Analytic Fog Rendering with Volumetric Primitives (2025)(matejlou.blog)

    // Assume: 
    // vec3 fogColor;      // Base fog color
    // float density;      // Fog density at point
    // vec3 lightDir;      // Direction from point to light
    // vec3 viewDir;       // Direction from camera to point
    // vec3 sunColor;      // RGB color of light

    // Compute angle between light and view
    float cosTheta = dot(normalize(lightDir), normalize(viewDir));

    // Simple Rayleigh-ish phase function (forward/backward scattering)
    float phase = 0.75 * (1.0 + cosTheta * cosTheta);

    // Wavelength-dependent scattering (approx Rayleigh)
    vec3 sigma = vec3(0.5, 0.8, 1.0); // R,G,B scattering coeffs

    // Fog contribution
    vec3 fogContribution = density * phase * sigma * sunColor;

    // Blend with scene color (sceneColor comes from existing render)
    vec3 finalColor = mix(sceneColor, sceneColor + fogContribution, density);