《Unity着色器圣经》3.2.2 | ShaderLab深度写入

目录索引

译文

深度写入这个命令控制了物体表面像素写入 Z 缓冲（深度缓冲）的这一过程。它允许我们忽略或写入物体与相机间的深度。深度写入有两个可以设置的值，分别是开启（On）和关闭（Off），默认值为开启。我们通常在处理透明度时（例如混合）会关闭深度写入。

• ZWrite Off 处理透明度时
• ZWrite On 默认值

为什么我们需要在处理透明度时禁用 Z 缓冲？主要是因为半透明像素叠加（深度冲突）的问题。当我们处理半透明物体时，GPU 通常不知道哪个物体位于另一个物体前面，因此当我们在场景中移动摄像机时，像素之间会产生奇怪的重叠效果。要解决这个问题，我们只需将深度写入命令设置为“关闭（Off）”，停用 Z 缓冲区即可：

Shader "InspectorPath/shaderName" 
{
    Properties { … } 
    SubShader 
    { 
        Tags { "Queue"="Transparent" "RenderType"="Transparent" } 
        Blend SrcAlpha OneMinusSrcAlpha 
        ZWrite Off 
    } 
}

深度冲突（Z-fighting）发生在两个或多个物体具有相同的深度时，导致 Z 缓冲中的值完全相同。

接着，当尝试在渲染管线末端渲染这些像素时，就会出现上图所示的这种效果。由于 Z 缓冲无法确定究竟哪个物体位于另一个物体的后面，就会产生这些闪烁的线条。线条的形状会根据摄像机的位置而改变。

想修复这个问题，我们只需要用命令关闭深度写入（ZWrite off）、禁用 Z 缓冲区即可。

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原文对照

This command controls the writing of the surface pixels of an object to the Z-Buffer, that is, it allows us to ignore or respect the depth distance between the camera and an object. ZWrite has two values, which are: On and Off, where “On” corresponds to its default value. We generally use this command when working with transparencies, e.g., when we activate the Blending options.

• ZWrite Off For transparency.
• ZWrite On Default value.

Why should we disable the Z-Buffer when working with transparencies? Mainly because of the translucent pixel overlay (Z-fighting). When we work with semi-transparent objects, it is common that the GPU does not know which object lies in front of another, producing an overlapping effect between pixels when we move the camera in the scene. To fix this problem, we must simply deactivate the Z-Buffer by turning the ZWrite command to “Off” as the following example shows:

Shader "InspectorPath/shaderName" 
{
    Properties { … } 
    SubShader 
    { 
        Tags { "Queue"="Transparent" "RenderType"="Transparent" } 
        Blend SrcAlpha OneMinusSrcAlpha 
        ZWrite Off 
    } 
}

The Z-fighting occurs when we have two or more objects at the same distance from the camera, causing identical values in the Z-Buffer.

This effect occurs when trying to render a pixel at the end of the rendering pipeline. Since the Z-Buffer cannot determine which element is behind the other, it produces flickering lines that change shape depending on the camera’s position.

To correct this issue, we simply need to disable the Z-Buffer using the “ZWrite off” command.