298 lines
10 KiB
GLSL
298 lines
10 KiB
GLSL
// -*-C++-*-
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#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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uniform mat4 osg_ViewMatrix;
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uniform mat4 osg_ViewMatrixInverse;
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uniform float hazeLayerAltitude;
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uniform float terminator;
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uniform float avisibility;
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uniform float visibility;
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uniform float terrain_alt;
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uniform float air_pollution;
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uniform float radius_modifier;
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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 vec3 viewVector;
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varying float ct;
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varying float cphi;
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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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// Dome parameters from FG and screen
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const float domeSize = 80000.0;
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const float realDomeSize = 100000.0;
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const float groundRadius = 0.984503332 * domeSize;
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const float altitudeScale = domeSize - groundRadius;
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const float EarthRadius = 5800000.0;
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// Dome parameters when calculating scattering
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// Assuming dome size is 5.0
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const float groundLevel = 0.984503332 * 5.0;
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const float heightScale = (5.0 - groundLevel);
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// Integration parameters
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const int nSamples = 7;
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const float fSamples = float(nSamples);
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// Scattering parameters
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uniform float rK = 0.0003; //0.00015;
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uniform float mK = 0.003; //0.0025;
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uniform float density = 0.5; //1.0
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//vec3 rayleighK = rK * vec3(5.602, 7.222, 19.644);
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vec3 rayleighK = rK * vec3(4.5, 8.62, 17.3);
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vec3 mieK = vec3(mK);
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vec3 sunIntensity = 10.0*vec3(120.0, 125.0, 130.0);
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// light_func is a generalized logistic function fit to the light intensity as a function
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// of scaled terminator position obtained from Flightgear core
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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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// Find intersections of ray to skydome
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// ray must be normalized
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// cheight is camera height
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float intersection (in float cheight, in vec3 ray, in float rad2)
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{
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float B = 2.0 * cheight*ray.y;
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float C = cheight*cheight - rad2; // 25.0 is skydome radius * radius
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float fDet = max(0.0, B*B - 4.0 * C);
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return 0.5 * (-B - sqrt(fDet));
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}
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// Return the scale function at height = 0 for different thetas
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float outscatterscale(in float costheta)
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{
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float x = 1.0 - costheta;
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float a = 1.16941;
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float b = 0.618989;
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float c = 6.34484;
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float d = -31.4138;
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float e = 75.3249;
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float f = -80.1643;
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float g = 32.2878;
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return exp(a+x*(b+x*(c+x*(d+x*(e+x*(f+x*g))))));
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}
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// Return the amount of outscatter for different heights and thetas
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// assuming view ray hits the skydome
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// height is 0 at ground level and 1 at space
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// Assuming average density of atmosphere is at 1/4 height
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// and atmosphere height is 100 km
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float outscatter(in float costheta, in float height)
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{
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return density * outscatterscale(costheta) * exp(-4.0 * height);
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}
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void main()
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{
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// Make sure the dome is of a correct size
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vec4 realVertex = gl_Vertex; //vec4(normalize(gl_Vertex.xyz) * domeSize, 1.0);
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// Ground point (skydome center) in eye coordinates
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vec4 groundPoint = gl_ModelViewMatrix * vec4(0.0, 0.0, 0.0, 1.0);
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// Calculate altitude as the distance from skydome center to camera
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// Make it so that 0.0 is ground level and 1.0 is 100km (space) level
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// the correction ensures compatibility with Earthview for orbits farther out
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float altitude = distance(groundPoint, vec4(0.0, 0.0, 0.0, 1.0)) * (1.0 -0.0013);
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float scaledAltitude = altitude / realDomeSize;
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// the local horizon angle
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float radiusEye = EarthRadius + altitude;
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float ctterrain = -sqrt(radiusEye * radiusEye - EarthRadius * EarthRadius)/radiusEye;
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// Camera's position, z is up!
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float cameraRealAltitude = groundLevel + heightScale*scaledAltitude;
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vec3 camera = vec3(0.0, 0.0, cameraRealAltitude);
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vec3 sample = 5.0 * realVertex.xyz / domeSize; // Sample is the dome vertex
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vec3 relativePosition = camera - sample; // Relative position
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viewVector = (sample-camera).xyz;
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// Find intersection of skydome and view ray
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float space = intersection(cameraRealAltitude, -normalize(relativePosition), 25.0);
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if(space > 0.0) {
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// We are in space, calculate correct positiondelta!
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relativePosition -= space * normalize(relativePosition);
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}
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vec3 positionDelta = relativePosition / fSamples;
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float deltaLength = length(positionDelta); // Should multiply by something?
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vec3 lightDirection = gl_LightSource[0].position.xyz;
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// Cos theta of camera's position and sample point
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// Since camera is 0,0,z, dot product is just the z coordinate
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float cameraCosTheta;
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// If sample is above camera, reverse ray direction
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if(positionDelta.z < 0.0) cameraCosTheta = -positionDelta.z / deltaLength;
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else cameraCosTheta = positionDelta.z / deltaLength;
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float cameraCosTheta1 = -positionDelta.z / deltaLength;
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// Total attenuation from camera to skydome
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float totalCameraScatter = outscatter(cameraCosTheta, scaledAltitude);
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// Do numerical integration of scattering function from skydome to camera
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vec3 color = vec3(0.0);
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// no scattering integrations where terrain is later drawn
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if (cameraCosTheta1 > (ctterrain-0.05))
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{
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for(int i = 0; i < nSamples; i++)
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{
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// Altitude of the sample point 0...1
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float sampleAltitude = (length(sample) - groundLevel) / heightScale;
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// Cosine between the angle of sample's up vector and sun
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// Since lightDirection is in eye space, we must transform sample too
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vec3 sampleUp = gl_NormalMatrix * normalize(sample);
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float cosTheta = dot(sampleUp, lightDirection);
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// Scattering from sky to sample point
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float skyScatter = outscatter(cosTheta, sampleAltitude);
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// Calculate the attenuation from this point to camera
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// Again, reverse the direction if vertex is over the camera
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float cameraScatter;
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if(relativePosition.z < 0.0) { // Vertex is over the camera
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cameraCosTheta = -dot(normalize(positionDelta), normalize(sample));
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cameraScatter = totalCameraScatter - outscatter(cameraCosTheta, sampleAltitude);
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} else { // Vertex is below camera
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cameraCosTheta = dot(normalize(positionDelta), normalize(sample));
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cameraScatter = outscatter(cameraCosTheta, sampleAltitude) - totalCameraScatter;
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}
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// Total attenuation
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vec3 totalAttenuate = 4.0 * 3.14159 * (rayleighK + mieK) * (-skyScatter - cameraScatter);
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vec3 inScatter = exp(totalAttenuate - sampleAltitude*4.0);
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color += inScatter * deltaLength;
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sample += positionDelta;
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}
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}
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color *= sunIntensity;
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ct = cameraCosTheta1;
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rayleigh = rayleighK * color;
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mie = mieK * color;
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eye = gl_NormalMatrix * positionDelta;
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// We need to move the camera so that the dome appears to be centered around earth
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// to make the dome render correctly!
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float moveDown = -altitude; // Center dome on camera
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moveDown += groundRadius;
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moveDown += scaledAltitude * altitudeScale; // And move correctly according to altitude
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// Vertex transformed correctly so that at 100km we are at space border
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vec4 finalVertex = realVertex - vec4(0.0, 0.0, 1.0, 0.0) * moveDown;
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// prepare some stuff for a ground haze layer
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delta_z = hazeLayerAltitude - altitude;
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alt = altitude;
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// establish coordinates relative to sun position
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vec4 ep = gl_ModelViewMatrixInverse * vec4(0.0,0.0,0.0,1.0);
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vec3 lightFull = (gl_ModelViewMatrixInverse * gl_LightSource[0].position).xyz;
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vec3 lightHorizon = normalize(vec3(lightFull.x,lightFull.y, 0.0) );
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vec3 relVector = normalize(finalVertex.xyz - ep.xyz);
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// and compute the twilight shading
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// yprime is the coordinate from/towards terminator
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float yprime;
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if (alt > hazeLayerAltitude) // we're looking from above and can see far
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{
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if (ct < 0.0)
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{
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yprime = -dot(relVector,lightHorizon) * altitude/-ct;//(ct-0.001);
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yprime = yprime -sqrt(2.0 * EarthRadius * hazeLayerAltitude);
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}
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else // the only haze we see looking up is overcast, assume its altitude
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{
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yprime = -dot(relVector,lightHorizon) * avisibility;
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yprime = yprime -sqrt(2.0 * EarthRadius * 10000.0);
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}
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}
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else
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{yprime = -dot(relVector,lightHorizon) * avisibility;
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yprime = yprime -sqrt(2.0 * EarthRadius * hazeLayerAltitude);
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}
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if (terminator > 1000000.0){yprime = -sqrt(2.0 * EarthRadius * hazeLayerAltitude);}
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float terminator_width = 200000.0;
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earthShade = 0.9 * smoothstep((terminator_width+ terminator), (-terminator_width + terminator), yprime) + 0.1;
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float lightArg = (terminator-yprime)/100000.0;
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hazeColor.r = light_func(lightArg, 8.305e-06, 0.161, 4.827-3.0*air_pollution, 3.04e-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.b = light_func(lightArg, 1.330e-05, 0.264, 1.527+2.0*air_pollution, 1.08e-05, 1.0);
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//new
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//hazeColor.r = light_func(lightArg, 3.495e-05, 0.161, 3.878, 0.000129, 1.0);
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//hazeColor.g = light_func(lightArg, 1.145e-05, 0.161, 3.827, 1.783e-05, 1.0);
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//hazeColor.b = light_func(lightArg, 0.234, 0.141, 2.572, 0.257, 1.0);
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float intensity = length(hazeColor.xyz);
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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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cphi = dot(normalize(relVector), normalize(lightHorizon));
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float mie_angle = (0.5 * dot(normalize(relVector), normalize(lightFull)) ) + 0.5;
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float mie_postfactor = clamp(mie_magnitude * (0.5 - 0.5 * mie_angle),0.001,1.0);
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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_postfactor ) );
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// Transform
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gl_Position = gl_ModelViewProjectionMatrix * finalVertex;
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}
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