float angle = 0.0;
float speed = 0.025; // Play with this!!! (Default 0.03)
float direction = 1; // Play with this too. (Default = 1)
float r = width/40;
float x;
boolean toggleLoop = true;

void setup() {
  size(600, 400);
  //noStroke();
  smooth();
  background(0);
  float speed = 1;
  frameRate (120);
}

void draw() {
  fill(0, 2);
  //rect(0, 0, width, height);
  stroke (random(225, 255), random (175, 200), random (150), random(50, 100));
  //fill(255);
  angle = angle + speed;
  float amp = height/9; //amplitude (Default = height/9)
  float y = (height/2) + (sin(angle + (.5*PI)) * amp); // starts at top.*
  r = (width/40); // allows for resized window.

  ellipse (x, y, r, r); // show Y axis oscillation example
  //point (x, y); // This really slows things down.
  x = x + direction;

  if ((x > width) || (x < width - width)) {

    direction = -direction;
  }
}

// Mouse toggle code by amnon.owed
// http://forum.processing.org/topic/mouse-toggle-loop
// Place boolean toggleLoop = true; above setup.
void mousePressed() {
  if (mouseButton == LEFT) {
    if (toggleLoop) { 
      noLoop(); 
      toggleLoop = false;
    }
    else { 
      loop(); 
      toggleLoop = true;
    }
  }
}

//R.A.Robertson, adapted from "Processing" Chapter 32_3, Reas & Fry
// see also Reas & Fry Chapter 31_2.