Shader "Custom/Overlay"
 {
     Properties
     {
         _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
     }
     SubShader
     {
         Tags {"Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent"}
         ZWrite Off Lighting Off Cull Off Fog { Mode Off } Blend DstColor SrcColor
         LOD 110
         Pass
         {
             CGPROGRAM
             #pragma vertex vert_vct
             #pragma fragment frag_mult
             #pragma fragmentoption ARB_precision_hint_fastest
             #include "UnityCG.cginc"
             static const float4 _StartColor = float4(0.5f,0.5f,0.5f,0.5f);
             sampler2D _MainTex;
             struct vin_vct
             {
                 float4 vertex : POSITION;
                 float4 color : COLOR;
                 float2 texcoord : TEXCOORD0;
             };
             struct v2f_vct
             {
                 float4 vertex : POSITION;
                 fixed4 color : COLOR;
                 half2 texcoord : TEXCOORD0;
             };

             v2f_vct vert_vct(vin_vct v)
             {
                 v2f_vct o;
                 o.vertex = UnityObjectToClipPos(v.vertex);
                 o.color = v.color;
                 o.texcoord = v.texcoord;
                 return o;
             }
             float3 overlay_value(float3 b, float3 o)
             {
                float3 over;
                float f = 1.0-(1.0-b)*(1.0-o);
                float g =  b * o;
                if(b.r<0.5)
                    over.r = g;
                else
                    over.r = f;
                if(b.g<0.5)
                    over.g = g;
                else
                    over.g = f;
                if(b.b<0.5)
                    over.b = g;
                else
                    over.b = f;
                return over;
             }
             float4 frag_mult(v2f_vct i) : COLOR
             {
                 float4 tex = tex2D(_MainTex, i.texcoord);
                 float4 final;
                 final.rgb = overlay_value(tex.rgb,i.color.rgb);
                 final.a = i.color.a * tex.a;
                 return lerp(_StartColor, final, final.a);
             }
             ENDCG
        }
    }
}