通道遮罩 ColorMask可以让我们制定渲染结果的输出通道，而不是通常情况下的RGBA这4个通道全部写入。可选参数是 RGBA 的任意组合以及 0， 这将意味着不会写入到任何通道，可以用来单独做一次Z测试，而不将结果写入颜色通道

Shader "DepthMask" {

    SubShader {
        // Render the mask after regular geometry, but before masked geometry and
        // transparent things.

        Tags {"Queue" = "Geometry-10" }

        // Turn off lighting, because it's expensive and the thing is supposed to be
        // invisible anyway.

        Lighting Off

        // Draw into the depth buffer in the usual way.  This is probably the default,
        // but it doesn't hurt to be explicit.

        ZTest LEqual
        ZWrite On

        // Don't draw anything into the RGBA channels. This is an undocumented
        // argument to ColorMask which lets us avoid writing to anything except
        // the depth buffer.

        ColorMask 0

        // Do nothing specific in the pass:

        Pass {}
    }
}

实现如图效果，前面的cube改为DepthMask的shader，实现在前面的cube透明，但是仍然挡住了后面cube的效果

fdd904b67e934e24b10e5c9c84392fc2[1].jpg