/** Query the texture for the colour at the given intersection (in 3D space). */
private Colour queryTexture(Vector3 intersection) {
Vector3 Vn = mNorth;
Vector3 Ve = Vector3.pool.borrow().reset(Vn.y, -Vn.x, 0.0); // (AKA Vn.cross(0, 0, 1))
Vector3 Vp = Vector3.pool.borrow().reset(intersection);
Vp.subtract(mPlanetOrigin);
Ve.normalize();
Vp.normalize();
double phi = Math.acos(-1.0 * Vector3.dot(Vn, Vp));
double v = phi / Math.PI;
double theta = (Math.acos(Vector3.dot(Vp, Ve) / Math.sin(phi))) / (Math.PI * 2.0);
double u;
Vector3 c = Vector3.cross(Vn, Ve);
if (Vector3.dot(c, Vp) > 0) {
u = theta;
} else {
u = 1.0 - theta;
}
Vector3.pool.release(c);
Vector3.pool.release(Ve);
Vector3.pool.release(Vp);
return mTexture.getTexel(u, v);
}
/**
* Calculates diffuse lighting at the given point with the given normal.
*
* @param normal Normal at the point we're calculating diffuse lighting for.
* @param point The point at which we're calculating diffuse lighting.
* @return The diffuse factor of lighting.
*/
private double diffuse(Vector3 normal, Vector3 point) {
Vector3 directionToLight = Vector3.pool.borrow().reset(mSunOrigin);
directionToLight.subtract(point);
directionToLight.normalize();
double factor = Vector3.dot(normal, directionToLight);
Vector3.pool.release(directionToLight);
return factor;
}
/**
* Calculates light intensity from the sun.
*
* @param intersection Point where the ray we're currently tracing intersects with the planet.
*/
private double lightSphere(Vector3 intersection) {
Vector3 surfaceNormal = Vector3.pool.borrow().reset(intersection);
surfaceNormal.subtract(mPlanetOrigin);
surfaceNormal.normalize();
double intensity = diffuse(surfaceNormal, intersection);
intensity = Math.max(mAmbient, Math.min(1.0, intensity));
Vector3.pool.release(surfaceNormal);
return intensity;
}
/**
* Computes the colour of the pixel at (x,y) where each coordinate is defined to be in the range
* (-0.5, +0.5).
*
* @param x The x-coordinate, between -0.5 and +0.5.
* @param y The y-coordinate, between -0.5 and +0.5.
* @return The colour at the given pixel.
*/
private Colour getPixelColour(double x, double y) {
Colour c = Colour.pool.borrow().reset(Colour.TRANSPARENT);
Vector3 ray = Vector3.pool.borrow().reset(x, -y, 1.0);
ray.normalize();
Vector3 intersection = raytrace(ray);
if (intersection != null) {
// we intersected with the planet. Now we need to work out the colour at this point
// on the planet.
Colour t = queryTexture(intersection);
double intensity = lightSphere(intersection);
c.reset(1.0, t.r * intensity, t.g * intensity, t.b * intensity);
Colour.pool.release(t);
if (mAtmospheres != null) {
Vector3 surfaceNormal = Vector3.pool.borrow().reset(intersection);
surfaceNormal.subtract(mPlanetOrigin);
surfaceNormal.normalize();
Vector3 sunDirection = Vector3.pool.borrow().reset(mSunOrigin);
sunDirection.subtract(intersection);
sunDirection.normalize();
final int numAtmospheres = mAtmospheres.size();
for (int i = 0; i < numAtmospheres; i++) {
final Atmosphere atmosphere = mAtmospheres.get(i);
Colour atmosphereColour =
atmosphere.getInnerPixelColour(
x + 0.5, y + 0.5, intersection, surfaceNormal, sunDirection);
Colour.blend(c, atmosphereColour);
Colour.pool.release(atmosphereColour);
}
Vector3.pool.release(surfaceNormal);
Vector3.pool.release(sunDirection);
}
} else if (mAtmospheres != null) {
// if we're rendering an atmosphere, we need to work out the distance of this ray
// to the planet's surface
double u = Vector3.dot(mPlanetOrigin, ray);
Vector3 closest = Vector3.pool.borrow().reset(ray);
closest.scale(u);
double distance = (Vector3.distanceBetween(closest, mPlanetOrigin) - mPlanetRadius);
Vector3 surfaceNormal = Vector3.pool.borrow().reset(closest);
surfaceNormal.subtract(mPlanetOrigin);
surfaceNormal.normalize();
Vector3 sunDirection = Vector3.pool.borrow().reset(mSunOrigin);
sunDirection.subtract(closest);
sunDirection.normalize();
final int numAtmospheres = mAtmospheres.size();
for (int i = 0; i < numAtmospheres; i++) {
final Atmosphere atmosphere = mAtmospheres.get(i);
Colour atmosphereColour =
atmosphere.getOuterPixelColour(x + 0.5, y + 0.5, surfaceNormal, distance, sunDirection);
Colour.blend(c, atmosphereColour);
Colour.pool.release(atmosphereColour);
}
Vector3.pool.release(closest);
Vector3.pool.release(surfaceNormal);
Vector3.pool.release(sunDirection);
}
Vector3.pool.release(ray);
Vector3.pool.release(intersection);
return c;
}