/**
* Base Perlin noise generator - fills height map with raw Perlin noise.
*
* This runs several iterations with increasing precision; the last iteration looks at areas
* of 1 by 1 tiles, the second to last at 2 by 2 tiles and the initial 2**MAX_TGP_FREQUENCIES
* by 2**MAX_TGP_FREQUENCIES tiles.
*/
static void HeightMapGenerate()
{
/* Trying to apply noise to uninitialized height map */
assert(_height_map.h != NULL);
int start = max(MAX_TGP_FREQUENCIES - (int)min(MapLogX(), MapLogY()), 0);
bool first = true;
for (int frequency = start; frequency < MAX_TGP_FREQUENCIES; frequency++) {
const amplitude_t amplitude = GetAmplitude(frequency);
/* Ignore zero amplitudes; it means our map isn't height enough for this
* amplitude, so ignore it and continue with the next set of amplitude. */
if (amplitude == 0) continue;
const int step = 1 << (MAX_TGP_FREQUENCIES - frequency - 1);
if (first) {
/* This is first round, we need to establish base heights with step = size_min */
for (int y = 0; y <= _height_map.size_y; y += step) {
for (int x = 0; x <= _height_map.size_x; x += step) {
height_t height = (amplitude > 0) ? RandomHeight(amplitude) : 0;
_height_map.height(x, y) = height;
}
}
first = false;
continue;
}
/* It is regular iteration round.
* Interpolate height values at odd x, even y tiles */
for (int y = 0; y <= _height_map.size_y; y += 2 * step) {
for (int x = 0; x <= _height_map.size_x - 2 * step; x += 2 * step) {
height_t h00 = _height_map.height(x + 0 * step, y);
height_t h02 = _height_map.height(x + 2 * step, y);
height_t h01 = (h00 + h02) / 2;
_height_map.height(x + 1 * step, y) = h01;
}
}
/* Interpolate height values at odd y tiles */
for (int y = 0; y <= _height_map.size_y - 2 * step; y += 2 * step) {
for (int x = 0; x <= _height_map.size_x; x += step) {
height_t h00 = _height_map.height(x, y + 0 * step);
height_t h20 = _height_map.height(x, y + 2 * step);
height_t h10 = (h00 + h20) / 2;
_height_map.height(x, y + 1 * step) = h10;
}
}
/* Add noise for next higher frequency (smaller steps) */
for (int y = 0; y <= _height_map.size_y; y += step) {
for (int x = 0; x <= _height_map.size_x; x += step) {
_height_map.height(x, y) += RandomHeight(amplitude);
}
}
}
}
/**
* One interpolation and noise round
*
* The heights on the map are generated in an iterative process.
* We start off with a frequency of 1 (log_frequency == 0), and generate heights only for corners on the most coarsly mesh
* (i.e. only for x/y coordinates which are multiples of the minimum edge length).
*
* After this initial step the frequency is doubled (log_frequency incremented) each iteration to generate corners on the next finer mesh.
* The heights of the newly added corners are first set by interpolating the heights from the previous iteration.
* Finally noise with the given amplitude is applied to all corners of the new mesh.
*
* Generation terminates, when the frequency has reached the map size. I.e. the mesh is as fine as the map, and every corner height
* has been set.
*
* @param log_frequency frequency (logarithmic) to apply noise for
* @param amplitude Amplitude for the noise
* @return false if we are finished (reached the minimal step size / highest frequency)
*/
static bool ApplyNoise(uint log_frequency, amplitude_t amplitude)
{
uint size_min = min(_height_map.size_x, _height_map.size_y);
uint step = size_min >> log_frequency;
uint x, y;
/* Trying to apply noise to uninitialized height map */
assert(_height_map.h != NULL);
/* Are we finished? */
if (step == 0) return false;
if (log_frequency == 0) {
/* This is first round, we need to establish base heights with step = size_min */
for (y = 0; y <= _height_map.size_y; y += step) {
for (x = 0; x <= _height_map.size_x; x += step) {
height_t height = (amplitude > 0) ? RandomHeight(amplitude) : 0;
_height_map.height(x, y) = height;
}
}
return true;
}
/* It is regular iteration round.
* Interpolate height values at odd x, even y tiles */
for (y = 0; y <= _height_map.size_y; y += 2 * step) {
for (x = 0; x < _height_map.size_x; x += 2 * step) {
height_t h00 = _height_map.height(x + 0 * step, y);
height_t h02 = _height_map.height(x + 2 * step, y);
height_t h01 = (h00 + h02) / 2;
_height_map.height(x + 1 * step, y) = h01;
}
}
/* Interpolate height values at odd y tiles */
for (y = 0; y < _height_map.size_y; y += 2 * step) {
for (x = 0; x <= _height_map.size_x; x += step) {
height_t h00 = _height_map.height(x, y + 0 * step);
height_t h20 = _height_map.height(x, y + 2 * step);
height_t h10 = (h00 + h20) / 2;
_height_map.height(x, y + 1 * step) = h10;
}
}
/* Add noise for next higher frequency (smaller steps) */
for (y = 0; y <= _height_map.size_y; y += step) {
for (x = 0; x <= _height_map.size_x; x += step) {
_height_map.height(x, y) += RandomHeight(amplitude);
}
}
return (step > 1);
}