canvas实现二维码和图片合成的示例代码canvas 下载二维码和图片加水印的方法

import React, { Component } from 'react'
const qrcode = require('jr-qrcode')
const loadImg = (src) => {
    const paths = Array.isArray(src) ? src : [src];
    const promise = [];
    paths.forEach((path) => {
        promise.push(new Promise((resolve, reject) => {
            let img = new Image();
            img.crossOrigin = "Anonymous";
            img.src = path;
            img.onload = () => {
                resolve(img);
            };
            img.onerror = (err) => {
                console.log('图片加载失败')
            }
        }))
    });
    return Promise.all(promise);

}
const getImageData = (url, src) => {
    const imgsrc = qrcode.getQrBase64(url)
    let canvas = document.createElement('canvas')
    const width = document.documentElement.clientWidth
    const height = document.documentElement.clientHeight
    canvas.width = width*2
    canvas.height = height*2
    let ctx = canvas.getContext("2d")
     loadImg([imgsrc, src]).then(([img1, img2]) => {
        ctx.drawImage(img2, 0, 0, width*2, height*2)
        ctx.drawImage(img1, width-80, height*2-220, 200, 160)
        ctx.fillStyle = 'rgba(0,0,0,0.3)';
        ctx.fillRect(width-80, height*2-60, 200, 40);
        ctx.save()
        ctx.font="28px Arial"
        ctx.fillStyle = '#fff';
        ctx.fillText('长按识别二维码', width-80, height*2-30, 200, 160)
        let imageURL = canvas.toDataURL("image/png")
        document.getElementById('mix_img').setAttribute('src',imageURL)
    })
}
export default class QRcode extends Component {
    render() {
        const { url , picSrc} = this.props
        getImageData(url,picSrc)
        return (
            

                
            
        )
    }

}