var ball_num;
var ballX = [];
var ballY = [];
var speedX = [];
var speedY = [];
var ball_color = [];
var ball_diameter = [];

var colors = [];

function setup() {
  createCanvas(windowWidth,
               windowHeight);

  ball_num = 400;

  colors.push(color(192, 192, 192));
  colors.push(color(128, 128, 128));
  colors.push(color(64, 128, 170));
  colors.push(color(78, 160, 200));
  colors.push(color(180, 205, 230));
  colors.push(color(255, 180, 20));
  colors.push(color(20, 120, 150));
  colors.push(color(255, 80, 30));

  for (var i = 0; i < ball_num; i = i + 1) {
    ballX[i] = random(0, windowWidth);
    ballY[i] = random(0, windowHeight);
    speedX[i] = random(-1.0, 1.0);
    speedY[i] = random(-1.0, 1.0);
    ball_color[i] = floor(random(0, colors.length));
    ball_diameter[i] = random(5, 40);
  }
}

function draw() {
  background(230, 230, 230, 100);
  noStroke();

  for (var i = 0; i < ball_num; i++) {
    ballX[i] = ballX[i] + speedX[i];
    ballY[i] = ballY[i] + speedY[i];

    if (ballX[i] > windowWidth || ballX[i] < 0) {
      speedX[i] = -1 * speedX[i];
    }

    if (ballY[i] > windowHeight || ballY[i] < 0) {
      speedY[i] = -1 * speedY[i];
    }
  }

  for (var i = 0; i < ball_num; i++) {
    fill(colors[ball_color[i]]);
    ellipse(ballX[i], ballY[i], ball_diameter[i]);
  }

}