Shader "Unlit/BlackAreaBlit"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _MaskTex ("Mask Texture", 2D) = "white" {}
    }
    SubShader
    {
        Tags { 
            "RenderType" = "Opaque"
            "RenderPipeline" = "UniversalPipeline"
        }
        LOD 100

        Pass
        {
            ZTest Off
            ZWrite Off
            Cull Off
            
            CGPROGRAM
            #pragma target 2.0
            #pragma vertex vert
            #pragma fragment frag

            #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;

            sampler2D _MaskTex;
            float4 _MaskTex_ST;

            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
            {
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                fixed4 mask = tex2D(_MaskTex, i.uv);
                fixed4 black = fixed4(0, 0, 0, 1);
                float minAlpha = 0.02;
                if (mask.r > minAlpha)
                {
                    float scale = mask.r * 1;
                    scale = min(scale, 1);
                    scale = max(scale, minAlpha);
                    return col * scale;
                }
                return col * minAlpha;
            }
            ENDCG
        }
    }
}