Crepuscular Rays

// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'


Shader "Lighting/Crepuscular Rays" {

    Properties{
        _MainTex("Base (RGB)", 2D) = "white" {}
        _BlurTex("BlurTex (RGB)", 2D) = "white" {}
        _NumSamples("Number of Samples", Range(0, 1024)) = 128
        _Density("Density", Range(0, 1)) = 1.0
        _Weight("Weight", Range(0, 2)) = 1.0
        _Decay("Decay", Range(0, 1)) = 1.0
        _Exposure("Exposure", Range(0, 1)) = 1.0
        _Parameter("Kernel Offset", Range(0, 4)) = 1.0
        _Contrast("Contrast", Range(1, 5)) = 1.0
        _PerpendicularFalloff("Perpendicular Falloff Rate", Range(0.01, 1)) = 1.0
        _CosAngle("Angle", Float) = 1
        [IntRange] _StencilRef ("Stencil Ref", Range(0,255)) = 0
        _TintColor ("Tint Color", Color) = (.5, .5, .5, .5)
        _FrameValue("Frame remainder", Float) = 0
        [IntRange] _Frequency ("Frequency", Range(1,15)) = 1
        _fogInfluence("Fog Influence", Range(0,2)) = 0.5
        _fogSpeed("Fog Speed", Float) = 10.0
    }
        CGINCLUDE
        #include "UnityCG.cginc"
        #pragma target 2.0

        uniform sampler2D_half _MainTex;
        uniform sampler2D_half _BlurTex;
        uniform sampler2D _CameraDepthTexture;
        half3 _LightPos;
        half _NumSamples;
        half _Density;
        half _Weight;
        half _Decay;
        half _Exposure;
        half _Contrast;
        uniform half4 _Parameter;
        uniform half4 _MainTex_TexelSize;
        half4 _MainTex_ST;
        half _LightY;
        half _CosAngle;
        half4 _TintColor;
        half _PerpendicularFalloff;
        int _Frequency;
        float _fogInfluence;
        half _fogSpeed;



        struct appdata
        {
            float4 pos : POSITION;
            float2 uv : TEXCOORD0;
        };

        struct v2f
        {
            float4 pos : SV_POSITION;
            float2 uv  : TEXCOORD0;
        };

        struct v2f_withBlurCoordsSGX
        {
            float4 pos : SV_POSITION;
            half2 uv : TEXCOORD0;
            half4 offs[3] : TEXCOORD1;
        };

        static const half curve[7] = { 0.0205, 0.0855, 0.232, 0.324, 0.232, 0.0855, 0.0205 };  // gauss'ish blur weights

        half rand(half2 co)
                {
                    const half a = 2.9898f;
                    const half b = 78.233f;
                    const half c = 28.5453f;
                    const half dt = dot(co.xy ,half2(a,b));
                    const half sn = cos(abs(dt/3.14f));
                    return cos(frac(sin(sn) * c)* ((_Time.w * _fogSpeed) * _fogInfluence));
                }
////////////// accumulator for rays  /////////////////
        v2f vert( appdata v )
            {
                v2f o;
                o.pos = UnityObjectToClipPos (v.pos);
                o.uv = v.uv;
                return o;
            }


        half4 frag(v2f i) : COLOR
            {
                // Calculate floattor from pixel to light source in screen space.
                half4 light = half4(_LightPos.xyz,1);
                half2 deltaTexCoord = half2 (0,0);
                // get our y direction, and swap the direction the coordinates are plotted based on that
                // so that it looks correct regardless of current camera rotation- we decompose this
                //because it will not look right if we just add or subtract light.xy to i.uv
                deltaTexCoord = half2(light.y < 0.0h ? half2(i.uv.x + light.x, i.uv.y + light.y) : half2(i.uv.x - light.x, i.uv.y - light.y));

                // Divide by number of samples and scale by control factor.
                deltaTexCoord *= 1.0h / _NumSamples * _Density;

                // Store initial sample.
                half2 uv = i.uv;
                half3 color = tex2D(_MainTex, uv);

                // Set up illumination decay factor.
                half illuminationDecay = 1.0h;

                // Evaluate summation from Equation 3 NUM_SAMPLES iterations.
                float depth;
                half rate = _Frequency;

                for (int i = 1; i < _NumSamples + 1; i++)
                {
                    // Step sample location along ray.
                    uv -= deltaTexCoord;
                    // Retrieve sample at new location.
                    float sample = tex2D(_MainTex, uv);
                    half randomFactor = rand(uv.yx)*_fogInfluence * _Contrast;
                    float value = frac(i/rate);
                    float cast = Linear01Depth(tex2D(_CameraDepthTexture, uv)).r;
                    //calc depth value
                    depth = float(value !=0 ? float(cast * 1.5f):float(cast * (1-randomFactor)));
                    // Apply sample attenuation scale/decay factors.
                    sample *= illuminationDecay * (_Weight/ _NumSamples*4) * depth;
                    sample *= 2.5h;

                    // Accumulate combined color.
                    color += sample;
                    // Update exponential decay factor.
                    illuminationDecay *= _Decay;
                }
                // Output final color with a further scale control factor.
                return (max(half4(color * _Exposure, 1), 0.15h));
            }
/////////////// SGX Horizontal Blur /////////////////////////////
        v2f_withBlurCoordsSGX vertBlurHorizontalSGX (appdata_img v)
            {
                v2f_withBlurCoordsSGX o;
                o.pos = UnityObjectToClipPos(v.vertex);

                o.uv = UnityStereoScreenSpaceUVAdjust(v.texcoord.xy, _MainTex_ST);

                const half offsetMagnitude = _MainTex_TexelSize.x * _Parameter.x;
                o.offs[0] = UnityStereoScreenSpaceUVAdjust(v.texcoord.xyxy + offsetMagnitude * half4(-3.0h, 0.0h, 3.0h, 0.0h), _MainTex_ST);
                o.offs[1] = UnityStereoScreenSpaceUVAdjust(v.texcoord.xyxy + offsetMagnitude * half4(-2.0h, 0.0h, 2.0h, 0.0h), _MainTex_ST);
                o.offs[2] = UnityStereoScreenSpaceUVAdjust(v.texcoord.xyxy + offsetMagnitude * half4(-1.0h, 0.0h, 1.0h, 0.0h), _MainTex_ST);

                return o;
            }
/////////////// SGX Vertical Blur /////////////////////////////
        v2f_withBlurCoordsSGX vertBlurVerticalSGX (appdata_img v)
            {
                v2f_withBlurCoordsSGX o;
                o.pos = UnityObjectToClipPos(v.vertex);

                o.uv = half4(UnityStereoScreenSpaceUVAdjust(v.texcoord.xy, _MainTex_ST),1,1);

                const half offsetMagnitude = _MainTex_TexelSize.y * _Parameter.x;
                o.offs[0] = UnityStereoScreenSpaceUVAdjust(v.texcoord.xyxy + offsetMagnitude * half4(0.0h, -3.0h, 0.0h, 3.0h), _MainTex_ST);
                o.offs[1] = UnityStereoScreenSpaceUVAdjust(v.texcoord.xyxy + offsetMagnitude * half4(0.0h, -2.0h, 0.0h, 2.0h), _MainTex_ST);
                o.offs[2] = UnityStereoScreenSpaceUVAdjust(v.texcoord.xyxy + offsetMagnitude * half4(0.0h, -1.0h, 0.0h, 1.0h), _MainTex_ST);

                return o;
            }
///////////// SGX Frag  //////////////////////////////////////
        half4 fragBlurSGX ( v2f_withBlurCoordsSGX i ) : SV_Target
            {
                half2 uv = i.uv.xy;

                half4 color = tex2D(_MainTex, i.uv) * curve[3];

                for( int l = 0; l < 3; l++ )
                {
                    const half4 tapA = tex2D(_MainTex, i.offs[l].xy);
                    const half4 tapB = tex2D(_MainTex, i.offs[l].zw);
                    color += (tapA + tapB) * curve[l];
                }
                return color;
            }
/////////////// Composition /////////////////////////////
        v2f vertFinal(appdata i)
            {
                v2f o = (v2f)0;
                UNITY_INITIALIZE_OUTPUT(v2f, o);
                o.pos = UnityObjectToClipPos(i.pos);
                o.uv = (i.uv);
                return o;
            }

        half4 fragFinal(v2f i) : SV_Target
            {
                half4 light = half4(_LightPos.xyz,1);
                _CosAngle = 1- abs(cos(light.z));
                const fixed4 col = tex2D(_MainTex, i.uv);
                fixed4 sample = tex2D(_BlurTex, i.uv);
                const fixed contrast = _Contrast;
                const fixed4 finalSample = (((col) + (sample * 0.4h)) - 0.5h) * contrast + 0.445h; //final sampled color
                const fixed4 finalColor = (col + (col * 0.04h) - 0.01h); //final modulated base color
                fixed4 blitColor = lerp(finalSample, finalColor, (1 - _CosAngle - _PerpendicularFalloff)); //use falloff to fade effect out when _CosAngle nears 1 to mask artifacts
                return blitColor;
            }

        //
        v2f vertStencil(appdata v)
        {
                v2f o;
                o.pos = UnityObjectToClipPos (v.pos);
                o.uv = v.uv;
                return o;
        }
        half4 fragStencil (v2f i) : SV_Target
        {
            fixed4 col = _TintColor;
            return col;
        }

        ENDCG
    ////// Passes /////////////////////////////////////////////////////
    SubShader {
        ZTest Always
        Cull Off
        //0- calculate low resolution rays

        Pass {
                CGPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #pragma fragmentoption ARB_precision_hint_fastest
                ENDCG
            }
            //2- vertical blur
        Pass {
                CGPROGRAM
                #pragma vertex vertBlurVerticalSGX
                #pragma fragment fragBlurSGX
                #pragma fragmentoption ARB_precision_hint_fastest
                ENDCG
            }

        //3- horizontal Blur
        Pass {
                CGPROGRAM
                #pragma vertex vertBlurHorizontalSGX
                #pragma fragment fragBlurSGX
                #pragma fragmentoption ARB_precision_hint_fastest
                ENDCG
            }
        Pass //4- composition
        {
            CGPROGRAM
            #pragma vertex vertFinal
            #pragma fragment fragFinal
            #pragma fragmentoption ARB_precision_hint_fastest
            ENDCG
        }
        Pass {
        Stencil{
            Ref [_StencilRef]
            Comp Equal
            Pass Keep
        }
                CGPROGRAM
                #pragma vertex vertStencil
                #pragma fragment fragStencil
                #pragma fragmentoption ARB_precision_hint_fastest
                ENDCG
            }
    }
}