uni-app uni.canvasToTempFilePath ios app端返回的图片为空白

uni-app uni.canvasToTempFilePath ios app端返回的图片为空白 产品分类： uniapp/App

bug描述：

H5、安卓都能正常执行，ios端执行canvasToTempFilePath方法返回的图片路径为空白

示例代码：

<canvas id="canvas" :style="{width:canvas_width+'px' ,height:canvas_height+'px' }" canvas-id="firstCanvas" ></canvas>
// 照片打水印
imageWatermark (url, canvas_id, width = 100, height = 100,content1,content2,self) {
return new Promise((resolve, reject) => {
/*加上延迟 处理h5 防止为改变dome 大小就开始绘制 会出现图片显示不完整*/
setTimeout(()=>{
const ctx = uni.createCanvasContext(canvas_id, self);
ctx.drawImage(url, 0, 0, width, height );
ctx.setFontSize(50)
ctx.setFillStyle('#ff0000')    //水印颜色
let clientIdWidth = 10
let clientIdHeight = 50    //内容2高度
ctx.fillText(content2, clientIdWidth, clientIdHeight)
&nbsp; &nbsp; &nbsp; &nbsp; for(let i = 1; (i-1)*20 < content1.length; i++){
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; let start = 18*(i-1);
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; let end = 18*i;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ctx.fillText(content1.substring(start, end), 10, (50+50*i))
&nbsp; &nbsp; &nbsp; &nbsp; }  

            ctx.draw(false, () => {  
                setTimeout(() => {  
                    uni.canvasToTempFilePath({  
                        canvasId: canvas_id,  
                        destWidth:width,  
                        destHeight:height,   
                        fileType: 'jpg',  
                        quality: 0.9,  
                        success: (res) => {  
                            console.log(res)  
                            resolve(res.tempFilePath)  
                        },  
                        fail: (err) => {  
                            console.log(err,123)  
                        }  
                    }, self)  
                },500)  

            })  
        },500)  

    })  

},