Hello. I want to use Quad for primitives of all objects. Why OpenGL ES does not support Quad?
The OpenGL ES 1.0 Spec reveals the answer in Section 2.6:
Quads and polygons are eliminated since they can be readily emulated with triangles and it reduces an ambiguity with respect to decomposition of these primitives to triangles, since it is entirely left to the application. Elimination of quads and polygons removes special cases for line mode drawing requiring edge flags (should PolygonMode be re-instated).