Canvas/33_canvas_圆角矩形.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')
      drawRoundRect(ctx, 100, 100, 600, 500, 50)
    }

    function drawRoundRect(ctx, x, y, width, height, radius) {
      ctx.save()

      ctx.translate(x, y)
      pathRect(ctx, width, height, radius)

      ctx.strokeStyle = 'black'

      ctx.stroke()

      ctx.restore()
    }

    function pathRect(ctx, w, h, r) {
      ctx.beginPath()

      ctx.arc(w - r, h - r, r, 0, Math.PI / 2)
      ctx.lineTo(r, h)

      ctx.arc(r, h - r, r, Math.PI / 2, Math.PI)
      ctx.lineTo(0, r)

      ctx.arc(r, r, r, Math.PI, Math.PI * 3 / 2)
      ctx.lineTo(w - r, 0)

      ctx.arc(w - r, r, r, Math.PI * 3 / 2, Math.PI * 2)

      ctx.closePath()
    }
  </script>
</body>

</html>