1/w坐标在gl_FragCoord中代表什么? [英] What does the 1/w coordinate stand for in gl_FragCoord?

问题描述

gl_FragCoord变量存储四个分量:(x，y，z， 1/w )

The gl_FragCoord variable stores four components: (x, y, z, 1/w)

什么是 w 坐标，为什么将其存储为 1/w ?

What is the w coordinate and why is it stored as 1/w?

推荐答案

在这方面，GLSL和OpenGL规范不必要地造成混淆. OpenGL规范更容易理解:gl_FragCoord存储窗口空间顶点位置的X，Y和Z分量. X，Y和Z值的计算方法与在计算窗口空间位置时所述的方法相同(尽管像素中心和左上角的原点可以修改X和Y值).规范的Coordinate Transforms部分对此进行了说明.

The GLSL and OpenGL specifications are needlessly confusing in this regard. The OpenGL spec is easier to understand: gl_FragCoord stores the X, Y, and Z components of the window-space vertex position. The X, Y, and Z values are calculated as described for computing the window-space position (though the pixel-center and upper-left origin can modify the X and Y values). This is described in the Coordinate Transforms section of the spec.

gl_FragCoord的W分量是(1/W _c )，其中W _c 是 clip-space 顶点位置.是来自顶点着色器的gl_Position.w.

The W component of gl_FragCoord is (1 / W_c), where W_c is the clip-space vertex position. It's gl_Position.w from your vertex shader.

保持W _c 唯一有用的目的是反向转换gl_FragCoord 返回剪辑空间位置.如该页面所示，这需要乘以W _c .但是，由于gl_FragCoord仅存储此值的倒数，因此现在需要除以gl_FragCoord.w.

The only useful purpose for keeping W_c around is to reverse-transform gl_FragCoord to get the clip-space position back. Which, as that page shows, requires multiplying by W_c. But since gl_FragCoord only stores the inverse of this value, it now requires dividing by gl_FragCoord.w.

因此，我们可以假设OpenGL以这种方式存储它，因为不允许OpenGL太有意义；)看，这是OpenGL规范的每个部分都必须有一点荒谬的规则. XYZ组件的意义太大，因此他们决定让它存储您实际想要的值的倒数.

Therefore, we can assume that OpenGL stores it this way because OpenGL isn't allowed to make too much sense ;) See, it's a rule that every part of the OpenGL specification must have something that's a bit nonsensical. The XYZ components made too much sense, so they decided to have it stores the inverse of the value you actually want.

好的，从技术上讲，这是3D Labs创建GLSL以来的历史产物.我敢肯定他们这样做是出于纯粹自私的硬件原因，但是我没有真正的证据.

OK, technically this is a historical artifact from the days when 3D Labs created GLSL. I'm sure they did it for purely selfish hardware reasons, but I have no real proof of that.

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