请问几个DirectX的有关问题

请教几个DirectX的问题
1：切线贴图就是法线贴图的意思么？
如果不是，那两者有什么区别？

2：The NPatch mode segments 是什么意思？
原文：
The NPatch mode segments The NPatch mode segments from IDirect3DDevice9::SetNPatchMode

3：如下语句是什么意思：
The source primitive is used as a light map that scales the contents of the frame buffer to 

darken it when appropriate 

如果要看上下文，参阅下面的内容

Another application of alpha blending is to control the lighting in a 3D scene, also called 

light mapping. Setting the source blend state to D3DBLEND_ZERO and the destination blend 

state to D3DBLEND_SRCALPHA darkens a scene according to the source alpha information. The 

source primitive is used as a light map that scales the contents of the frame buffer to 

darken it when appropriate. This produces monochrome light mapping.




------解决方案--------------------
没听说过切线贴图 只听说过法线贴图