Canvas/22_canvas_图形变换累加机制.html

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>Page Title</title>
  <meta name="viewport" content="width=device-width, initial-scale=1">
</head>

<body>
  <canvas id="myCanvas" style="border:1px solid red;">
    当前浏览器不支持canvas，请更换浏览器后再试
  </canvas>
  <script>
    window.onload = function () {
      var canvas = document.getElementById('myCanvas')

      canvas.width = 800
      canvas.height = 800

      var ctx = canvas.getContext('2d')

      ctx.fillStyle = 'red'
      ctx.translate(100, 100)// 移动绘制原点到100,100处，所以fillRect实际绘制在100,100处
      ctx.fillRect(0, 0, 400, 400)

      ctx.fillStyle = 'blue'
      ctx.translate(300, 300)// 原本想将原点移动到300,300处，但是变形的计算是会累加的，所以最后fillRect将绘制在100+300=400,100+300=400处
      ctx.fillRect(0, 0, 400, 400)

    }
  </script>
</body>

</html>