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

Tessellation Evaluation Shader Variables

Similar to tessellation control shaders, tessellation evaluation shaders have a gl_in array that is actually an array of structures, with each element defined as shown in Example 9.7.

Example 9.7. gl_in Parameters for Tessellation Evaluation Shaders

in gl_PerVertex {   vec4 gl_Position;   float gl_PointSize;   float gl_ClipDistance[]} gl_in[gl_PatchVerticesIn];

Additionally, the following scalar values, described in Table 9.4, are provided for determining which primitive and for computing the position of the output vertex.

Table 9.4. Tessellation Control Shader Input Variables

The output vertex’s data ...