canvasToTempFilePath 失败 {errMsg: "canvasToTempFilePath:fail fail canvas is empty"}

微信官方文档中标明 canvas当使用2d时不用传参 canvasId，直接传入canvas实例即可。
参考文档：https://developers.weixin.qq.com/miniprogram/dev/api/canvas/wx.canvasToTempFilePath.html
改变下写法即可 参考下方示例

<template>  
    <view>  
        <button @tap="handleclick">canvas</button>  
        <image :src="imageSrc" mode="widthFix"></image>  
    </view>  
</template>  

<script setup>  
    import {  
        ref  
    } from 'vue'  
    const imageSrc = ref()  
    const handleclick = async () => {  
        // 创建离屏 2D canvas 实例  
        const canvas = wx.createOffscreenCanvas({  
            type: '2d',  
            width: 300,  
            height: 300  
        })  
        // 获取 context。注意这里必须要与创建时的 type 一致  
        const context = canvas.getContext('2d')  
        // 创建一个图片  
        const image = canvas.createImage()  
        // 等待图片加载  
        await new Promise(resolve => {  
            image.onload = resolve  
            image.src = "https://img-cdn-aliyun.dcloud.net.cn/guide/uniapp/app_download.png" // 要加载的图片 url  
        })  
        // 把图片画到离屏 canvas 上  
        context.clearRect(0, 0, 300, 300)  
        context.drawImage(image, 0, 0, 300, 300)  
        // 获取画完后的数据  
        uni.canvasToTempFilePath({  
            canvas: canvas,  
            success: (info) => {  
                imageSrc.value = info.tempFilePath  
            }  
        })  

    }  
</script>  

<style lang="scss">  

</style>