title: mering same geometry with different ambient colors
body: <p>I create a custom geometry and use MeshPhongMaterial as material. Because my geometry is large, so I want to merge them in to one geometry for better performance. Problem is that i want to use different ambient color to each child geometry. I think I can change color by using more material and change materialIndex for each face, but it maybe not work and may costs a lot of time and use more texture. Is there any simple way to archive this? I'm not sure about how three.js render with different material so i have no idea for this.Thanks for you help.</p>