146 lines
3.5 KiB
C++
146 lines
3.5 KiB
C++
// -*-C++-*-
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uniform sampler2D texture;
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uniform float visibility;
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uniform float avisibility;
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uniform float hazeLayerAltitude;
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uniform float eye_alt;
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uniform float terminator;
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varying vec3 relPos;
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varying float pixelSize;
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float alt;
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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 * 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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float light_sprite (in vec2 coord, in float transmission)
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{
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coord.s = coord.s - 0.5;
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coord.t = coord.t - 0.5;
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float r = length(coord);
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if (pixelSize<1.3) {return vec4 (1.0,1.0,1.0,1.0) * 0.08;}
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float sinphi = dot(vec2 (1.0,0.0), normalize(coord));
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float ray = clamp(pow(sin((sinphi-3.0) * (sinphi-3.0)),10.0),0.0,1.0);
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float fogEffect = (1.0-smoothstep(0.4,0.8,transmission));
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float intensity = clamp(ray * exp(-40.0 * r * r) + exp(-80.0*r*r),0.0,1.0) + 0.1 * fogEffect * (1.0-smoothstep(0.3, 0.6,r));
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return vec4 (1.0,1.0,1.0,1.0) * intensity;
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}
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void main()
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{
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float dist = length(relPos);
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float delta_z = hazeLayerAltitude - 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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vAltitude = min(distance_in_layer,min(visibility, avisibility)) * 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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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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if (visibility < avisibility)
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{
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transmission_arg = transmission_arg + (distance_in_layer/visibility);
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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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}
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transmission = fog_func(transmission_arg);
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float lightArg = terminator/100000.0;
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float attenuationScale = 1.0 + 3.0 * (1.0 -smoothstep(-15.0, 0.0, lightArg));
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float dist_att = exp(-0.3/attenuationScale/pixelSize);
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//vec4 texel = texture2D(texture,gl_TexCoord[0].st);
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vec4 texel = light_sprite(gl_TexCoord[0].st,transmission);
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gl_FragColor = vec4 (gl_Color.rgb, texel.a * transmission * dist_att);
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}
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