canvas使用跨域的图片时，image.crossOrigin = 'Anonymous'，Tainted canvases may not be exported？

Question

canvas使用跨域的图片时，不加 image.crossOrigin = 'Anonymous'; 图片可以绘制，但是不能调用 toBlob(), toDataURL() 或 getImageData() 方法，调用它们会抛出安全错误。

Unable to get data URL. Failed to execute ‘toDataURL’ on ‘HTMLCanvasElement’: Tainted canvases may not be exported.

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如果加上 image.crossOrigin = 'Anonymous'; 报错 Access to image at 'http://10.10.10.112/product/AVWT-154FESSA.png' from origin 'http://localhost:8080' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

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问题的原因：是后端没有配置允许接受跨域

Answer 1

换下小写试试

image.setAttribute(‘crossorgin’,’anonymous’)

将image作为文件读取blob流,ctx.toBlob 试试

export function imageToFileByCanvas(image: HTMLImageElement, fileName: string = "image.jpg"): Promise<File> {
    const canvas = document.createElement("canvas")
    canvas.width = image.width
    canvas.height = image.height

    const ctx = canvas.getContext("2d")!
    ctx.drawImage(image, 0, 0)

    return new Promise(resolve => canvas.toBlob(blob => resolve(new File([blob!], fileName))))
}

async function getImage(){
      const file = await imageToFileByCanvas(image, "image.jpg")
    const imgUrl = URL.createObjectURL(file) // image 内存地址
}

export function imageToFileByBlob(image: HTMLImageElement, fileName: string = "image.jpg") {
    const binStr = atob(image.src.split(",")[1])
    const len = binStr.length
    const arr = new Uint8Array(len)
    for (let i = 0; i < len; i++) {
        arr[i] = binStr.charCodeAt(i)
    }

    const blob = new Blob([arr], { type: "image/png" })
    return new File([blob], fileName)
}

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