212 lines
6 KiB
GLSL
212 lines
6 KiB
GLSL
#version 120
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// Atmospheric scattering shader for flightgear
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// Written by Lauri Peltonen (Zan)
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// Implementation of O'Neil's algorithm
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// Ground haze layer added by Thorsten Renk
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varying vec3 rayleigh;
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varying vec3 mie;
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varying vec3 eye;
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varying vec3 hazeColor;
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varying float ct;
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//varying float cosphi;
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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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uniform float overcast;
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uniform float saturation;
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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 cloud_self_shading;
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const float EarthRadius = 5800000.0;
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float miePhase(in float cosTheta, in float g)
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{
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float g2 = g*g;
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float a = 1.5 * (1.0 - g2);
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float b = (2.0 + g2);
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float c = 1.0 + cosTheta*cosTheta;
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float d = pow(1.0 + g2 - 2.0 * g * cosTheta, 0.6667);
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return (a*c) / (b*d);
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}
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float rayleighPhase(in float cosTheta)
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{
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//return 1.5 * (1.0 + cosTheta*cosTheta);
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return 1.5 * (2.0 + 0.5*cosTheta*cosTheta);
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}
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void main()
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{
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vec3 shadedFogColor = vec3(0.65, 0.67, 0.78);
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float cosTheta = dot(normalize(eye), gl_LightSource[0].position.xyz);
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// position of the horizon line
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float lAltitude = alt + delta_z;
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float radiusEye = EarthRadius + alt;
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float radiusLayer = EarthRadius + lAltitude;
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float cthorizon;
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float ctterrain;
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if (radiusEye > radiusLayer) cthorizon = -sqrt(radiusEye * radiusEye - radiusLayer * radiusLayer)/radiusEye;
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else cthorizon = sqrt(radiusLayer * radiusLayer - radiusEye * radiusEye)/radiusLayer;
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ctterrain = -sqrt(radiusEye * radiusEye - EarthRadius * EarthRadius)/radiusEye;
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vec3 color = rayleigh * rayleighPhase(cosTheta);
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color += mie * miePhase(cosTheta, -0.8);
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vec3 black = vec3(0.0,0.0,0.0);
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float ovc = overcast;
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float sat = 1.0 - ((1.0 - saturation) * 2.0);
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if (sat < 0.3) sat = 0.3;
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// float wscale = 1.732;
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// an overexposure filter, the log() seems to be pretty expensive though
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// if (color.x > 0.8) color.x = 0.8 + 0.8* log(color.x/0.8);
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// if (color.y > 0.8) color.y = 0.8 + 0.8* log(color.y/0.8);
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// if (color.z > 0.8) color.z = 0.8 + 0.8* log(color.z/0.8);
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// a different exposure filter
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//color.x = 1.0 - exp(-1.3 * color.x);
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//color.y = 1.0 - exp(-1.3 * color.y);
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//color.z = 1.0 - exp(-1.3 * color.z);
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if (color.r > 0.58) color.r = 1.0 - exp(-1.5 * color.r);
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if (color.g > 0.58) color.g = 1.0 - exp(-1.5 * color.g);
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if (color.b > 0.58) color.b = 1.0 - exp(-1.5 * color.b);
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// reduce the whiteout near the horizon generated by the single scattering approximation
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//if (ct > cthorizon) color = mix(color, black ,smoothstep(0.2+cthorizon, -0.2+cthorizon, ct));
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//else color = mix (color, black, smoothstep(0.2+cthorizon,-0.2+cthorizon, cthorizon));
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// fog computations for a ground haze layer, extending from zero to lAltitude
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float transmission;
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float vAltitude;
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float delta_zv;
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float costheta = ct;
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float vis = min(visibility, avisibility);
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// hack - in an effect volume the visibility only may be reduced, so we take care here
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//if (avisibility < visibility){vis = avisibility;}
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if (delta_z > 0.0) // we're inside the layer
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{
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if (costheta>0.0 + ctterrain) // looking up, view ray intersecting upper layer edge
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{
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transmission = exp(-min((delta_z/max(costheta,0.1)),25000.0)/vis);
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//transmission = 1.0;
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vAltitude = min(vis * costheta, delta_z);
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delta_zv = delta_z - vAltitude;
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}
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else // looking down, view range intersecting terrain (which may not be drawn)
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{
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transmission = exp(alt/vis/costheta);
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vAltitude = min(-vis * costheta, alt);
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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
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{
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if (costheta < 0.0 + cthorizon)
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{
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transmission = exp(-min(lAltitude/abs(costheta),25000.0)/vis);
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transmission = transmission * exp(-alt/avisibility/abs(costheta));
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transmission = 1.0 - (1.0 - transmission) * smoothstep(0+cthorizon, -0.02+cthorizon, costheta);
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vAltitude = min(lAltitude, -vis * costheta);
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delta_zv = vAltitude;
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}
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else
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{
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transmission = 1.0;
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delta_zv = 0.0;
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}
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}
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// combined intensity reduction by cloud shading and fog self-shading, corrected for Weber-Fechner perception law
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//float scattering = ground_scattering + (1.0 - ground_scattering) * smoothstep(avisibility, 1.5 * avisibility, -alt/costheta);
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float eqColorFactor = 1.0 - 0.1 * delta_zv/vis - (1.0 - min(scattering,cloud_self_shading));
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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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// postprocessing of haze color
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vec3 hColor = hazeColor;
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// high altitude desaturation
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float intensity = length(hColor);
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hColor = intensity * normalize (mix(hColor, intensity * vec3 (1.0,1.0,1.0), 0.7* smoothstep(5000.0, 50000.0, alt)));
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// blue hue
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hColor.x = 0.83 * hColor.x;
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hColor.y = 0.9 * hColor.y;
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// further blueshift when in shadow, either cloud shadow, or self-shadow or Earth shadow, dependent on indirect
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// light
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float fade_out = max(0.65 - 0.3 *overcast, 0.45);
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intensity = length(hColor);
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vec3 oColor = hColor;
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oColor = intensity * normalize(mix(oColor, shadedFogColor, (smoothstep(0.1,1.0,ovc))));
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color = ovc * mix(color, oColor * earthShade ,smoothstep(-0.1+ctterrain, 0.0+ctterrain, ct)) + (1-ovc) * color;
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hColor = intensity * normalize(mix(hColor, 1.5 * shadedFogColor, 1.0 -smoothstep(0.25, fade_out,earthShade) ));
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hColor = intensity * normalize(mix(hColor, shadedFogColor, (1.0 - smoothstep(0.5,0.9,eqColorFactor))));
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//hColor = intensity * normalize(mix(hColor, shadedFogColor, (1.0 - smoothstep(0.5,0.9,cloud_self_shading)) ));
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hColor = hColor * earthShade;
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// accounting for overcast and saturation
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color = sat * color + (1.0 - sat) * mix(color, black, smoothstep(0.4+cthorizon,0.2+cthorizon,ct));
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// the terrain below the horizon gets drawn in one optical thickness
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vec3 terrainHazeColor = eqColorFactor * hColor;
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color = mix(color, terrainHazeColor ,smoothstep(0.01 + ctterrain, 0.0+ctterrain, ct));
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// mix fog the skydome with the right amount of haze
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color = transmission * color + (1.0-transmission) * eqColorFactor * hColor;
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gl_FragColor = vec4(color, 1.0);
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gl_FragDepth = 0.1;
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}
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