unity-shader stencil（模板测试）的基本应用

先看效果，后上代码，最后解释：
（1）使用stencil，控制球体显示在墙体Cube上：scene中位置排序：相机->墙体Cube->球体->背景BG
（2）在game中的效果：球体->墙体Cube->背景BG

Shader "Unlit/stencil_BG01"
{
     
    Properties
    {
     
        _MainTex ("Texture", 2D) = "white" {
     }
        _refVal("Stencil ref value",int)=0
    }
    SubShader
    {
     
        Tags {
     "Queue"="Geometry+1" "RenderType"="Opaque" }
        LOD 100

        Pass
        {
     
            Tags{
      "LightModel"="OnForwardBase" }
            //ZWrite Off  
            ZTest Always
            Stencil{
     
                Ref[_refVal]
                Comp Always //默认为 Always
                Pass Replace
                Fail Replace
            }
            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 = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
     
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);
                return col;
            }
            ENDCG
        }
    }
}

Shader "Unlit/stencil_Sphere02"
{
     
    Properties
    {
     
        _MainTex ("Texture", 2D) = "white" {
     }
        _refVal("Stencil ref value",int)=10
    }
    SubShader
    {
     
        Tags {
     "Queue"="Geometry+2" "RenderType"="Opaque" }
        LOD 100

        Pass
        {
     
            Tags{
      "LightModel"="ForwardBase" }
            ZTest Always
            //ColorMask rgb //0代表不输出任何颜色
            Stencil
            {
     
                Ref[_refVal]
                Comp GEqual 
                Pass Replace                
            }
            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 = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
     
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);
                return col;
            }
            ENDCG
        }
    }
}

Shader "Unlit/stencil_Cube03"
{
     
    Properties
    {
     
        _MainTex ("Texture", 2D) = "white" {
     }
        _refVal("Stencil ref value",int)=5
    }
    SubShader
    {
     
        Tags {
     "Queue"="Geometry+3" "RenderType"="Opaque" }
        LOD 100

        Pass
        {
     
            Tags{
     "LightModel"="ForwardBase" }
            //ZWrite Off  
            ZTest Always
            
            Stencil
            {
     
                Ref[_refVal]
                Comp GEqual 
                Pass Replace                
            }
            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 = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                UNITY_TRANSFER_FOG(o,o.vertex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
     
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                // apply fog
                UNITY_APPLY_FOG(i.fogCoord, col);
                return col;
            }
            ENDCG
        }
    }
}

上面三个shader对应3个物体
（3）下面来解释下stencil命令：


最核心的理解就下面这几句：
Stencil
{
Ref[_refVal]
Comp GEqual
Pass Replace
}
Ref[_refVal]： 将_refVal 和Stencil中的值比较，Stencil缓存中默认为0
Comp GEqual : 比较条件是“大于等于”
Pass Replace：符合比较条件的执行“Replace”操作
以上的效果，也可以通过控制渲染顺序实现，这里不再多说，多动手多思考，FrameDebug是个好东西！！