Portal:OpenGL Shading Language/Tessellation Evaluation Shader

The Tessellation Evaluation Shader (TES) is the shader stage responsible for computing the actual tessellated vertices. The fixed-function tessellator takes a patch and breaks it into pieces; the TES takes the patch data and decides how to interpolate it to generate the new per-vertex data for each of the smaller pieces of the original patch.

The TES acts similarly to a vertex shader, in that there is a 1:1 correlation between a vertex in the tessellated patch and a TES invocation. Thus, every TES is responsible for computing a given vertex in the tessellated patch.