75 lines
1.7 KiB
GLSL
75 lines
1.7 KiB
GLSL
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// -*-C++-*-
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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 - 2.0 * 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(35000.0,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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