The vertex shader is just a passthrough shader. It sends the vertex position along to the next stage without any modification.
The tessellation control shader begins by defining the number of vertices in the output patch:
layout (vertices = 4) out;
Note that this is not the same as the number of vertices that will be produced by the tessellation process. In this case, the patch is our four control points, so we use a value of four.
The main method within the TCS passes the input position (of the patch vertex) to the output position without modification. The gl_out and gl_in arrays contain the input and output information associated with each vertex in the patch. Note that we assign and read from gl_InvocationID in these ...
