At least I was a bit confused by that sentence in the docs ;) I was thinking that on the JS side, data goes in as normal JS arrays (that is clear enough), but I interpreted the 'typed array' as a generic ArrayBuffer object, and thought that the note about 8-bit arrays is about how the data arrives on the C side (as an array of bytes, regardless of what type the items in the ArrayBuffer are).
I think it would be better if the docs mention the JS class name Uint8Array somewhere (and of course a small code sample would be even better). Am Mittwoch, 14. Dezember 2016 19:52:58 UTC+1 schrieb Alon Zakai: > > Adding an assert and a typed array test in > https://github.com/kripken/emscripten/pull/4797 > > As for the docs, they say > > > use ``"number"`` for any C pointer, and ``"array"`` for JavaScript > arrays and typed arrays; note that arrays are 8-bit > > is that not clear enough? > > On Wed, Dec 14, 2016 at 8:14 AM, Floh <[email protected] <javascript:>> > wrote: > >> ...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. >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "emscripten-discuss" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected] <javascript:>. >> For more options, visit https://groups.google.com/d/optout. >> > > -- You received this message because you are subscribed to the Google Groups "emscripten-discuss" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
