opengl es 1.1：如何将多个材质应用于单个对象？

Question

I've a simple cube which i have imported from Blender 3D; this cube has 3 different materials for its face; yellow, pink and blue.

So far i have managed to apply one material on an opengl es cube. However i am wondering how to apply several materials to the same cube. As you will see from the OBJ file; the materials share the same vertices; only their indices change. First thought has been to use a drawelement for each of this material; but is it first really working ? and how performance costly is it and is there a better approach in Openg GL ES 1.1 ?

Many thanks for any pointer you can provide me.

Cheers, Stéphane

# Blender v2.61 (sub 0) OBJ File: ''
# www.blender.org
mtllib MultiColorCube.mtl
o Cube
v 1.000000 -1.000000 -1.000000
v 1.000000 -1.000000 1.000000
v -1.000000 -1.000000 1.000000
v -1.000000 -1.000000 -1.000000
v 1.000000 1.000000 -0.999999
v 0.999999 1.000000 1.000001
v -1.000000 1.000000 1.000000
v -1.000000 1.000000 -1.000000
v -1.000000 1.000000 1.000000
v 0.999999 1.000000 1.000001
v -1.000000 -1.000000 1.000000
v 1.000000 -1.000000 1.000000
v 1.000000 -1.000000 -1.000000
v 1.000000 -1.000000 -1.000000
v -1.000000 -1.000000 -1.000000
v -1.000000 -1.000000 -1.000000
v -1.000000 -1.000000 1.000000
v -1.000000 1.000000 -1.000000
v -1.000000 1.000000 -1.000000
v -1.000000 1.000000 1.000000
v 1.000000 1.000000 -0.999999
v 1.000000 1.000000 -0.999999
v 0.999999 1.000000 1.000001
v 1.000000 -1.000000 1.000000
vn 0.000000 -1.000000 0.000000
vn 0.000000 1.000000 0.000000
vn -1.000000 -0.000000 -0.000000
vn 0.000000 0.000000 -1.000000
vn 0.000000 0.000000 1.000000
vn 0.000000 0.000000 0.999969
vn 1.000000 0.000000 0.000000
usemtl bleu
s off
f 1//1 2//1 3//1 4//1
f 5//2 8//2 7//2 6//2
f 17//3 20//3 19//3 16//3
f 21//4 14//4 15//4 18//4
usemtl Jaune
s 1
f 10//5 9//5 11//6
f 12//5 10//5 11//6
usemtl Pink
s off
f 13//7 22//7 23//7 24//7

Answer 1

Yes, it is possible to change material state settings in between the glDrawElements calls. You can just set color for first chunk of indices, then call glDrawElements with these indices, then set next color and so on. Performancewise it is usually best to draw geometry in as large chunks as possible and change material settings as rarely as possible. So, assuming all you change is the color, then having colors as vertex attributes may be better, eventhough it uses up more memory for the vertex buffer. But as long as your material change is nothing more than a glColor call, you should be fine. For more detailed performance advices you need to describe in more detail what you're actually rendering.