在Shader修改Depth Value

In the coordinate systems tutorial we said that perspective division is performed after the vertex shader has run, dividing the gl_Position's xyz coordinates by its w component. We also know from the depth testing tutorial that the z component of the resulting division is equal to that vertex's depth value. Using this information we can set the z component of the output position equal to its w component which will result in a z component that is always equal to 1.0, because when the perspective division is applied its z component translates to w / w = 1.0:

void main()
{
    vec4 pos = projection * view * vec4(position, 1.0);
    gl_Position = pos.xyww;
    TexCoords = position;
}  

The resulting normalized device coordinates will then always have a z value equal to 1.0: the maximum depth value.

上面的意思就是，

v' = MVP * v

v'z / v'w = 深度值。就是这个顶点的深度值

所有，利用Unity试了下，是对的。

用Red cube和 Blue cube是了下。

无论Blue在什么地方，都是被挡着。

Shader "Unlit/Blue"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			// make fog work
			#pragma multi_compile_fog
			
			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2f
			{
				float2 uv : TEXCOORD0;
				UNITY_FOG_COORDS(1)
				float4 vertex : SV_POSITION;
			};

			sampler2D _MainTex;
			float4 _MainTex_ST;
			
			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
				o.vertex = o.vertex.xyww;
				o.uv = TRANSFORM_TEX(v.uv, _MainTex);
				return o;
			}
			
			fixed4 frag (v2f i) : SV_Target
			{
				// sample the texture
				fixed4 col = tex2D(_MainTex, i.uv);
				//return col;
				return fixed4(0, 0, 0.5, 1);
			}
			ENDCG
		}
	}
}

Shader "Unlit/Reg"
{
	Properties
	{
		_MainTex ("Texture", 2D) = "white" {}
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			// make fog work
			#pragma multi_compile_fog
			
			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2f
			{
				float2 uv : TEXCOORD0;
				UNITY_FOG_COORDS(1)
				float4 vertex : SV_POSITION;
			};

			sampler2D _MainTex;
			float4 _MainTex_ST;
			
			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
				o.uv = TRANSFORM_TEX(v.uv, _MainTex);
				
				return o;
			}
			
			fixed4 frag (v2f i) : SV_Target
			{
				// sample the texture
				fixed4 col = tex2D(_MainTex, i.uv);
				//return col;
				return fixed4(0.5, 0, 0, 1);
			}
			ENDCG
		}
	}
}