DirectX数学函数混淆

问题描述

在我浏览一些旧的DirectX代码时，我来自函数D3DXVec3Transform和D3DXVec3TransformCoord。在查找他们的描述时，他们看起来很相似，但我看不出两者之间的区别。有人可以解释D3DXVec3Transform和D3DXVec3TransformCoord之间的区别是什么，以及它们的数学？

解决方案

3D向量通过矩阵得到其中w = 1的4D向量。3D向量可以被描述为其中w = 1的4D向量。

D3DXVec3Transform返回4D向量，其中w！= 1。
D3DXVec3TransformCoord得到的4D矢量和项目到w = 1，使其成为3D矢量。

编辑：这里是我google'd的文件发现如果有兴趣如何做转型：

While I was going over some older DirectX code, I came by the functions D3DXVec3Transform and D3DXVec3TransformCoord. Upon looking up the descriptions for them, they seemed rather similar but I don't see what the difference between the two are. Can someone please explain what is the difference between D3DXVec3Transform and D3DXVec3TransformCoord are, along with the math behind them?

解决方案

When you transform a 3D vector by matrix it results in a 4D vector where w!=1

a 3D vector can be described as 4D vector where w=1.

D3DXVec3Transform returns the 4D vector where w!=1.D3DXVec3TransformCoord gets the 4D vector and the projects it onto w=1 to make it 3D vector.

EDIT: And here is the paper I google'd and found if interested in how to do the transformation:http://www.heldermann-verlag.de/jgg/jgg01_05/jgg0404.pdf

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