生成二位码，位于背景图的位置

写了个例子，可以隐藏canvas 生成的二维码，用image 标签控制在哪里显示

<template>  
    <view>  
        <view class="">  
            canvas  
        </view>  
        <image class="qr-img" :src="qrcodeSrc" v-if="qrcodeSrc"  ></image>  
        <canvas id="qrcode" class="qrcode-class" canvas-id="qrcode"></canvas>  
    </view>  
</template>  

<script>  
    import uQRCode from '@/common/js/uqrcode.js'  

    let _this;  
    export default {  
        data(){  
            return {  
                qrcodeSrc:''  
            }  
        },  
        onLoad() {  
            _this = this  
            this.make()  
        },  
        methods: {  
            make() {  
                uni.showLoading()  
                uQRCode.make({  
                    canvasId: 'qrcode',  
                    text: '123456',//二维码内容  
                    size: 150,  
                    margin: 10,  
                    backgroundColor: '#ffffff',  
                    foregroundColor: '#000000',  
                    fileType: 'jpg',  
                    correctLevel: uQRCode.defaults.correctLevel,  
                    success: res => {  
                        _this.qrcodeSrc = res;  
                        uni.hideLoading()  
                    },  
                    fail:err=>{  
                    }  
                })  
            }  
        }  
    }  
</script>  

<style scoped lang="scss">  
    .qrcode-class{  
        z-index: -999;  
    }  
</style>