shader里面經常看到normal向量是用WorldInverseTranspose矩陣做變換的，有時候也可以用WorldMatrix變換。

原理：

If your object is only ever rotated and translated, you can transform normals using the top left 3x3 portion of the world matrix.

If it is rotated, translated, and uniform scaled, you can do that same 3x3 matrix transform, but must then re-normalize the output vector to remove the scaling.

But if the transform includes a non uniform scale, shear, taper, etc, normals would no longer be correct after just a rotation. To get the right normals in such situations, you must transform them by the inverse transpose of the world matrix, then re-normalize the output vector.

The math is derived here: http://explodedbrain.livejournal.com/112906.html

Some shaders do this the complex slow way in order to be as robust as possible. Others figure that nobody in their right mind would ever use a non-uniform scale in a game, so they don't bother to support that, which simplifies the shader and makes rendering more efficient (but can lead to confusion if anyone ever does use an unsupported transform and gets bogus lighting results).

總結： 如果object沒有涉及到x,y,z方向的不統一縮放，就可以直接用WorldMatrix，否則用WorldInverseTranspose.

詳細介紹參考：http://www.arcsynthesis.org/gltut/Illumination/Tut09%20Normal%20Transformation.html

轉載于:https://www.cnblogs.com/smartgloble/p/3178559.html

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