let position; //位置

let velocity; //速度

​

function setup() {

  createCanvas(windowWidth, windowHeight);

  diameter = 100.0;

  position = createVector(width / 2, height / 2);

  velocity = createVector(random(-2, 2), random(2, 2));

  background(0);

}

​

function draw() {

  background(0, 100);

  move(); //移動

  bounce(); //壁でバウンド

  display(); //表示

}

​

function move() {

  position.add(velocity);

}

​

function bounce() {

  if (position.x < diameter / 2 || position.x > width - diameter / 2) {

    velocity.x *= -1;

  }

  if (position.y < diameter / 2 || position.y > height - diameter / 2) {

    velocity.y *= -1;

  }

}

​

function display() {

  noStroke();

  fill(255, 63);

  let currentDiameter = sin(frameCount * 0.1) * (diameter / 4) + diameter;

  circle(position.x, position.y, currentDiameter);

  fill(255, 31, 31, 190);

  circle(position.x, position.y, diameter / 6.0);

}