float a, b, c, d, x, y, xp, yp;
int x_, y_;
PFont f;

int i = 0;
int imax = 10000; //number of steps to take

int hit[][] = new int[1500][1000];

void setup() {
  size(1500, 1000, P3D);
  f = createFont("Arial", 16, true);
  a = 0.59;
  b = -3;
  c = -1.4;
  d = 1.2;
  xp = random(-2, 2);
  yp = random(-2, 2);
  background(0);
  fill(255, 0, 0);
  noStroke();
  textFont(f, 20);
  text("a = " + str(a) + "\nb = " + str(b) + "\nc = " + str(c) + "\nd = " + str(d), 10, 30);

  for (int j = 0; j < 1500; j++) {
    for (int k = 0; k < 1000; k++) {
      hit[j][k] = 0;
    }
  }
}

void draw() {
  //background(0);
  if (i < imax) {
  xp = random(-2,2);
  yp = random(-2,2);
  b = map(i, 0, imax, -3, -2); //set your interval here
  for (int j = 0; j < 50000; j++) { //set nuber of iterations
    x = sin(yp * b) - c * sin(xp * b);
    y = sin(xp * a) + d * sin(yp * a);
    xp = x;
    yp = y;
    x_ = int(map(i, 0, imax, 0, width));
    y_ = int(map(y, -1, 1, 1000, 0)); //set bound of y
    if (j > 5000 && x_ >= 0 && x_ < 1500 && y_ >= 0 && y_ < 1000) { //set number of omitted iterations
      hit[x_][y_] += 1;
      set(x_, y_, color(255));
    }
  }
  println(str(float(i)/imax * 100) + "% done");
  i++;
  } else {
    background(0);
    int max = 0;
    for (int j = 0; j < 1500; j++) {
      for (int k = 0; k < 1000; k++) {
        max = max(max, hit[j][k]);
      }
    }
    for (int j = 0; j < 1500; j++) {
      for (int k = 0; k < 1000; k++) {
        if (hit[j][k] > 0) {set(j, k, color(map(log(float(hit[j][k])), 0, log(max), 0, 255)));}
      }
    }
  fill(255, 0, 0);
  noStroke();
  textFont(f, 20);
  text("a = " + str(a) + "\nb = " + str(b) + "\nc = " + str(c) + "\nd = " + str(d), 10, 30);
  }
}