perlin_noise.cpp

#include "util.h"
#include "perlin_noise.h"

void addAvg(int x, int y, const Table<double>& wys, double& avg, int& num) {
  Vec2 pos(x, y);
  if (pos.inRectangle(wys.getBounds())) {
    avg += wys[pos];
    ++num;
  }
}

Table<double> genNoiseMap(RandomGen& random, Rectangle area, NoiseInit init, double varianceMult) {
  int width = 1;
  while (width < area.width() - 1 || width < area.height() - 1)
    width *= 2;
  width /= 2;
  ++width;
  Table<double> wys(width, width);
  wys[0][0] = init.topLeft;
  wys[width - 1][0] = init.topRight;
  wys[width - 1][width - 1] = init.bottomRight;
  wys[0][width - 1] = init.bottomLeft;
  wys[(width - 1) / 2][(width - 1) / 2] = init.middle;

  double variance = 0.5;
  double heightDiff = 0.1;
  for (int a = width - 1; a >= 2; a /= 2) {
    if (a < width - 1)
      for (Vec2 pos1 : Rectangle((width - 1) / a, (width - 1) / a)) {
        Vec2 pos = pos1 * a;
        double avg = (wys[pos] + wys[pos.x + a][pos.y] + wys[pos.x][pos.y + a] + wys[pos.x + a][pos.y + a]) / 4;
        wys[pos.x + a / 2][pos.y + a / 2] =
            avg + variance * (random.getDouble() * 2 - 1);
      }
    for (Vec2 pos1 : Rectangle((width - 1) / a, (width - 1) / a + 1)) {
      Vec2 pos = pos1 * a;
      double avg = 0;
      int num = 0;
      addAvg(pos.x + a / 2, pos.y - a / 2, wys, avg, num);
      addAvg(pos.x, pos.y, wys, avg, num);
      addAvg(pos.x + a, pos.y, wys, avg, num);
      addAvg(pos.x + a / 2, pos.y + a / 2, wys, avg, num);
      wys[pos.x + a / 2][pos.y] =
          avg / num + variance * (random.getDouble() * 2 - 1);
    }
    for (Vec2 pos1 : Rectangle((width - 1) / a + 1, (width - 1) / a)) {
      Vec2 pos = pos1 * a;
      double avg = 0;
      int num = 0;
      addAvg(pos.x - a / 2, pos.y + a / 2, wys, avg, num);
      addAvg(pos.x, pos.y, wys, avg, num);
      addAvg(pos.x, pos.y + a , wys, avg, num);
      addAvg(pos.x + a / 2, pos.y + a / 2, wys, avg, num);
      wys[pos.x][pos.y + a / 2] =
          avg / num + variance * (random.getDouble() * 2 - 1);
    }
    variance *= varianceMult;
  }
  Table<double> ret(area);
  Vec2 offset(area.left(), area.top());
  for (Vec2 v : area) {
    Vec2 lv((v.x - offset.x) * width / area.width(), (v.y - offset.y) * width / area.height());
    ret[v] = wys[lv];
  }
  return ret;
}