在 OpenGL 顶点着色器中，w 是什么，为什么要除以它? [英] In OpenGL vertex shaders, what is w, and why do I divide by it?

问题描述

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

  gl_FrontColor = gl_Color;

  vec3 ndc = clipCoord.xyz / clipCoord.w;

所以 clipCoord 只是做标准的固定管道转换.为什么我要除以 w，我从中得到什么?

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

推荐答案

W 是三维顶点的第四个坐标；这个顶点称为齐次顶点坐标.

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

简而言之，W 分量是划分其他向量分量的因子.当 W 为 1.0 时，齐次顶点坐标被标准化".要比较两个顶点，您应该将 W 值归一化为 1.0.

In few words, the W component is a factor which divides 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.

想想顶点 (1,1,1,1).现在增加 W 值(w > 1.0).标准化位置正在缩放！它会到达原点.想想顶点 (1,1,1,1).现在减小 W 值(W <1.0).归一化后的位置会无限大.

Think of 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 of the vertex (1,1,1,1). Now decrease the W value (W < 1.0). The normalized position is going to an infinite point.

除了缩放顶点坐标之外，W 坐标也是必需的，因为您必须将 4x4 矩阵(模型视图和/或投影矩阵)与 4x1 矩阵(顶点)相乘.

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).

当然，红皮书是明确的指南:

Of course, the Red Book is the definite guide:

红皮书附录

这篇关于在 OpenGL 顶点着色器中，w 是什么，为什么要除以它?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！