cube渲染

FYI：

https://github.com/mrdoob/three.js/blob/master/examples/webgl_materials_cubemap.html

https://threejs.org/examples/webgl_materials_cubemap.html

//图片命名方式

• px = left
• nx = right
• py = top
• ny = bottom
• pz = front
• nz = back