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How to wrap canvas text? Introduction to the method of wrapping text in canvas

不言Original: 2018-09-26 14:01:219028browse

html5中的canvas是用于绘制图形的，可以通过 JavaScript 来控制它绘制各种文本和图像，但是在使用 canvas 绘制文字的时候，我们可能想要让这些文字在某处按要求换行，这该如何实现呢？本篇文章将来给大家介绍关于canvas文字换行的方法，话不多说，下面我们来一起看看具体的内容。

在canvas中提供了将文本作为图片输出到画布上的功能，通常用到的函数主要有canvas.drawText 和canvas.fillText两个。

以canvas.fillText()函数为例，在canvas.fillText("information" , width , height , maxwidth )中包含四个参数，"information"表示文本输出的内容，width和height分别表示你想要输出的文本起始字符左上角的位置，而maxwidth则表示了该字符串的最大宽度，例如将maxwidth设为100，则无论字符串有多长，都将限制在100像素宽度内。

接下来我们来看一看将canvas文字换行的代码：

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>canvas自动换行</title>
  <style type="text/css">
    * {
      margin: 0
    }
    #main {
      width: 400px;
      margin: 20px auto 0;
    }
    #canvas, #editableWarp, #editable, #hideText {
      width: 400px;
      height: 125px;
      padding: 0;
      border: 0;
      background: pink;
      color: blue;
      font-size: 14px;
      font-family: &#39;sans-serif&#39;;
      position: relative;
      z-index: 1
    }
    #hideText {
      z-index: 0;
      position: absolute;
      　word-break: break-word;
      word-wrap: break-word;
    }
    p {
      line-height: 32px;
    }
  </style>
</head>
<body>
  <div id="main">
    <p>
      输入：
    </p>
    <div id="editableWarp">
      <div id="hideText"></div>
      <textarea id="editable" placeholder="请输入文字..."></textarea>
    </div>
    <p>
      canvas输出：
    </p>
    <canvas id="canvas" width="400" height="125">您的浏览器不支持canvas</canvas>
  </div>
  <script type="text/javascript" src="http://apps.bdimg.com/libs/jquery/2.1.4/jquery.min.js"></script>
  <script type="text/javascript">
    var $canvas = $(&#39;#canvas&#39;),
        $editable = $(&#39;#editable&#39;),
        $hideText = $(&#39;#hideText&#39;),
        ctx = $(canvas)[0].getContext("2d");
    $editable.keyup(function handleEdittable () {
      var txt = $editable.val(),
          html = convertText(txt);
      $hideText.html(html);
      drawText();
    });
    function convertText(txt) {
      var html = txt.replace(/(\S)/ig, &#39;<span>$1</span>&#39;);
      html = html.replace(/\n|\r/ig, &#39;<br>&#39;);
      html = html.replace(/\s/ig, &#39; &#39;);
      return html;
    }
    function drawText () {
      ctx.clearRect(0, 0, $(canvas).width(), $(canvas).height());
      var fontSize = $hideText.css(&#39;fontSize&#39;);
      ctx.font = fontSize + &#39; sans-serif&#39;;
      ctx.textAlign = &#39;conter&#39;;
      ctx.textBaseline = "top";
      ctx.fillStyle = &#39;red&#39;;
      $.each($("#hideText span"), function (i, item) {
        var pos = $(item).position();
        var txt = $(item).text();
        ctx.fillText(txt, pos.left, pos.top);
      });
    }
  </script>
</body>
</html>

canvas换行效果如下：

How to wrap canvas text? Introduction to the method of wrapping text in canvas

本篇文章到这里就结束了，关于canvas元素更多的知识可以参考HTML5开发手册学习具体内容。

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