Shader "BF/PostEffect/VividBloom"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }

    CGINCLUDE
    #include "UnityCG.cginc"

    sampler2D _MainTex, _SourceTex;
    float4 _MainTex_TexelSize;

    half4 _Filter;

    half _Intensity;

    struct VertexData
    {
        float4 vertex : POSITION;
        float2 uv : TEXCOORD0;
    };

    struct Interpolators
    {
        float4 pos : SV_POSITION;
        float2 uv : TEXCOORD0;
    };

    Interpolators VertexProgram (VertexData v)
    {
        Interpolators i;
        i.pos = UnityObjectToClipPos(v.vertex);
        i.uv = v.uv;
        return i;
    }

    half3 Sample (float2 uv)
    {
        return tex2D(_MainTex, uv).rgb;
    }

    half3 SampleBox (float2 uv, float delta)
    {
        float4 o = _MainTex_TexelSize.xyxy * float2(-delta, delta).xxyy;
        half3 s =
        Sample(uv + o.xy) + Sample(uv + o.zy) +
        Sample(uv + o.xw) + Sample(uv + o.zw);
        return s * 0.25f;
    }

    half3 Prefilter (half3 c)
    {
        half brightness = max(c.r, max(c.g, c.b));
        half soft = brightness - _Filter.y;
        soft = clamp(soft, 0, _Filter.z);
        soft = soft * soft * _Filter.w;
        half contribution = max(soft, brightness - _Filter.x);
        contribution /= max(brightness, 0.00001);
        return c * contribution;
    }

    ENDCG

    SubShader
    {
        Cull Off
        ZTest Always
        ZWrite Off

        Pass
        { // 0
            CGPROGRAM
            #pragma vertex VertexProgram
            #pragma fragment FragmentProgram

            half4 FragmentProgram (Interpolators i) : SV_Target
            {
                return half4(Prefilter(SampleBox(i.uv, 1)), 1);
            }
            ENDCG
        }

        Pass
        { // 1
            CGPROGRAM
            #pragma vertex VertexProgram
            #pragma fragment FragmentProgram

            half4 FragmentProgram (Interpolators i) : SV_Target
            {
                return half4(SampleBox(i.uv, 1), 1);
            }
            ENDCG
        }

        Pass
        { // 2
            Blend One One

            CGPROGRAM
            #pragma vertex VertexProgram
            #pragma fragment FragmentProgram

            half4 FragmentProgram (Interpolators i) : SV_Target
            {
                return half4(SampleBox(i.uv, 0.5), 1);
            }
            ENDCG
        }

        Pass { // 3
            CGPROGRAM
            #pragma vertex VertexProgram
            #pragma fragment FragmentProgram

            half4 FragmentProgram (Interpolators i) : SV_Target
            {
                half4 c = tex2D(_SourceTex, i.uv);
                c.rgb += _Intensity * SampleBox(i.uv, 0.5);
                return c;
            }
            ENDCG
        }

        Pass { // 4
            CGPROGRAM
            #pragma vertex VertexProgram
            #pragma fragment FragmentProgram

            half4 FragmentProgram (Interpolators i) : SV_Target
            {
                return half4(_Intensity * SampleBox(i.uv, 0.5), 1);
            }
            ENDCG
        }
    }
}