Shader "Custom/ImageMask"
{  
    Properties 
    {  
        [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
        _Mask ("Base (RGB)", 2D) = "white" {}  
        _Color ("Tint", Color) = (1,1,1,1)
        _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
        [Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip ("Use Alpha Clip", Float) = 0
    }


    SubShader 
    {
        Tags
        { 
            "Queue"="Transparent"  "IgnoreProjector"="True" "RenderType"="Transparent" "PreviewType"="Plane" "CanUseSpriteAtlas"="True"
        }

        Stencil
        {
            Ref [_Stencil]
            Comp [_StencilComp]
            Pass [_StencilOp] 
            ReadMask [_StencilReadMask]
            WriteMask [_StencilWriteMask]
        }


        Cull Off
        Lighting Off
        ZWrite Off
        ZTest [unity_GUIZTestMode]
        Blend SrcAlpha OneMinusSrcAlpha
        ColorMask [_ColorMask]


        Pass
        {         
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag


            #include "UnityCG.cginc"
            #include "UnityUI.cginc"


            #pragma multi_compile __ UNITY_UI_ALPHACLIP


            struct a2v
            {
                fixed2 uv : TEXCOORD0;
                half4 vertex : POSITION;
                float4 color    : COLOR;
            };


            fixed4 _Color;


            struct v2f
            {
                fixed2 uv : TEXCOORD0;
                half4 vertex : SV_POSITION;
                float4 color    : COLOR;
            };


            sampler2D _MainTex;
            sampler2D _Mask;  


            v2f vert (a2v i)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(i.vertex);
                o.uv = i.uv;


                o.color = i.color * _Color;
                return o;
            }


            fixed4 frag (v2f i) : COLOR
            {
                half4 color = tex2D(_MainTex, i.uv) * i.color; 
                half4 mask = tex2D(_Mask, i.uv); 
                color.a *= mask.a;
                return color;
            }
            ENDCG
        }  
    }   
}