void drawParticle(float x, float y, float d, float theta)
{
  stroke(0);
  strokeWeight(1);
  noFill();

  ellipse(x,y,d,d);

  fill(0);
  noStroke();

  ellipse(x + 0.5*d*cos(theta), y + 0.5*d*sin(theta), 6, 6);
}

float xpos, ypos, ang, diam;

void setup()
{
  size(500,500);
}

void draw()
{
  background(255);
  for(int i=-1; i<21; i++)
    for(int j=-1; j<21; j++)
    {
      diam = 45;
      ang = TWO_PI*(i+j)/15 + TWO_PI*frameCount/50;
      xpos = map(i,0,19,5,width-5);
      ypos = map(j,0,19,5,height-5);
      drawParticle(xpos,ypos,diam,ang);
    }

  saveFrame("f##.png");

  if(frameCount==50)
    exit();
}