Compile XaoS for the web via Qt

[kovzol]

On Feb 6 I managed to compile XaoS as recommended at
https://wiki.qt.io/Building_Qt_5_from_Git
https://wiki.qt.io/Qt_for_WebAssembly
https://doc.qt.io/qt-5/wasm.html
Both Firefox and Chrome is freezing on the startup:

But after a few seconds when Firefox asks if the process should be stopped, the init screen of XaoS is shown properly (interaction and running is however not possible):

This is very promising for the first attempt, I think we will be able to run XaoS in the browser in a reasonable time.

More info added later:
Some update... Meanwhile I learned that Qt can be compiled as pthread-capable and non-pthread-capable. The second one is the default. Unfortunately, Firefox no longer supports the first one out-of-the-box, but Chrome does. But I think we can disable thread support by removing USE_PTHREADS for the WebAssembly build.

Actually I still have no luck in making XaoS run in a browser, and thread handling is not the problem. It is clear that the main loop in MainWindow::eventLoop() is working, but for some reason the canvas will be actually never drawn. Only Firefox draws the final state of the canvas after I force the main loop to stop (when Firefox asks me to do that because the app is not responding). I assume that this kind of loop is incompatible with the WebAssembly approach, but not completely sure yet.

At https://github.com/msorvig/qt-webassembly-examples/tree/master/gui_opengl there is a quite minimal example that properly works in my Linux natively and also with the browser... I am afraid that the solution we currently use in XaoS is not supported in a browser at all---making an infinite loop with for(;;) is something that kills the browser resources since it is something synchronous. I guess we may need to think in asynchronous events.

JB's response:

Yes, I think that the event loop needs to be redone the Qt way. I was planning to do that anyway at some point but was going to wait until after 4.0. I think that probably the right way to do it for XaoS is to use a QTimer to fire periodically and call the UIH functions to update the fractal.

[szhorvat]

I just saw the new release with WebAssembly support. Are you hosting an online version on the XaoS website somewhere, and if not, would you consider doing so? This would be immensely useful for teaching.

[kovzol]

Yes, it's at https://matek.hu/zoltan/xaos. Feel free to use it, it is planned to be there permanently.