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https://thingvellir.net/git/overte
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76 lines
2.8 KiB
GLSL
76 lines
2.8 KiB
GLSL
//
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// Atmospheric scattering vertex shader
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//
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// Author: Sean O'Neil
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//
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// Copyright (c) 2004 Sean O'Neil
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//
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#version 120
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uniform vec3 v3CameraPos; // The camera's current position
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uniform vec3 v3LightPos; // The direction vector to the light source
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uniform vec3 v3InvWavelength; // 1 / pow(wavelength, 4) for the red, green, and blue channels
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uniform float fInnerRadius; // The inner (planetary) radius
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uniform float fKrESun; // Kr * ESun
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uniform float fKmESun; // Km * ESun
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uniform float fKr4PI; // Kr * 4 * PI
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uniform float fKm4PI; // Km * 4 * PI
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uniform float fScale; // 1 / (fOuterRadius - fInnerRadius)
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uniform float fScaleDepth; // The scale depth (i.e. the altitude at which the atmosphere's average density is found)
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uniform float fScaleOverScaleDepth; // fScale / fScaleDepth
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const int nSamples = 2;
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const float fSamples = 2.0;
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varying vec3 v3Direction;
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float scale(float fCos)
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{
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float x = 1.0 - fCos;
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return fScaleDepth * exp(-0.00287 + x*(0.459 + x*(3.83 + x*(-6.80 + x*5.25))));
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}
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void main(void)
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{
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// Get the ray from the camera to the vertex, and its length (which is the far point of the ray passing through the atmosphere)
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vec3 v3Pos = gl_Vertex.xyz;
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vec3 v3Ray = v3Pos - v3CameraPos;
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float fFar = length(v3Ray);
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v3Ray /= fFar;
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// Calculate the ray's starting position, then calculate its scattering offset
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vec3 v3Start = v3CameraPos;
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float fHeight = length(v3Start);
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float fDepth = exp(fScaleOverScaleDepth * (fInnerRadius - fHeight));
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float fStartAngle = dot(v3Ray, v3Start) / fHeight;
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float fStartOffset = fDepth*scale(fStartAngle);
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// Initialize the scattering loop variables
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//gl_FrontColor = vec4(0.0, 0.0, 0.0, 0.0);
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float fSampleLength = fFar / fSamples;
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float fScaledLength = fSampleLength * fScale;
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vec3 v3SampleRay = v3Ray * fSampleLength;
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vec3 v3SamplePoint = v3Start + v3SampleRay * 0.5;
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// Now loop through the sample rays
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vec3 v3FrontColor = vec3(0.0, 0.0, 0.0);
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for(int i=0; i<nSamples; i++)
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{
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float fHeight = length(v3SamplePoint);
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float fDepth = exp(fScaleOverScaleDepth * (fInnerRadius - fHeight));
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float fLightAngle = dot(v3LightPos, v3SamplePoint) / fHeight;
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float fCameraAngle = dot(v3Ray, v3SamplePoint) / fHeight;
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float fScatter = (fStartOffset + fDepth*(scale(fLightAngle) - scale(fCameraAngle)));
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vec3 v3Attenuate = exp(-fScatter * (v3InvWavelength * fKr4PI + fKm4PI));
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v3FrontColor += v3Attenuate * (fDepth * fScaledLength);
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v3SamplePoint += v3SampleRay;
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}
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// Finally, scale the Mie and Rayleigh colors and set up the varying variables for the pixel shader
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gl_FrontSecondaryColor.rgb = v3FrontColor * fKmESun;
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gl_FrontColor.rgb = v3FrontColor * (v3InvWavelength * fKrESun);
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gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
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v3Direction = v3CameraPos - v3Pos;
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}
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