game/动画

//这是自己写的


var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var raf;

var ball = {
  x: 100,
  y: 100,
  vx: 5,
  vy: 2,
  radius: 25,
  color: 'blue',
  draw: function() {
    ctx.beginPath();
    ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);
    ctx.closePath();
    ctx.fillStyle = this.color;
    ctx.fill();
  }
};

function draw() {
  ctx.fillStyle = 'rgba(255,255,255,0.3)';
  ctx.fillRect(0,0,canvas.width,canvas.height);
  ball.draw();
  ball.x += ball.vx;
  ball.y += ball.vy;
  ball.vy *= .99;
  ball.vy += .25;

  if (ball.y + ball.vy > canvas.height ||
      ball.y + ball.vy < 0) {
    ball.vy = -ball.vy;
  }
  if (ball.x + ball.vx > canvas.width ||
      ball.x + ball.vx < 0) {
    ball.vx = -ball.vx;
  }

  raf = window.requestAnimationFrame(draw);
}

canvas.addEventListener('mouseover', function(e){
  raf = window.requestAnimationFrame(draw);
});

canvas.addEventListener('mouseout', function(e){
  window.cancelAnimationFrame(raf);
});

ball.draw();//这是源码  地址：https://developer.mozilla.org/zh-CN/docs/Web/API/Canvas_API/Tutorial/Advanced_animations