ArrayBuffer到Blob的转换 [英] ArrayBuffer to blob conversion

问题描述

我有一个项目，需要在浏览器中显示djvu模式.

I have a project where I need to display djvu schemas in browser.

我在Github上找到了这个旧的库，据我了解，该库可以转换djvu文件到bmp，然后将其放入canvas元素.

I found this old library on Github which, as far as I understood, converts djvu files to bmp and then puts them into canvas element.

正如我所说，库是旧的(最后一次提交是在5年前)，因此我需要进行一些更正.主要问题是lib使用过时的BlobBuilder.

As I said, library is old(last commit was 5 years ago), so I need to make some corrections. Main problem is that lib uses obsolete BlobBuilder.

我为解决此问题而采取的步骤:

Steps I made to solve this problem:

1. 通过Chrome DevTools解压缩该库
2. 初始错误在第3774行var c = "undefined" != typeof MozBlobBuilder ? MozBlobBuilder : "undefined" != typeof WebKitBlobBuilder ? WebKitBlobBuilder : console.log("warning: cannot build blobs")
3. 我注释了这一行
4. 接下来，我也注释了c = new c;行以及以下几行.

1. Decompress this library via Chrome DevTools
2. Initial error is at line 3774 var c = "undefined" != typeof MozBlobBuilder ? MozBlobBuilder : "undefined" != typeof WebKitBlobBuilder ? WebKitBlobBuilder : console.log("warning: cannot build blobs")
3. I commented out this line
4. Next, I commented out line c = new c; and some of following lines too.

所以，现在看起来是这样(变量I是数组缓冲区，而ololo1和ololo2是某种偏移量和限制)

So, now it looks this way(variable I is array buffer, and ololo1 and ololo2 are some kind of offset and limit)

var c = new Blob(new Uint8Array(new Uint8Array(I,ololo1,ololo2)))
              , b = b.createObjectURL(c)
              , c = document.getElementById(kb)
              , f = c.getContext("2d")
              , h = new Image
              , g = a[Ea >> 2]
              , i = a[Fa >> 2]
              , j = c.width
              , k = Math.round(i * j / g);

            h.onload = function()
            {
                var a = g / j;
                4 < a && (a = 4);
                1 > a && (a = 1);
                f.globalAlpha = 1;

                for (N = 0; N < a; N++)
                    f.drawImage(h, N, N, g - a + N, i - a + N, 0, 0, j, k),
                    f.globalAlpha *= 1 - 1 / a;
                R(h.complete, "Image /bmp.bmp could not be decoded")
            }
            ;
            h.onerror = function(errorMsg, url, lineNumber, column, errorObj) {
                console.log(errorMsg, url, lineNumber, column, errorObj);
                console.log("Image /bmp.bmp could not be decoded!")
            }           
            ;

现在我停留在错误"Image/bmp.bmp无法解码！"(扔到h.onerror处理程序中).

And now I stuck at error "Image /bmp.bmp could not be decoded!"(throwed in h.onerror handler).

所以，我的问题是:我做错了什么?

So, my question is: what I am doing wrong?

推荐答案

我不知道作者为什么将他的Uint8Array包装在一个新的...中，请注意，我真的不知道这两个弃用的BlobBuilder API，但我在您的代码中看到的一个错字是您需要将TypedArray包装在普通的Array中:

I don't know why the author did wrap his Uint8Array in an new one... note that I don't really know either the deprecated BlobBuilder API, but one typo I can see in your code is that you need to wrap your TypedArray in a normal Array:

new Blob([new Uint8Array(buffer, byteOffset, length)]);

Blob构造函数将 blobParts序列作为第一个参数，然后搜索此序列中的 BufferSource ， USVStrings 和 Blob 元素.因此，当您传递 TypedArray 时，它将实际上遍历此 TypedArray 的所有条目，并将其视为 USVString (从而将其数值转换为数字).值( Blob 中的UTF-8字符串).那很少是您想要的，所以最好总是在此构造函数中传递一个 Array .

The Blob constructor takes a blobParts sequence as first parameter, and then searches for BufferSource, USVStrings and Blob elements in this sequence. So when you pass a TypedArray, it will actually iterate over all the entries of this TypedArray and treat these as USVString (and thus convert their numerical value to UTF-8 strings in the Blob). That's rarely what you want, so better always pass an Array in this constructor.

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