commonMain.earth.worldwind.layer.atmosphere.SkyProgram.kt Maven / Gradle / Ivy
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The WorldWind Kotlin SDK (WWK) includes the library, examples and tutorials for building multiplatform 3D virtual globe applications for Android, Web and Java.
package earth.worldwind.layer.atmosphere
open class SkyProgram : AbstractAtmosphereProgram() {
override var programSources = arrayOf(
"""
const int SAMPLE_COUNT = 2;
const float SAMPLES = 2.0;
uniform int fragMode;
uniform mat4 mvpMatrix;
uniform mat3 texCoordMatrix;
uniform vec3 vertexOrigin;
uniform vec3 eyePoint;
uniform float eyeMagnitude; /* The eye point's magnitude */
uniform float eyeMagnitude2; /* eyeMagnitude^2 */
uniform mediump vec3 lightDirection;/* The light direction vector is used in both shaders, so we must use a common precision. */
uniform vec3 invWavelength; /* 1 / pow(wavelength, 4) for the red, green, and blue channels */
uniform float atmosphereRadius; /* The outer (atmosphere) radius */
uniform float atmosphereRadius2; /* atmosphereRadius^2 */
uniform float globeRadius; /* The inner (planetary) radius */
uniform float KrESun; /* Kr * ESun */
uniform float KmESun; /* Km * ESun */
uniform float Kr4PI; /* Kr * 4 * PI */
uniform float Km4PI; /* Km * 4 * PI */
uniform float scale; /* 1 / (atmosphereRadius - globeRadius) */
uniform float scaleDepth; /* The scale depth (i.e. the altitude at which the atmosphere's average density is found) */
uniform float scaleOverScaleDepth; /* fScale / fScaleDepth */
attribute vec4 vertexPoint;
attribute vec2 vertexTexCoord;
varying vec3 primaryColor;
varying vec3 secondaryColor;
varying vec3 direction;
varying vec2 texCoord;
float scaleFunc(float cos) {
float x = 1.0 - cos;
return scaleDepth * exp(-0.00287 + x*(0.459 + x*(3.83 + x*(-6.80 + x*5.25))));
}
void main() {
/* Get the ray from the camera to the vertex and its length (which is the far point of the ray passing through the
atmosphere) */
vec3 point = vertexPoint.xyz + vertexOrigin;
vec3 ray = point - eyePoint;
float far = length(ray);
ray /= far;
vec3 start;
float startOffset;
if (eyeMagnitude < atmosphereRadius) {
/* Calculate the ray's starting point, then calculate its scattering offset */
start = eyePoint;
float height = length(start);
float depth = exp(scaleOverScaleDepth * (globeRadius - eyeMagnitude));
float startAngle = dot(ray, start) / height;
startOffset = depth*scaleFunc(startAngle);
} else {
/* Calculate the closest intersection of the ray with the outer atmosphere (which is the near point of the ray
passing through the atmosphere) */
float B = 2.0 * dot(eyePoint, ray);
float C = eyeMagnitude2 - atmosphereRadius2;
float det = max(0.0, B*B - 4.0 * C);
float near = 0.5 * (-B - sqrt(det));
/* Calculate the ray's starting point, then calculate its scattering offset */
start = eyePoint + ray * near;
far -= near;
float startAngle = dot(ray, start) / atmosphereRadius;
float startDepth = exp(-1.0 / scaleDepth);
startOffset = startDepth*scaleFunc(startAngle);
}
/* Initialize the scattering loop variables */
float sampleLength = far / SAMPLES;
float scaledLength = sampleLength * scale;
vec3 sampleRay = ray * sampleLength;
vec3 samplePoint = start + sampleRay * 0.5;
/* Now loop through the sample rays */
vec3 frontColor = vec3(0.0, 0.0, 0.0);
for(int i=0; i