layout(triangles, equal_spacing, ccw) in;
in vec4 pos_es_in[];
out vec4 pos_fs_in;
// expects: interpolate
void main()
{
  pos_fs_in = interpolate(gl_TessCoord,pos_es_in[0], pos_es_in[1], pos_es_in[2]);
  gl_Position = pos_fs_in;
}