Shader "Custom/Luminance"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        //材质上加个复选框
        [Toggle(UNITY_UI_LUMINANCE)]
        _Luminance ("Luminance", Float) = 0

        //支持 UGUI ScrollRect 遮罩
        _StencilComp ("Stencil Comparison", Float) = 8
        _Stencil ("Stencil ID", Float) = 0
        _StencilOp ("Stencil Operation", Float) = 0
        _StencilWriteMask ("Stencil Write Mask", Float) = 255
        _StencilReadMask ("Stencil Read Mask", Float) = 255
        _ColorMask ("Color Mask", Float) = 15
        //END
    }
    SubShader
    {
        Tags { "RenderType"="Transparent" "Queue" = "Transparent" "IgnoreProjector" = "True" "PreviewType" = "Plane" }
        LOD 100

        //支持 UGUI ScrollRect 遮罩
        Stencil
        {
            Ref [_Stencil]
            Comp [_StencilComp]
            Pass [_StencilOp] 
            ReadMask [_StencilReadMask]
            WriteMask [_StencilWriteMask]
        }
        ColorMask [_ColorMask]
        //END

        //Alpha混合
        Blend SrcAlpha OneMinusSrcAlpha

        Pass
        {
            CGPROGRAM
            #pragma target 3.0 //DX9 着色器模型 3.0
            #pragma vertex vert
            #pragma fragment frag
            //生成多版本shader
            #pragma multi_compile __ UNITY_UI_LUMINANCE

            #include "UnityCG.cginc"

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

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            float _Luminance;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);

                #ifdef UNITY_UI_LUMINANCE
                col.rgb = Luminance(col.rgb);
                #endif

                return col;
            }
            ENDCG
        }
    }
}