public void updateDrawData() {
mBGStarPositionsBuffer.position(0);
mBGStarColorsBuffer.position(0);
mBGStarTexturesBuffer.position(0);
// Update the star data
for (Star star : BGStarSet) {
Geocentric position = star.getCoords();
Geocentric u = MathUtils.normalize(MathUtils.crossProduct(position, Z_UP_VECTOR));
Geocentric v = MathUtils.crossProduct(u, position);
float sizer = star.magnitude * mRenderer.mPointSizeFactor;
Geocentric sized_u = new Geocentric(u.x * sizer, u.y * sizer, u.z * sizer);
Geocentric sized_v = new Geocentric(v.x * sizer, v.y * sizer, v.z * sizer);
float[] bottomLeft = {
position.x - sized_u.x - sized_v.x,
position.y - sized_u.y - sized_v.y,
position.z - sized_u.z - sized_v.z
};
float[] topLeft = {
position.x - sized_u.x + sized_v.x,
position.y - sized_u.y + sized_v.y,
position.z - sized_u.z + sized_v.z
};
float[] bottomRight = {
position.x + sized_u.x - sized_v.x,
position.y + sized_u.y - sized_v.y,
position.z + sized_u.z - sized_v.z
};
float[] topRight = {
position.x + sized_u.x + sized_v.x,
position.y + sized_u.y + sized_v.y,
position.z + sized_u.z + sized_v.z
};
// Inserting first triangle (counter-clockwise)
mBGStarPositionsBuffer.put(topLeft);
mBGStarPositionsBuffer.put(bottomLeft);
mBGStarPositionsBuffer.put(topRight);
// Inserting second triangle (counter-clockwise)
mBGStarPositionsBuffer.put(bottomLeft);
mBGStarPositionsBuffer.put(bottomRight);
mBGStarPositionsBuffer.put(topRight);
// Inserting Color per Star (white)
mBGStarColorsBuffer.put(STAR_COLOR_DATA_ARRAY);
// Inserting Texture Coordinates per Star
mBGStarTexturesBuffer.put(TEX_COORD_ARRAY);
}
mBGStarPositionsBuffer.position(0);
mBGStarColorsBuffer.position(0);
mBGStarTexturesBuffer.position(0);
}
public void BuildBGStars() {
for (int i = 0; i < mNumBGStars; i++) {
// random.nextFloat() will return [0.0, 1.0)
Random random = new Random();
// RA must be 0 < RA < 360 degrees
float randomRA = random.nextFloat() * 360.0f;
// Declination is weighted to make background stars more visually appealing and spaced out
/* randomCent Values:
* 0-3 : 0
* 4-9 : 1
* 10-18 : 2
* 19-30 : 3
* 31-42 : 4
* 43-57 : 5
* 58-69 : 6
* 70-81 : 7
* 82-90 : 8
* 91-96 : 9
* 97-100 : 10
*/
float r = random.nextFloat() * 100.0f;
float randomDecZone = 0;
if (r <= 3) {
randomDecZone = 0;
} else if (r <= 9) {
randomDecZone = 1;
} else if (r <= 18) {
randomDecZone = 2;
} else if (r <= 30) {
randomDecZone = 3;
} else if (r <= 42) {
randomDecZone = 4;
} else if (r <= 57) {
randomDecZone = 5;
} else if (r <= 69) {
randomDecZone = 6;
} else if (r <= 81) {
randomDecZone = 7;
} else if (r <= 90) {
randomDecZone = 8;
} else if (r <= 96) {
randomDecZone = 9;
} else if (r <= 100) {
randomDecZone = 10;
}
// Declination range of one "DecZone" =~ 16.3635 degrees
// algorithm is (decZone number) + (range within decZone) - (offset == 90.0)
float randomDec = (randomDecZone * 16.3635f) + (random.nextFloat() * 16.3635f) - 90.0f;
// Dec must be (-90) < Dec < +90 degrees
RaDec randomRaDec = new RaDec(randomRA, randomDec);
// magnitude of background stars should be small, trying (minMag = 6.0) to (maxMag = 4.5)
float randomMag = (random.nextFloat() * 1.5f) + 4.5f;
randomMag =
(MAGNITUDE_SCALE * (Math.abs(randomMag - MIN_MAGNITUDE) / MAGNITUDE_RANGE))
+ POINT_SIZE_MIN_PIXELS;
Star star = new Star(randomRaDec);
star.setMagnitude(randomMag);
BGStarSet.add(star);
}
}