PImage img;
void setup() {
  img = loadImage("spiralthing.png");
  image(img, 0, 0);
  size(1000, 1000);
}
void draw() {
}
int tocheck[] = new int[100000];
int tcsize = 0;
void floodFill(int x, int y) {
  loadPixels();
  int startpoint = x + y*width;
  tocheck[0] = startpoint;
  tcsize = 1;
  while (tcsize > 0) {
    // Check to see if the last pixel in tocheck needs to be filled
    // If not, move on to the next pixel
    // If so, add the neighbors to tocheck if they need to be filled
    tcsize--;
    int curr = tocheck[tcsize];
    if (red(pixels[curr]) < 128) {
      pixels[curr] = color(255, 0, 0);
      if(curr - width > 0 && red(pixels[curr - width]) < 128 ){
         tocheck[tcsize] = curr - width;
         tcsize++;
      }
      if(curr + width < (height * width) && red(pixels[curr + width]) < 128 ){
         tocheck[tcsize] = curr + width;
         tcsize++;
      }
      if(curr - 1 > 0 && red(pixels[curr - 1]) < 128 ){
         tocheck[tcsize] = curr - 1;
         tcsize++;
      }
      if(curr + 1 < width*height && red(pixels[curr + 1]) < 128 ){
         tocheck[tcsize] = curr + 1;
         tcsize++;
      }
    }
  }
  updatePixels();
}
void mouseClicked() {
  floodFill(mouseX, mouseY);
}