Canvas/43_canvas_探照灯.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')

      function draw(ctx) {
        ctx.clearRect(0, 0, 800, 800)
        ctx.save()
        ctx.beginPath()
        ctx.fillStyle = 'black'
        ctx.fillRect(0, 0, 800, 800)

        ctx.beginPath()
        ctx.arc(x, 400, 150, 0, Math.PI * 2)

        ctx.fillStyle = '#fff'

        ctx.fill()

        ctx.clip() // 利用path创建一个剪辑区域，只有此剪辑区域内的绘制才可见

        ctx.font = '150px bold Arial'
        ctx.textAlign = 'center'
        ctx.textBaseLine = 'middle'

        ctx.fillStyle = '#058'

        ctx.fillText('CANVAS', canvas.width / 2, canvas.height / 2)
        ctx.restore()
      }

      var x = 150
      function step() {
        x++
        if (x > 650) {
          x = 150
        }
        draw(ctx)
        window.requestAnimationFrame(step)
      }

      window.requestAnimationFrame(step)

    }


  </script>
</body>

</html>