source: data/contentcreation/pps/MarkusWegmann/Godray Shader Proof of Concept/Godrays_blur.cgfx @ 10256

struct OneTexelVertex {
    float4 Position     : POSITION;
    float2 UV           : TEXCOORD0;
};

//// Vertex Shader ////

OneTexelVertex ScreenQuadVS(
                float3 Position : POSITION, 
                float2 UV       : TEXCOORD0
) {
    OneTexelVertex OUT = (OneTexelVertex)0;
    OUT.Position = float4(Position, 1);
    OUT.UV = float2(UV.xy);
    return OUT;
}

OneTexelVertex ScreenQuadVSWithLightPosition(
                float3 Position : POSITION, 
                float2 UV       : TEXCOORD0,
                
                uniform float4x4 viewProj,
                uniform float4 sunLightPosition,
                
                out float2 projSunLightPosition : TEXCOORD1
) {
    OneTexelVertex OUT = (OneTexelVertex)0;
    OUT.Position = float4(Position, 1);
    OUT.UV = float2(UV.xy);
        
        projSunLightPosition = float2(0.5,0.5);
        
    return OUT;
}

//// Fragment Shader ////



void godray_blur(
        OneTexelVertex IN,

                float2 projSunLightPosition : TEXCOORD1,
                
        out float4 oColor: COLOR,
        
        uniform float exposure, 
        uniform float decay,
        uniform float density,
        uniform sampler2D decal)

{
        const int NUM_SAMPLES = 200;
        
        float2 texCoord = IN.UV;
        
        
        oColor = float4(0,0,0,1);
        
    float2 deltaTextCoord = IN.UV - projSunLightPosition;
    deltaTextCoord *= 1.0f / NUM_SAMPLES * density;

        float illuminationDecay = 1.0f;

    for(int i=0; i < NUM_SAMPLES; i++)
    {
        texCoord -= deltaTextCoord;
        float4 sample = tex2D(decal, texCoord);
                
                oColor += sample;
        sample *= illuminationDecay;

        illuminationDecay *= decay;
    }

    oColor *= exposure / NUM_SAMPLES;
}


void combineRenderAndGodrays(
        OneTexelVertex IN,

    out float4 color : COLOR,

    uniform sampler2D renderDecal,
    uniform sampler2D godraysDecal)
{
    color = tex2D(renderDecal, IN.UV) + tex2D(godraysDecal, IN.UV);
}

//// Variables ////
/////////////////////////////////////////////////////////////////////////////////////

float Script : STANDARDSGLOBAL <
    string UIWidget = "none";
    string ScriptClass = "scene";
    string ScriptOrder = "postprocess";
    string ScriptOutput = "color";
    string Script = "Technique=Main;";
> = 0.8;

float4 SunLightPosition /* : Position <
    string UIName =  "Sun Light Position";
    string Space = "World";
> */ = {0, 0, 0, 1};

float4 SkyColor <
    string UIName =  "Sky Color";
        string UIWidget = "Color";
> = {0f,0f,0f,1.0f};

float GodrayExposure = 1f;
float GodrayDecay = 0.1f;
float GodrayDensity = 0.7f;

texture ScnTarget : RenderColorTarget <
        float2 ViewPortRatio = {1,1};
    int MipLevels = 1;
    string Format = "X8R8G8B8" ;
    string UIWidget = "None";
>;

sampler2D ScnDecal = sampler_state {
    Texture = <ScnTarget>;
        WrapS = Repeat;
    WrapT = Repeat;
    MinFilter = Linear;
    MagFilter = Linear;
};

texture GodrayTarget : RenderColorTarget <
        float2 ViewPortRatio = {1,1};
    int MipLevels = 1;
    string Format = "X8R8G8B8" ;
    string UIWidget = "None";
>;

sampler2D GodrayDecal = sampler_state {
    Texture = <GodrayTarget>;
        WrapS = ClampToEdge;
    WrapT = ClampToEdge;
    MinFilter = Linear;
    MagFilter = Linear;
};

texture DepthBuffer : RENDERDEPTHSTENCILTARGET <
    float2 ViewPortRatio = {1,1};
    string Format = "D24S8";
    string UIWidget = "None";
>;

texture LowDepthBuffer : RENDERDEPTHSTENCILTARGET <
    float2 ViewPortRatio = {1,1};
    string Format = "D24S8";
    string UIWidget = "None";
>;
//// UN-TWEAKABLES - AUTOMATICALLY-TRACKED TRANSFORMS ////////////////

float4x4 WorldITXf : WorldInverseTranspose < string UIWidget="None"; >;
float4x4 WvpXf : WorldViewProjection < string UIWidget="None"; >;
float4x4 VpXf : ViewProjection < string UIWidget="None"; >;
float4x4 WorldXf : World < string UIWidget="None"; >;
float4x4 ViewIXf : ViewInverse < string UIWidget="None"; >;

// Standard full-screen imaging value

float ClearDepth <
    string UIWidget = "None";
> = 1.0;

float2 ViewportSize : VIEWPORTPIXELSIZE <
    string UIName="Screen Size";
    string UIWidget="None";
>;

technique Main <
        string Script =
        "RenderColorTarget0=ScnTarget;"
        "RenderDepthStencilTarget=DepthBuffer;"
                "ClearSetColor=SkyColor;"
                "ClearSetDepth=ClearDepth;"
                "Clear=Color;"
                "Clear=Depth;"
            "ScriptExternal=color;"
        "Pass=BlurRaw;"
        "Pass=CombineRender;";
>
{

        pass BlurRaw
        <
                string Script = "RenderColorTarget=GodrayTarget;"
                        "RenderDepthStencilTarget=LowDepthBuffer;"
                        "Draw=Buffer;";
    >
        {
                DepthTestEnable = false;
                DepthMask = false;
                BlendEnable = false;
                
                VertexShader = compile vp30 ScreenQuadVSWithLightPosition(VpXf, SunLightPosition);
        FragmentProgram = compile fp30 godray_blur(
                        GodrayExposure, 
                        GodrayDecay, 
                        GodrayDensity,
                        ScnDecal);
        }
        
        pass CombineRender
        <
                string Script = "RenderColorTarget0=;"
                        "RenderDepthStencilTarget=;"
                        "Draw=Buffer;";
    >
        {
                DepthTestEnable = false;
                DepthMask = false;
                BlendEnable = false;
                
                VertexShader = compile vp30 ScreenQuadVS();
        FragmentProgram = compile fp30 combineRenderAndGodrays(
                        ScnDecal,
                        GodrayDecal);
        }
}