Building Qt Apps to Wasm

lorn.potter · wrote on 5 Nov 2019, 22:43

You can either put the resulting .js, .wasm, .html files on a web server, or emscripten comes with emrun which will start a server and open the html file in a browser.

DragonOsman · wrote on 5 Nov 2019, 22:49

Thanks, I'll try that.

DragonOsman · wrote on 6 Nov 2019, 11:02

I launched Python's web server by running python -m http.server, but I get the same exact HTML page as before when I go to notepad.html. It still has that same error on it.

DragonOsman · 6 Nov 2019, 20:52

I get the exact same result with emrun. The error "TypeError: Body has already been read". How do I fix this? Someone please help. This seems like a JavaScript error so maybe I should also consult the Emscripten developers. But it's also something related to Qt and there may be something I need to know about how to run a Wasm module compiled from Qt code.

lorn.potter · wrote on 6 Nov 2019, 20:52

@DragonOsman said in Building Qt Apps to Wasm:

The error "TypeError: Body has already been read". How do I fix this?

I have seen that when I configure qt for threads and have forgotten to enable shared memory in the browsers.

Chrome: chrome://flags "WebAssembly threads support"
FireFox: about:config "javascript.options.shared_memory"

DragonOsman · 6 Nov 2019, 21:01

Okay, thanks. I'll have to see how to do that for MS Edge. Thanks for the info on Chrome.

lorn.potter · wrote on 6 Nov 2019, 21:01

@DragonOsman https://wiki.qt.io/Qt_for_WebAssembly

lorn.potter · wrote on 6 Nov 2019, 21:13

@DragonOsman said in Building Qt Apps to Wasm:

Okay, thanks. I'll have to see how to do that for MS Edge. Thanks for the info on Chrome.

I do not think Edge has re-enabled shared memory:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer

DragonOsman · 11 Jun 2019, 22:03

I used it in Chrome. The functionality of saving a file doesn't seem to work (may need to let WebAssembly use the filesystem) and the "Select Font" feature is giving me trouble. It opens up two dialogue boxes so I have cancel the second one. On the first one then, the font size selector goes crazy when I try to use it; it keeps going between different sets of two options in really fast succession and I can't choose one at all. Is there a special way to get the Notepad example to work as a Wasm app? These problems only appear in the Wasm app.

steno · 10 Jan 2020, 20:35

@DragonOsman said in Building Qt Apps to Wasm:

This is the error I get now when using prebuilt Qt to build the Notepad project:

wasm-ld: error: notepad.obj: machine type must be wasm32
wasm-ld: error: notepad.js_plugin_import.obj: machine type must be wasm32
wasm-ld: error: moc_notepad.obj: machine type must be wasm32
wasm-ld: error: qapplication.obj: machine type must be wasm32
wasm-ld: error: qwidget.obj: machine type must be wasm32
wasm-ld: error: qwasmlocalfileaccess.obj: machine type must be wasm32
shared:ERROR: 'C:/emsdk/upstream/bin\wasm-ld.exe -o c:\users\osman\appdata\local\temp\emscripten_temp\notepad.wasm --allow-undefined --lto-O0 main.obj notepad.obj -LC:\emsdk\upstream\emscripten\system\local\lib notepad.js_plugin_import.obj -LC:\emsdk\upstream\emscripten\system\lib moc_notepad.obj -LC:\Users\Osman\.emscripten_cache\wasm-obj C:/Qt/5.13.1/wasm_32/plugins/platforms/libqwasm.a C:/Qt/5.13.1/wasm_32/lib/libQt5EventDispatcherSupport.a C:/Qt/5.13.1/wasm_32/lib/libQt5FontDatabaseSupport.a C:/Qt/5.13.1/wasm_32/lib/libqtfreetype.a C:/Qt/5.13.1/wasm_32/lib/libQt5EglSupport.a C:/Qt/5.13.1/wasm_32/plugins/imageformats/libqgif.a C:/Qt/5.13.1/wasm_32/plugins/imageformats/libqicns.a C:/Qt/5.13.1/wasm_32/plugins/imageformats/libqico.a C:/Qt/5.13.1/wasm_32/plugins/imageformats/libqjpeg.a C:/Qt/5.13.1/wasm_32/plugins/imageformats/libqtga.a C:/Qt/5.13.1/wasm_32/plugins/imageformats/libqtiff.a C:/Qt/5.13.1/wasm_32/plugins/imageformats/libqwbmp.a C:/Qt/5.13.1/wasm_32/plugins/imageformats/libqwebp.a C:/Qt/5.13.1/wasm_32/lib/libQt5PrintSupport.a C:/Qt/5.13.1/wasm_32/lib/libQt5Widgets.a C:/Qt/5.13.1/wasm_32/lib/libQt5Gui.a C:/Qt/5.13.1/wasm_32/lib/libqtlibpng.a C:/Qt/5.13.1/wasm_32/lib/libqtharfbuzz.a C:/Qt/5.13.1/wasm_32/lib/libQt5Core.a C:/Qt/5.13.1/wasm_32/lib/libqtpcre2.a C:\Users\Osman\.emscripten_cache\wasm-obj\libc.a C:\Users\Osman\.emscripten_cache\wasm-obj\libcompiler_rt.a C:\Users\Osman\.emscripten_cache\wasm-obj\libc-wasm.a C:\Users\Osman\.emscripten_cache\wasm-obj\libc++-noexcept.a C:\Users\Osman\.emscripten_cache\wasm-obj\libc++abi-noexcept.a --whole-archive C:\Users\Osman\.emscripten_cache\wasm-obj\libembind-rtti.a --no-whole-archive C:\Users\Osman\.emscripten_cache\wasm-obj\libgl-webgl2.a C:\Users\Osman\.emscripten_cache\wasm-obj\libdlmalloc.a C:\Users\Osman\.emscripten_cache\wasm-obj\libpthread_stub.a C:\Users\Osman\.emscripten_cache\wasm-obj\libc_rt_wasm.a --import-memory --import-table -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --export __wasm_call_ctors --export __data_end --export main --export malloc --export free --export setThrew --export __errno_location --export fflush --export _ZSt18uncaught_exceptionv --export __cxa_find_matching_catch --export __cxa_is_pointer_type --export __cxa_can_catch --export emscripten_GetProcAddress --export emscripten_webgl_make_context_current --export emscripten_webgl_get_current_context --export strstr --export emscripten_builtin_memalign --export memalign --export emscripten_builtin_free --export _get_environ --export realloc --export _get_tzname --export _get_daylight --export _get_timezone --export strlen -z stack-size=5242880 --initial-memory=16777216 --no-entry --global-base=1024' failed (1)

If I pass -device-option WASM_OBJECT_FILES=1 to Qt configure when building Qt, will that fix this?

I checked notepad.obj and notepad.js_plugin_import.obj with wasm-dis.exe before and found that they were Wasm object files. But now when I check again, main.obj does have Wasm code in it but this is what I get for notepad.obj:

[parse exception: surprising value (at 0:4)]
Fatal: error in parsing wasm binary

All three of the ones from my code give the same error. How can I find those three object files from the Qt library so I can check them too?

What was your solution for machine type must be wasm32? I have been seeing this as well.

lorn.potter · S steno 9 Dec 2019, 19:16

@steno said in Building Qt Apps to Wasm:

What was your solution for machine type must be wasm32? I have been seeing this as well.

If you use the prebuilt binaries, you need to use emscripten version 1.38.27 or 1.38.30 for threaded.

./emsdk install sdk-fastcomp-1.38.27-64bit
./emsdk activate sdk-fastcomp-1.38.27-64bit