Colouring agents based on proximity to one another.

carlos_the_dwarf

Hello everyone. I have been playing with the Attraction 2D example as part of the verletphysics library. I currently have a situation where a number of particles arrange themselves at a random point on the screen. I would like to start colouring these agents . The agents closes to the centre of the arrangement should be red whilst the outer agents should be blue to give the impression of temperature. I have tried to use the map function to achieve this but I'm having trouble. Here's what I've got:

import toxi.geom.*;
import toxi.physics2d.*;
import toxi.physics2d.behaviors.*;
int countNeighbours=0;


int NUM_PARTICLES = 50;

VerletPhysics2D physics;
AttractionBehavior mouseAttractor;

Vec2D mousePos;
Vec2D target;
Vec2D randomTarget;

void setup() {
  size(600, 600, P3D);
  // setup physics with 10% drag
  physics = new VerletPhysics2D();
  physics.setDrag(0.05f);
  physics.setWorldBounds(new Rect(0, 0, width, height));
  // the NEW way to add gravity to the simulation, using behaviors
  //physics.addBehavior(new GravityBehavior(new Vec2D(0, 0.15f)));
  randomTarget = new Vec2D(random(0, width), random(0, height));
  // create a new positive attraction force field around the mouse position (radius=250px)
  mouseAttractor = new AttractionBehavior(randomTarget, width, .9f);
  physics.addBehavior(mouseAttractor);
}

void addParticle() {
  VerletParticle2D p = new VerletParticle2D(Vec2D.randomVector().scale(5).addSelf(width / 2, height/2));
  physics.addParticle(p);
  // add a negative attraction force field around the new particle
  physics.addBehavior(new AttractionBehavior(p, 20, -1.2f, 0.01f));
}

void draw() {
  background(255);
  noStroke();
  println(countNeighbours);

  fill(0);

  if (physics.particles.size() < NUM_PARTICLES) {
    addParticle();
  }
  physics.update();
  for (VerletParticle2D p : physics.particles) {
    ellipse(p.x, p.y, 5, 5);
  }
}

void mousePressed() {
  mousePos = new Vec2D(mouseX, mouseY);
  target = new Vec2D(300, 300);
  randomTarget = new Vec2D(random(0, width), random(0, height));
  // create a new positive attraction force field around the mouse position (radius=250px)
  mouseAttractor = new AttractionBehavior(randomTarget, width, .9f);
  physics.addBehavior(mouseAttractor);
}

//void mouseDragged() {
//  // update mouse attraction focal point
//  mousePos.set(mouseX, mouseY);
//}
//
void mouseReleased() {
  // remove the mouse attraction when button has been released
  mouseAttractor = new AttractionBehavior(mousePos, width, 0f);
  physics.addBehavior(mouseAttractor);
}