canvas设置图形各种混合模式，类似photoshop效果

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canvas如何设置图形各种混合模式呢？通过context.globalCompositeOperation = type的方法来实现。这里面的type有很多种。请参考列表。

示例效果图

type列表

示例源代码（共115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: 2024-02-04
*/
<template>
	<div class="djs_container">
		<div class="top">
			<h3>canvas设置图形各种混合模式</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('source-over')">source-over</el-button>
                <el-button type="primary" size="mini" @click="draw('source-in')">source-in</el-button>
				<el-button type="primary" size="mini" @click="draw('source-out')">source-out</el-button>
				<el-button type="primary" size="mini" @click="draw('source-atop')">source-atop</el-button>
				<el-button type="danger" size="mini" @click="draw('destination-over')">destination-over</el-button>
				<el-button type="danger" size="mini" @click="draw('destination-in')">destination-in</el-button>
				<el-button type="danger" size="mini" @click="draw('destination-out')">destination-out</el-button>
				<el-button type="danger" size="mini" @click="draw('destination-atop')">destination-atop</el-button>
				<el-button type="success" size="mini" @click="draw('lighter')">lighter</el-button>
				<el-button type="success" size="mini" @click="draw('copy')">copy</el-button>
				<el-button type="success" size="mini" @click="draw('xor')">xor</el-button>
				<el-button type="success" size="mini" @click="draw('multiply')">multiply</el-button>
				<el-button type="success" size="mini" @click="draw('screen')">screen</el-button>
				<el-button type="success" size="mini" @click="draw('overlay')">overlay</el-button>
				<el-button type="success" size="mini" @click="draw('darken')">darken</el-button>
				<el-button type="success" size="mini" @click="draw('lighten')">lighten</el-button>
				
				<el-button type="warning" size="mini" @click="draw('color-dodge')">color-dodge</el-button>
				<el-button type="warning" size="mini" @click="draw('color-burn')">color-burn</el-button>
				<el-button type="warning" size="mini" @click="draw('hard-light')">hard-light</el-button>
				<el-button type="warning" size="mini" @click="draw('soft-light')">soft-light</el-button>
				<el-button type="warning" size="mini" @click="draw('difference')">difference</el-button>
				<el-button type="warning" size="mini" @click="draw('exclusion')">exclusion</el-button>
				<el-button type="warning" size="mini" @click="draw('hue')">hue</el-button>
				<el-button type="warning" size="mini" @click="draw('saturation')">saturation</el-button>
				<el-button type="warning" size="mini" @click="draw('color')">color</el-button>
				<el-button type="warning" size="mini" @click="draw('luminosity')">luminosity</el-button>
			</h4>
		</div>
		<div class="dajianshi ">
			<canvas id="dajianshi" ref="mycanvas" width="980" height="410"></canvas>
		</div>
	</div>
</template>
<script>
	export default {
		data() {
			return {
				ctx: null,
				canvas: null,
				imageUrl: require('../assets/bg.png'), 
			}
		},
		mounted() {
			this.setCanvas()
		},
		methods: {
			clearCanvas() {				
				this.ctx.clearRect(-180, -50, this.canvas.width, this.canvas.height);
				this.ctx.restore();
			},
			setCanvas() {
				this.canvas = document.getElementById('dajianshi');
				if (!this.canvas.getContext) return;
				this.ctx = this.canvas.getContext("2d");
			},
			draw(type) {
				this.clearCanvas();
				this.ctx.save();
				this.ctx.translate(300,50);
				const image = new Image();
				image.src = this.imageUrl;
				image.addEventListener("load", () => {
					this.ctx.drawImage(image, 0, 0, 400, 350);					
					this.ctx.globalCompositeOperation = type
					this.rect(this.ctx,100,90,200,150,'blue')
				});
			},
			rect(ctx,x,y,w,h,fillcolor){
				ctx.fillStyle=fillcolor;
				ctx.fillRect(x,y,w,h)				
			},
			
		}
	}
</script>
<style scoped>
	.djs_container {
		width: 1000px;
		height: 680px;
		margin: 50px auto;
		border: 1px solid #222;
		position: relative;
	}

	.top {
		margin: 0 auto 0px;
		padding: 10px 0;
		background: #222;
		color: #fff;
	}

	.dajianshi {
		margin: 5px auto 0;
		border: 1px solid #cde;
		width: 980px;
		height: 410px;
	}
	
	.top>>>.el-button{ margin-bottom: 8px;}
</style>

canvas基本属性

canvas基础方法