...and 1 minute later I found the problem by mulling over the ccall source
in preamble.js :D
The problem is that I'm passing a raw ArrayBuffer object, when ccall
expects an Uint8Array. ArrayBuffer has no .length property, which is
expected by ccall.
So the JS side needs to look something like this:
var content = new Uint8Array(loadEvent.target.result);
Module.ccall('emsc_pass_data',
null,
['string', 'array', 'number'],
[file.name, content, content.length]);
...some more examples in the docs and probably a test for ccall with
'array' would be nice though ;)
Cheers,
-Floh.
Am Mittwoch, 14. Dezember 2016 17:01:45 UTC+1 schrieb Floh:
>
> Hi,
>
> I can't seem to find example code of how to pass an ArrayBuffer from JS to
> C via ccall() (for instance, there doesn't seem to be a test for this in
> the SDK?), and I have problems doing this (the passed data is broken). I'm
> sure it's something simple...
>
> Background: I want to pass file content data from a JS drag-n-drop event
> handler to the C side.
>
> What I have on the JS side:
>
>
...
> // this is the array buffer as result of a FileReader, this contains the
> // expected data (I checked through logging the first couple of bytes to
> the console)
> var content = loadEvent.target.result;
>
> // now the ccall to a C function "emsc_pass_data" with 3 params, a string
> name, the content, and the length
> Module.ccall('emsc_pass_data',
> null,
> ['string', 'array', 'number'],
> [file.name, content, content.byteLength]);
> ...
>
> ...and on the C side I have:
>
> void emsc_pass_data(const char* name, const uint8_t* data, int size) {
>
> }
>
> The function is called, name has a valid string, size is also right, data
> is some pointer, but the pointed-to data behind the pointers doesn't match
> the ArrayBuffer content (it looks fairly random with lots of zeros).
>
> What am I doing wrong? I would most appreciate some code example to look
> at :)
>
> PS: the emscripten documentation on ccall is a bit hand-wavy on the array
> type, a small code example there would be very helpful (both the JS and C
> side), see here:
> https://kripken.github.io/emscripten-site/docs/api_reference/preamble.js.html#calling-compiled-c-functions-from-javascript
>
> Cheers,
> -Floh.
>
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