104 lines
2.5 KiB
GLSL
104 lines
2.5 KiB
GLSL
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// -*-C++-*-
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#version 120
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uniform float air_pollution;
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// standard ALS fog function with exp(-d/D) fading and cutoff at low altitude and exp(-d^2/D^2) at high altitude
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const float AtmosphericScaleHeight = 8500.0;
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float fog_func (in float targ, in float alt)
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{
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float fade_mix;
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// for large altitude > 30 km, we switch to some component of quadratic distance fading to
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// create the illusion of improved visibility range
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targ = 1.25 * targ * smoothstep(0.04,0.06,targ); // need to sync with the distance to which terrain is drawn
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if (alt < 30000.0)
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{return exp(-targ - targ * targ * targ * targ);}
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else if (alt < 50000.0)
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{
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fade_mix = (alt - 30000.0)/20000.0;
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return fade_mix * exp(-targ*targ - pow(targ,4.0)) + (1.0 - fade_mix) * exp(-targ - pow(targ,4.0));
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}
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else
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{
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return exp(- targ * targ - pow(targ,4.0));
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}
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}
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// altitude correction for exponential drop in atmosphere density
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float alt_factor(in float eye_alt, in float vertex_alt)
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{
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float h0 = AtmosphericScaleHeight;
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float h1 = min(eye_alt,vertex_alt);
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float h2 = max(eye_alt,vertex_alt);
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if ((h2-h1) < 200.0) // use a Taylor-expanded version
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{
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return 0.5 * (exp(-h2/h0) + exp(-h1/h0));
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}
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else
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{
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return h0/(h2-h1) * (exp(-h1/h0) - exp(-h2/h0));
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}
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}
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// Rayleigh in-scatter function
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float rayleigh_in_func(in float dist, in float air_pollution, in float avisibility, in float eye_alt, in float vertex_alt)
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{
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float fade_length = avisibility * (2.5 - 2.2 * sqrt(air_pollution));
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fade_length = fade_length / alt_factor(eye_alt, vertex_alt);
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return 1.0-exp(-dist/max(15000.0,fade_length));
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}
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// Rayleigh out-scattering color shift
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vec3 rayleigh_out_shift(in vec3 color, in float outscatter)
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{
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color.r = color.r * (1.0 - 0.4 * outscatter);
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color.g = color.g * (1.0 - 0.8 * outscatter);
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color.b = color.b * (1.0 - 1.6 * outscatter);
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return color;
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}
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// the generalized logistic function used to compute lightcurves
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float light_curve (in float x, in float a, in float b, in float c, in float d, in float e)
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{
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x = x - 0.5;
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// use the asymptotics to shorten computations
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if (x > 30.0) {return e;}
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if (x < -15.0) {return 0.0;}
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return e / pow((1.0 + a * exp(-b * (x-c)) ),(1.0/d));
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}
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// the haze color function
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vec3 get_hazeColor(in float lightArg)
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{
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vec3 hazeColor;
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hazeColor.r = light_curve(lightArg, 8.305e-06, 0.161, 4.827-3.0 *air_pollution, 3.04e-05, 1.0);
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hazeColor.g = light_curve(lightArg, 3.931e-06, 0.264, 3.827, 7.93e-06, 1.0);
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hazeColor.b = light_curve(lightArg, 1.330e-05, 0.264, 1.527+ 2.0*air_pollution, 1.08e-05, 1.0);
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return hazeColor;
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}
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