ArrayList <Particle> particles;
PImage img;

float r,g,b;
int x,y,loc,locP;
color c; //image pixel color
color cP; //particle color
  int frameCounter = 0;


void setup() {
  size(420,600);
  img = loadImage("fisk_mississippi_map.jpg");
  frameRate(30);
  getColor();
  particles = new ArrayList<Particle>();
} //setup()

void draw() {
  smooth();
  noStroke();
  background(50,50);

// frameCounter+= 1;  //Track frameCount
  
  particles.add(new Particle(0,0));
  
  Iterator<Particle> it = particles.iterator();
  while (it.hasNext()) {
    Particle p = it.next();
    
  PVector wind = new PVector(random(-0.1,0.1),random(-0.3,0.1));
  PVector gravity = new PVector(0,0.1);
  
  p.applyForce(wind);
  p.applyForce(gravity);
  p.update();

  
//  if (frameCounter%30 == 0) {    //Change particle color incrementally
    //This worked with single particle, but not arrayList
    
    //Relate particle location to underlying image pixel:
  if((p.pH.x > 0) && (p.pH.x < width)) {
      if((p.pH.y > 0) && (p.pH.y < height)) {
        locP = (int)p.pH.x + (int)p.pH.y*width;
  }} else {
    locP = 0;
  }

      r = red  (img.pixels[locP]);
      g = green(img.pixels[locP]);
      b = blue (img.pixels[locP]);
      
      cP = color(r,g,b);
//  }  
  p.display(cP); //pass underlying pixel color to particle
  
  if (p.isDead())
  it.remove();
  
}} //draw()

  void getColor() {
  loadPixels();
  img.loadPixels();

  for (x=0; x<width; x++) {
    for (y=0; y<height; y++) {
      loc = x + y*width;

      r = red  (img.pixels[loc]);
      g = green(img.pixels[loc]);
      b = blue (img.pixels[loc]);
      
      c = color(r,g,b);
      pixels[loc] = c;
    }
  }
} //getColor()