extinction_calculation.hlsl

float4 PSMain(float4 position : SV_POSITION, float2 uv : TEXCOORD0 ) : SV_Target
{
    const float cExtinctionFactor = Params.Config.x;
    const float cDensity          = Params.Config.y;
    const int   cNumSamples       = Params.Config.z;
    const float cCutoffDist       = Params.Config.w;

    const float  depth = Depth.Sample(PointSampler, uv).r;
    const float4 vsPos = float4(screen_to_view(Params.Projection, uv, depth), 1.0f);
    const float  distToPos = length(vsPos);
    const float sampleLength = distToPos / float(cNumSamples);

    if ( distToPos > cCutoffDist )
        return float4(0.0f.xxx, 1.0f);

    float transmittance = 1.0;
    float3 inScattering = 0.0f.xxx;
    const float extinction = cExtinctionFactor * cDensity;

    for (int i = 0; i < cNumSamples; ++i)
    {
        float beerLawIntegral = exp(-extinction * sampleLength);
        transmittance *=  beerLawIntegral;
        inScattering  += Params.FogColor; // Should be retrieved from 3D texture
    }
    inScattering /= cNumSamples;

    return float4(inScattering * (1 - transmittance), transmittance);
}