canvas自定义扩展方法：文字自动换行

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在上一篇文章中，我们了解了 canvas如何新增属性和方法来自定义扩展，这篇文章，我们引用别人的一个扩展方法，文字自动换行。具体的使用示例，请参考示例源代码。进一步的讲解，请参考后面的参考资料链接。

示例效果图

示例源代码（共86行）

/*
* @Author: 大剑师兰特（xiaozhuanlan），还是大剑师兰特（CSDN）
* @此源代码版权归大剑师兰特所有，可供学习或商业项目中借鉴，未经授权，不得重复地发表到博客、论坛，问答，git等公共空间或网站中。
* @Email: [e-mail]
* @weixin: gis-dajianshi
* @First published in CSDN
* @First published time: 2024-02-01
*/
<template>
	<div class="djs_container">
		<div class="top">
			<h3>canvas自定义扩展：文字自动换行</h3>
			<div>大剑师兰特, 还是大剑师兰特，gis-dajianshi</div>
			<h4>
				<el-button type="primary" size="mini" @click="draw()">绘制</el-button>
				<el-button type="danger" size="mini" @click="clearCanvas()">清除</el-button>
			</h4>
		</div>
		<div class="dajianshi ">
			<canvas id="dajianshi" ref="mycanvas" width="980" height="490"></canvas>
		</div>
	</div>
</template>
<script>
	export default {
		data() {
			return {
				ctx: null,
				canvas: null,
			}
		},
		mounted() {
			this.setCanvas()
		},
		methods: {
			clearCanvas() {
				this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
			},
			setCanvas() {
				this.canvas = document.getElementById('dajianshi');
				if (!this.canvas.getContext) return;
				this.ctx = this.canvas.getContext("2d");

				CanvasRenderingContext2D.prototype.wrapText = function(text, x, y, maxWidth, lineHeight) {
					if (typeof text != 'string' || typeof x != 'number' || typeof y != 'number') {
						return;
					}

					var context = this;
					var canvas = context.canvas;

					if (typeof maxWidth == 'undefined') {
						maxWidth = (canvas && canvas.width) || 300;
					}
					if (typeof lineHeight == 'undefined') {
						lineHeight = (canvas && parseInt(window.getComputedStyle(canvas).lineHeight)) || parseInt(
							window.getComputedStyle(document.body).lineHeight);
					}

					// 字符分隔为数组
					var arrText = text.split('');
					var line = '';

					for (var n = 0; n < arrText.length; n++) {
						var testLine = line + arrText[n];
						var metrics = context.measureText(testLine);
						var testWidth = metrics.width;
						if (testWidth > maxWidth && n > 0) {
							context.fillText(line, x, y);
							line = arrText[n];
							y += lineHeight;
						} else {
							line = testLine;
						}
					}
					context.fillText(line, x, y);
				};

			},
			draw() {
                let txt='还是大剑师兰特：美国某知名大学研究生，专业的航天航海交通领域高级前端开发工程师，从事GIS、物联网行业多年，深耕vue+openlayers，vue+cesium，vue+mapbox，vue+leaflet等领域。'
				this.ctx.fillStyle = 'orange';
				this.ctx.font = '28px STheiti, SimHei';
				this.ctx.wrapText(txt, 340, 100, 400, 50)
			},

		}
	}
</script>
<style scoped>
	.djs_container {
		width: 1000px;
		height: 680px;
		margin: 50px auto;
		border: 1px solid #991188;
		position: relative;
	}

	.top {
		margin: 0 auto 0px;
		padding: 10px 0;
		background: #991188;
		color: #fff;
	}

	.dajianshi {
		margin: 5px auto 0;
		border: 1px solid #ccc;
		width: 980px;
		height: 490px;
		background-color: #eee;
	}
</style>

参考资料：
https://www.zhangxinxu.com/wordpress/2018/02/canvas-text-break-line-letter-spacing-vertical/

canvas基本属性

canvas基础方法