PerVertex ...