Shader "Custom/DistortionSurfaceShader" {
    Properties {
        _MainTex ("Tint Color (RGB)", 2D) = "white" {}
        _BumpAmt  ("Distortion", range (0,128)) = 10
        _BumpMap ("Normalmap", 2D) = "bump" {}
        _Color ("Color", Color) = (1,1,1,1)
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
    }
    SubShader {

        GrabPass {}

        Cull Off


        Tags { "Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Opaque" }
        LOD 200

        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all light types
        #pragma surface surf Standard fullforwardshadows

        // Use shader model 3.0 target, to get nicer looking lighting
        #pragma target 3.0

        sampler2D _MainTex;
        sampler2D _BumpMap;
        sampler2D _GrabTexture;

        float4 _GrabTexture_TexelSize;

        float _BumpAmt;

        struct Input {
            float2 uv_MainTex;
            float2 uv_BumpMap;
            float4 screenPos;
        };

        half _Glossiness;
        half _Metallic;
        fixed4 _Color;

        // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
        // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
        // #pragma instancing_options assumeuniformscaling
        UNITY_INSTANCING_BUFFER_START(Props)
            // put more per-instance properties here
        UNITY_INSTANCING_BUFFER_END(Props)

        void surf (Input IN, inout SurfaceOutputStandard o) {
            float2 screenUV = IN.screenPos.xy / IN.screenPos.w;
            fixed3 nor = _BumpAmt * UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));
            float2 offset = nor.rg * _GrabTexture_TexelSize.xy;
            half4 col = tex2D( _GrabTexture, screenUV + offset);

            half4 tex = tex2D(_MainTex, IN.uv_MainTex);
            o.Albedo = tex.rgb * _Color.rgb * col.rgb;
            o.Normal = nor;
            o.Alpha = tex.a * _Color.a;

            // Metallic and smoothness come from slider variables
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
        }
        ENDCG
    }
    //FallBack "Diffuse"
}