// -*-C++-*- // standard ALS fog function with exp(-d/D) fading and cutoff at low altitude and exp(-d^2/D^2) at high altitude const float AtmosphericScaleHeight = 8500.0; float fog_func (in float targ, in float alt) { float fade_mix; // for large altitude > 30 km, we switch to some component of quadratic distance fading to // create the illusion of improved visibility range targ = 1.25 * targ * smoothstep(0.04,0.06,targ); // need to sync with the distance to which terrain is drawn if (alt < 30000.0) {return exp(-targ - targ * targ * targ * targ);} else if (alt < 50000.0) { fade_mix = (alt - 30000.0)/20000.0; return fade_mix * exp(-targ*targ - pow(targ,4.0)) + (1.0 - fade_mix) * exp(-targ - pow(targ,4.0)); } else { return exp(- targ * targ - pow(targ,4.0)); } } // altitude correction for exponential drop in atmosphere density float alt_factor(in float eye_alt, in float vertex_alt) { float h0 = AtmosphericScaleHeight; float h1 = min(eye_alt,vertex_alt); float h2 = max(eye_alt,vertex_alt); if ((h2-h1) < 200.0) // use a Taylor-expanded version { return 0.5 * (exp(-h2/h0) + exp(-h1/h0)); } else { return h0/(h2-h1) * (exp(-h1/h0) - exp(-h2/h0)); } } // Rayleigh in-scatter function float rayleigh_in_func(in float dist, in float air_pollution, in float avisibility, in float eye_alt, in float vertex_alt) { float fade_length = avisibility * (2.5 - 2.0 * air_pollution); fade_length = fade_length / alt_factor(eye_alt, vertex_alt); return 1.0-exp(-dist/max(35000.0,fade_length)); } // Rayleigh out-scattering color shift vec3 rayleigh_out_shift(in vec3 color, in float outscatter) { color.r = color.r * (1.0 - 0.4 * outscatter); color.g = color.g * (1.0 - 0.8 * outscatter); color.b = color.b * (1.0 - 1.6 * outscatter); return color; }