When the tessellation shaders are active, we can only render one kind of primitive: the patch (GL_PATCHES). Rendering any other kind of primitive (such as triangles, or lines) while a tessellation shader is active is an error. The patch primitive is an arbitrary chunk of geometry (or any information) that is completely defined by the programmer. It has no geometric interpretation beyond how it is interpreted within the TCS and TES. The number of vertices within the patch primitive is also configurable. The maximum number of vertices per patch is implementation-dependent, and can be queried via the following command:
glGetIntegerv(GL_MAX_PATCH_VERTICES, &maxVerts);
We can define the number of vertices per patch with ...
