状态堆栈

代码运行

<!DOCTYPE HTML>
<html>
  <head>
    <title>状态堆栈</title>
    <style>
      body {
        margin: 0px;
        padding: 0px;
      }
    </style>
  </head>
  <body>
    <canvas id="myCanvas" width="578" height="200"></canvas>
    <script>
      var canvas = document.getElementById('myCanvas');
      var context = canvas.getContext('2d');
      var rectWidth = 150;
      var rectHeight = 75;

context.save();
      // save state 1
      context.translate(canvas.width / 2, canvas.height / 2);

context.save();
      // save state 2
      context.rotate(Math.PI / 4);

context.save();
      // save state 3
      context.scale(2, 2);

context.fillStyle = 'blue';
      context.fillRect(rectWidth / -2, rectHeight / -2, rectWidth, rectHeight);

context.restore();
      // restore state 3
      context.fillStyle = 'red';
      context.fillRect(rectWidth / -2, rectHeight / -2, rectWidth, rectHeight);

context.restore();
      // restore state 2
      context.fillStyle = 'yellow';
      context.fillRect(rectWidth / -2, rectHeight / -2, rectWidth, rectHeight);

context.restore();
      // restore state 1
      context.fillStyle = 'green';
      context.fillRect(rectWidth / -2, rectHeight / -2, rectWidth, rectHeight);

</script>
  </body>
</html>