285 lines
7.4 KiB
C++
285 lines
7.4 KiB
C++
// -*-C++-*-
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// written by Thorsten Renk, Oct 2011, based on default.frag
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// Ambient term comes in gl_Color.rgb.
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varying vec4 diffuse_term;
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varying vec3 normal;
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varying vec3 relPos;
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//varying vec3 hazeColor;
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//varying float fogCoord;
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uniform sampler2D texture;
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//varying float ct;
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//varying float delta_z;
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//varying float alt;
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varying float earthShade;
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//varying float yprime;
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//varying float vertex_alt;
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varying float yprime_alt;
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varying float mie_angle;
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uniform float visibility;
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uniform float avisibility;
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uniform float scattering;
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uniform float terminator;
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uniform float terrain_alt;
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uniform float hazeLayerAltitude;
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uniform float overcast;
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//uniform float altitude;
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uniform float eye_alt;
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const float EarthRadius = 5800000.0;
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const float terminator_width = 200000.0;
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float alt;
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float luminance(vec3 color)
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{
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return dot(vec3(0.212671, 0.715160, 0.072169), color);
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}
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float light_func (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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// this determines how light is attenuated in the distance
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// physically this should be exp(-arg) but for technical reasons we use a sharper cutoff
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// for distance > visibility
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float fog_func (in float targ)
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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; // 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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void main()
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{
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// this is taken from default.frag
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vec3 n;
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float NdotL, NdotHV, fogFactor;
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vec4 color = gl_Color;
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vec3 lightDir = gl_LightSource[0].position.xyz;
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vec3 halfVector = gl_LightSource[0].halfVector.xyz;
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vec4 texel;
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vec4 fragColor;
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vec4 specular = vec4(0.0);
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float intensity;
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vec4 light_specular = gl_LightSource[0].specular;
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// If gl_Color.a == 0, this is a back-facing polygon and the
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// normal should be reversed.
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n = (2.0 * gl_Color.a - 1.0) * normal;
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n = normalize(n);
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NdotL = dot(n, lightDir);
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if (NdotL > 0.0) {
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color += diffuse_term * NdotL;
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NdotHV = max(dot(n, halfVector), 0.0);
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if (gl_FrontMaterial.shininess > 0.0)
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specular.rgb = (gl_FrontMaterial.specular.rgb
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* light_specular.rgb
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* pow(NdotHV, gl_FrontMaterial.shininess));
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}
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color.a = diffuse_term.a;
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// This shouldn't be necessary, but our lighting becomes very
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// saturated. Clamping the color before modulating by the texture
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// is closer to what the OpenGL fixed function pipeline does.
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color = clamp(color, 0.0, 1.0);
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texel = texture2D(texture, gl_TexCoord[0].st);
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fragColor = color * texel + specular;
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// here comes the terrain haze model
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float delta_z = hazeLayerAltitude - eye_alt;
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float dist = length(relPos);
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if (dist > 40.0)
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{
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alt = eye_alt;
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float transmission;
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float vAltitude;
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float delta_zv;
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float H;
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float distance_in_layer;
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float transmission_arg;
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// angle with horizon
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float ct = dot(vec3(0.0, 0.0, 1.0), relPos)/dist;
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// we solve the geometry what part of the light path is attenuated normally and what is through the haze layer
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if (delta_z > 0.0) // we're inside the layer
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{
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if (ct < 0.0) // we look down
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{
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distance_in_layer = dist;
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//lambda = visibility;
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vAltitude = min(distance_in_layer,visibility) * ct;
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delta_zv = delta_z - vAltitude;
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}
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else // we may look through upper layer edge
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{
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H = dist * ct;
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if (H > delta_z) {distance_in_layer = dist/H * delta_z;}
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else {distance_in_layer = dist;}
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//lambda = visibility;
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vAltitude = min(distance_in_layer,visibility) * ct;
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delta_zv = delta_z - vAltitude;
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}
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}
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else // we see the layer from above, delta_z < 0.0
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{
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H = dist * -ct;
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if (H < (-delta_z)) // we don't see into the layer at all, aloft visibility is the only fading
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{
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distance_in_layer = 0.0;
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delta_zv = 0.0;
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}
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else
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{
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vAltitude = H + delta_z;
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distance_in_layer = vAltitude/H * dist;
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vAltitude = min(distance_in_layer,visibility) * (-ct);
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delta_zv = vAltitude;
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}
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}
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// ground haze cannot be thinner than aloft visibility in the model,
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// so we need to use aloft visibility otherwise
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transmission_arg = (dist-distance_in_layer)/avisibility;
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float eqColorFactor;
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if (visibility < avisibility)
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{
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transmission_arg = transmission_arg + (distance_in_layer/visibility);
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// this combines the Weber-Fechner intensity
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eqColorFactor = 1.0 - 0.1 * delta_zv/visibility - (1.0 -scattering);
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}
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else
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{
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transmission_arg = transmission_arg + (distance_in_layer/avisibility);
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// this combines the Weber-Fechner intensity
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eqColorFactor = 1.0 - 0.1 * delta_zv/avisibility - (1.0 -scattering);
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}
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transmission = fog_func(transmission_arg);
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// there's always residual intensity, we should never be driven to zero
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if (eqColorFactor < 0.2) eqColorFactor = 0.2;
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float lightArg = (terminator-yprime_alt)/100000.0;
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vec3 hazeColor;
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hazeColor.b = light_func(lightArg, 1.330e-05, 0.264, 2.527, 1.08e-05, 1.0);
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hazeColor.g = light_func(lightArg, 3.931e-06, 0.264, 3.827, 7.93e-06, 1.0);
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hazeColor.r = light_func(lightArg, 8.305e-06, 0.161, 3.827, 3.04e-05, 1.0);
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// now dim the light for haze
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earthShade = 0.9 * smoothstep(terminator_width+ terminator, -terminator_width + terminator, yprime_alt) + 0.1;
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// Mie-like factor
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if (lightArg < 5.0)
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{intensity = length(hazeColor);
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float mie_magnitude = 0.5 * smoothstep(350000.0, 150000.0, terminator-sqrt(2.0 * EarthRadius * terrain_alt));
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hazeColor = intensity * ((1.0 - mie_magnitude) + mie_magnitude * mie_angle) * normalize(mix(hazeColor, vec3 (0.5, 0.58, 0.65), mie_magnitude * (0.5 - 0.5 * mie_angle)) );
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}
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// high altitude desaturation of the haze color
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intensity = length(hazeColor);
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hazeColor = intensity * normalize (mix(hazeColor, intensity * vec3 (1.0,1.0,1.0), 0.7* smoothstep(5000.0, 50000.0, alt)));
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// blue hue of haze
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hazeColor.x = hazeColor.x * 0.83;
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hazeColor.y = hazeColor.y * 0.9;
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// additional blue in indirect light
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float fade_out = max(0.65 - 0.3 *overcast, 0.45);
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intensity = length(hazeColor);
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hazeColor = intensity * normalize(mix(hazeColor, 1.5* vec3 (0.45, 0.6, 0.8), 1.0 -smoothstep(0.25, fade_out,earthShade) ));
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// change haze color to blue hue for strong fogging
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//intensity = length(hazeColor);
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hazeColor = intensity * normalize(mix(hazeColor, 2.0 * vec3 (0.55, 0.6, 0.8), (1.0-smoothstep(0.3,0.8,eqColorFactor))));
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// reduce haze intensity when looking at shaded surfaces, only in terminator region
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float shadow = mix( min(1.0 + dot(normal,lightDir),1.0), 1.0, 1.0-smoothstep(0.1, 0.4, transmission));
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hazeColor = mix(shadow * hazeColor, hazeColor, 0.3 + 0.7* smoothstep(250000.0, 400000.0, terminator));
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// determine the right mix of transmission and haze
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//fragColor.xyz = transmission * fragColor.xyz + (1.0-transmission) * eqColorFactor * hazeColor * earthShade;
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fragColor.xyz = mix(eqColorFactor * hazeColor * earthShade, fragColor.xyz,transmission);
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gl_FragColor = fragColor;
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}
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else // if dist < 40.0 no fogging at all
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{
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gl_FragColor = fragColor;
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}
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}
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