体积雾 global fog unity

https://github.com/keijiro/KinoFog

lighting box 2.7.2

halfspace fog 相机位于一个位置 这个位置可以在fog volumn里面或者外面  雾开始的地方就是文中的plane

http://www.terathon.com/lengyel/Lengyel-UnifiedFog.pdf

这个fog volume可以从中间某个位置height 这个平面产生雾 远近浓度通过depth深度计算

还可以定义雾密度 

    // Applies one of standard fog formulas, given fog coordinate (i.e. distance)
    half ComputeFogFactor (float coord)
    {
        float fogFac = 0.0;
        if (_SceneFogMode.x == 1) // linear
        {
            // factor = (end-z)/(end-start) = z * (-1/(end-start)) + (end/(end-start))
            fogFac = coord * _SceneFogParams.z + _SceneFogParams.w;
        }
        if (_SceneFogMode.x == 2) // exp
        {
            // factor = exp(-density*z)
            fogFac = _SceneFogParams.y * coord; fogFac = exp2(-fogFac);
        }
        if (_SceneFogMode.x == 3) // exp2
        {
            // factor = exp(-(density*z)^2)
            fogFac = _SceneFogParams.x * coord; fogFac = exp2(-fogFac*fogFac);
        }
        return saturate(fogFac);
    }

    // Distance-based fog
    float ComputeDistance (float3 camDir, float zdepth)
    {
        float dist; 
        if (_SceneFogMode.y == 1)
            dist = length(camDir);
        else
            dist = zdepth * _ProjectionParams.z;
        // Built-in fog starts at near plane, so match that by
        // subtracting the near value. Not a perfect approximation
        // if near plane is very large, but good enough.
        dist -= _ProjectionParams.y;
        return dist;
    }

     float ComputeHalfSpace (float3 wsDir)
    {
        float3 wpos = _CameraWS + wsDir;
        float FH = _HeightParams.x;
        float3 C = _CameraWS;
        float3 V = wsDir;
        float3 P = wpos;
        float3 aV = _HeightParams.w * V;
        float FdotC = _HeightParams.y;
        float k = _HeightParams.z;
        float FdotP = P.y-FH;
        float FdotV = wsDir.y;
        float c1 = k * (FdotP + FdotC);
        float c2 = (1-2*k) * FdotP;
        float g = min(c2, 0.0);
        g = -length(aV) * (c1 - g * g / abs(FdotV+1.0e-5f));
        return g;
    }

FdocC = camPos.y-height.value;      height  就是halfplane所定义的高度 plane法线垂直向上