canvas小球擺動效果

admin發表於2018-03-15
Canvas

下面是一個非常簡單的運動效果，類似於鐘錶一樣，小球可以左右擺動。

程式碼例項如下：

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<!DOCTYPE html>
<html>
<head>
<meta charset=" utf-8">
<meta name="author" content="http://www.softwhy.com/" />
<title>螞蟻部落</title>
<style>
html,body,canvas{
  width:100vw;
  height:100vh;
  background:#000000;
  overflow:hidden;
}
</style>
<script>
setTimeout(() => {
  let canvas = document.querySelector('canvas');
  let context = canvas.getContext('2d');
  canvas.width = canvas.offsetWidth;
  canvas.height = canvas.offsetHeight;

  let pointer = {
    x: canvas.width / 2,
    y: canvas.height / 4
  };

  let angleInit = Math.PI / 6;
  let angle;

  let render = function () {
    context.clearRect(0, 0, canvas.width, canvas.height);   
    // 小球
    context.save();
    context.fillStyle = "green";
    context.translate(pointer.x, pointer.y);
    context.rotate(angle);
    context.beginPath();
    context.arc(0, 200, 30, 0, 2 * Math.PI, false);
    context.fill();

    context.strokeStyle = "gray";
    context.lineWidth = 2;
    context.beginPath();
    context.moveTo(0, 0);
    context.lineTo(0, 200);
    context.stroke();
    context.restore();
  };

  let reverse = false;
  let run;
  (run = (time) => {
    if (!time) {
      angle = angleInit;
    }
   angle = angleInit * Math.cos(6 * time / 1000)
   render();
   requestAnimationFrame(run)
  })();
}, 500);
</script>
</head>
<body>
<canvas></canvas>
</body>
</html>

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