Unity3d Overlay Shader

Shader "Custom/Overlay" {

    Properties {

        _OverlayTex ("Overlay (RGB)", 2D) = "white" {}

    }



    SubShader {

        Tags { "RenderType"="Transparent" "Queue"="Transparent+1000"}

        LOD 200



        GrabPass {}



        Pass {

            CGPROGRAM
// Upgrade NOTE: excluded shader from DX11 and Xbox360; has structs without semantics (struct v2f members projPos)
#pragma exclude_renderers d3d11 xbox360



            #pragma vertex vert

            #pragma fragment frag



            #include "UnityCG.cginc"



            sampler2D _GrabTexture;

            sampler2D _OverlayTex;



            struct appdata_t {

                float4 vertex : POSITION;

                float4 texcoord : TEXCOORD0;

            };



            struct v2f {

                float4 vertex : POSITION;

                float2 uv : TEXCOORD0;

                float4 projPos : TEXCOORD1;

            };



            float4 _OverlayTex_ST;



            v2f vert( appdata_t v ){

                v2f o;

                o.vertex = mul( UNITY_MATRIX_MVP, v.vertex );

                o.uv = TRANSFORM_TEX( v.texcoord, _OverlayTex );

                o.projPos = ComputeGrabScreenPos( o.vertex );

                return o;

            }



            half4 frag( v2f i ) : COLOR {

                i.projPos /= i.projPos.w;

                half4 base = tex2D( _GrabTexture, float2( i.projPos.xy ));

                half4 overlay = tex2D( _OverlayTex, i.uv );



                return lerp(   1 - 2 * (1 - base) * (1 - overlay),    2 * base * overlay,    step( base, 0.5 ));

            }



            ENDCG

        }

    }

}