You are amazing. Thanks so much, your info was very helpful :)
On Thursday, September 6, 2018 at 1:07:25 PM UTC-5, Treyten Carey wrote:
>
> Hi,
>
> This isn't necessarily an Emscripten issue but I thought this was a good
> place for this question since I need to call C from JavaScript through
> Emscripten.
>
> *What I'm trying to do:*
> The user should be able to select a WebGL button. The button calls an HTML
> input file which brings up File Explorer to select a file (such as a txt
> file or image). When the user selects a file (including a binary file), the
> contents get sent from JavaScript to C, where C then writes the file to the
> Emscripten local file system directory and where I should be able to send
> the contents of the file over C sockets (this is why I need to be able to
> get binary file contents, because I will be doing things with it in C).
>
> *What I've tried:*
> My HTML has an input element:
> <input id="file-input" type="file" name="name" style="display: none;"/>
>
> In my C code, when the user presses the WebGL button, I select the
> file-input element to open the file selection:
> emscripten_run_script(
> (char*)((std::string)
> "document.getElementById('file-input').click(); " +
> "var fileCont; " +
> "var reader = new FileReader(); " +
> "reader.onloadend = function(evt) { " +
> " if (evt.target.readyState == FileReader.DONE) { " +
> " fileCont = evt.target.result; " +
> " } " +
> " var arrayBuffer = this.result, " +
> " array = new Uint32Array(arrayBuffer), " +
> " binaryString = String.fromCharCode.apply(null, array); " +
> " Module.ccall('EM_gotOpenFileName', null, ['string', 'string',
> 'number'], [document.getElementById('file-input').value, binaryString,
> arrayBuffer.byteLength]); " +
> "}; " +
>
> "reader.readAsArrayBuffer(document.getElementById('file-input').files[0]); "
> ).c_str());
>
> Which then calls my C function where I do stuff with the file content:
> extern "C"
> {
> EMSCRIPTEN_KEEPALIVE void EM_gotOpenFileName(char* fileName, char*
> cont, int len)
> {
> // Store the file in a temporary location so we can read it later
> if we need to.
> // JavaScript doesn't allow us to grab it's location, so we must
> do it this way.
> std::string tempFile = fileName;
>
> // Getting the file's name without any directories. i.e
> "C:/fakepath/file.png" will turn into "file.png"
> std::vector<std::string> tkns = findTokens("/", tempFile);
> tempFile = tkns[tkns.size()-1];
> tkns = Operations::findTokens("\\", tempFile);
> tempFile = tkns[tkns.size()-1];
> tempFile = (std::string)".temp/" + tempFile;
>
> writeFile(tempFile, cont, len); // write the file. assume this
> works fine using fwrite.
>
> // ...
> }
> }
>
> *What's (not) working:*
> Text files are writing correctly and being transferred with no problems.
> Binary files, such as images, are not. The data written looks different
> than the actual file selected, though they have the same number of bytes.
> In JavaScript, I've tried using Uint8Array and Uint16Array. Uint32Array
> errors "Invalid offset/length when creating typed array", and Uint64Array
> doesn't exist.
>
> --
>
> Is there something I am doing wrong, or some other way I should read a
> file (like an image's) contents?
> I need to be able to load the data (including binary data from an image)
> into memory that I can do stuff with in C.
>
> Thanks,
>
>
>
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