/*

   Structure 3

   A surface filled with one hundred medium to small sized circles.
   Each circle has a different size and direction, but moves at the same slow rate.
   Display:
   >>> A. The instantaneous intersections of the circles
   B. The aggregate intersections of the circles

   Implemented by Casey Reas <http://groupc.net>
   8 March 2004
   Processing v.68 <http://processing.org>

*/

int numCircle = 100;
Circle[] circles = new Circle[numCircle];

void setup()
{
  size(800, 600);
  framerate(30);
  for(int i=0; i<numCircle; i++) {
    circles[i] = new Circle(random(width), (float)height/(float)numCircle * i,
                            int(random(1, 6))*10, random(-1.0, 1.0), random(-1.0, 1.0), i);
  }
  ellipseMode(CENTER_DIAMETER);
  background(255);
}


void loop()
{
  background(255);
  stroke(0);
  for(int i=0; i<numCircle; i++) {
    circles[i].update();
  }
  for(int i=0; i<numCircle; i++) {
    circles[i].move();
  }
  for(int i=0; i<numCircle; i++) {
    circles[i].makepoint();
  }
  noFill();
}


class Circle
{
  float x, y, r, r2, sp, ysp;
  int id;

  Circle( float px, float py, float pr, float psp, float pysp, int pid ) {
    x = px;
    y = py;
    r = pr;
    r2 = r*r;
    id = pid;
    sp = psp;
    ysp = pysp;
  }

  void update() {
    for(int i=0; i<numCircle; i++) {
      if(i != id) {
        intersect( this, circles[i] );
      }
    }
  }

  void makepoint() {
     stroke(0);
     point(x, y);
  }

  void move() {
    x += sp;
    y += ysp;
    if(sp > 0) {
      if(x > width+r) {
        x = -r;
      }
    } else {
      if(x < -r) {
        x = width+r;
      }
    }
    if(ysp > 0) {
      if(y > height+r) {
        y = -r;
      }
    } else {
      if(y < -r) {
        y = height+r;
      }
    }
  }
}

void intersect( Circle cA, Circle cB )
{
  float dx = cA.x - cB.x;
  float dy = cA.y - cB.y;
  float d2 = dx*dx + dy*dy;
  float d = sqrt( d2 );

  if ( d>cA.r+cB.r || d<abs(cA.r-cB.r) ) {
    return; // no solution
  }

  float a = (cA.r2 - cB.r2 + d2) / (2*d);
  float h = sqrt( cA.r2 - a*a );
  float x2 = cA.x + a*(cB.x - cA.x)/d;
  float y2 = cA.y + a*(cB.y - cA.y)/d;

  float paX = x2 + h*(cB.y - cA.y)/d;
  float paY = y2 - h*(cB.x - cA.x)/d;
  float pbX = x2 - h*(cB.y - cA.y)/d;
  float pbY = y2 + h*(cB.x - cA.x)/d;

  stroke(255-dist(paX, paY, pbX, pbY)*4);
  line(paX, paY, pbX, pbY);
}