在OpenGL顶点着色中，w是什么，为什么要除以它?

void main(void)
{
  vec4 clipCoord = glModelViewProjectionmatrix * gl_Vertex;
  gl_Position = clipCoord;

  gl_FrontColor = gl_Color;

  vec3 ndc = clipCoord.xyz / clipCoord.w;

So the clipCoord is just doing standard fixed pipeline transforms. Why do I divide by w, and what do I get from this?

所以clipCoord只是在做标准的固定管道变换。为什么要除以w，从这里得到什么?

1 个解决方案

#1

W is the fourth coordinate of a three dimensional vertex; This vertex is called homogeneous vertex coordinate.

W是三维顶点的第四个坐标;这个顶点称为齐次顶点坐标。

In few words, the W component is a factor wich divide the other vector components. When W is 1.0, the homogeneous vertex coordinates are "normalized". To compare two vertices, you should normalize the W value to 1.0.

简而言之，W分量是一个分解其他向量分量的因子。当W为1.0时，齐次顶点坐标是“标准化的”。要比较两个顶点，应该将W值规范化为1.0。

Think to the vertex (1,1,1,1). Now increase the W value (w > 1.0). The normalized position is scaling! and it is going to the origin. Think to the vertex (1,1,1,1). Now decrease the W value (W < 1.0). The normalized position is going to an infinite point.

考虑顶点(1,1,1,1)现在增加W值(W > 1.0)。标准化的位置是缩放!它会到原点。考虑顶点(1,1,1,1)现在降低W值(W < 1.0)。归一化的位置是无限的。

Apart from scaling vertex coordinates, the W coordinate is necessary since you have to multiply a 4x4 matrix (the model view and/or the projection matrices) with a 4x1 matrix (the vertex).

除了缩放顶点坐标之外，W坐标是必要的，因为你必须用一个4x1矩阵(顶点)乘以4x4矩阵(模型视图和/或投影矩阵)。

Of course, the Red Book is the definite guide:

当然，红皮书是明确的指南:

Red Book Appendix

红书附录

#1