45 lines
1.5 KiB
GLSL
45 lines
1.5 KiB
GLSL
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uniform sampler2D currentParticlesPosition; // (lon, lat, lev)
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uniform sampler2D currentParticlesSpeed; // (u, v, w, normalization)
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varying vec2 v_textureCoordinates;
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vec2 lengthOfLonLat(vec3 lonLatLev) {
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// unit conversion: meters -> longitude latitude degrees
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// see https://en.wikipedia.org/wiki/Geographic_coordinate_system#Length_of_a_degree for detail
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// Calculate the length of a degree of latitude and longitude in meters
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float latitude = radians(lonLatLev.y);
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float term1 = 111132.92;
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float term2 = 559.82 * cos(2.0 * latitude);
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float term3 = 1.175 * cos(4.0 * latitude);
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float term4 = 0.0023 * cos(6.0 * latitude);
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float latLength = term1 - term2 + term3 - term4;
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float term5 = 111412.84 * cos(latitude);
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float term6 = 93.5 * cos(3.0 * latitude);
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float term7 = 0.118 * cos(5.0 * latitude);
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float longLength = term5 - term6 + term7;
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return vec2(longLength, latLength);
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}
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void updatePosition(vec3 lonLatLev, vec3 speed) {
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vec2 lonlatLengthgth = lengthOfLonLat(lonLatLev);
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float u = speed.x / lonlatLengthgth.x;
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float v = speed.y / lonlatLengthgth.y;
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float w = 0.0;
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vec3 windVectorInLonLatLev = vec3(u, v, w);
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vec3 nextParticle = lonLatLev + windVectorInLonLatLev;
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gl_FragColor = vec4(nextParticle, 0.0);
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}
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void main() {
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// texture coordinate must be normalized
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vec3 lonLatLev = texture2D(currentParticlesPosition, v_textureCoordinates).rgb;
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vec3 speed = texture2D(currentParticlesSpeed, v_textureCoordinates).rgb;
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updatePosition(lonLatLev, speed);
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}
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