Web Front-endH5 TutorialHow to wrap canvas text? Introduction to the method of wrapping text in canvasHow to wrap canvas text? Introduction to the method of wrapping text in canvas
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: 'sans-serif';
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 = $('#canvas'),
$editable = $('#editable'),
$hideText = $('#hideText'),
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, '<span>$1</span>');
html = html.replace(/\n|\r/ig, '<br>');
html = html.replace(/\s/ig, ' ');
return html;
}
function drawText () {
ctx.clearRect(0, 0, $(canvas).width(), $(canvas).height());
var fontSize = $hideText.css('fontSize');
ctx.font = fontSize + ' sans-serif';
ctx.textAlign = 'conter';
ctx.textBaseline = "top";
ctx.fillStyle = 'red';
$.each($("#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：
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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