Pyodide with SDL2 support.

[km19809]

Hello.
I want to show a (WIP) work that uses pyodide and SDL2.
Here is one of the demo

It runs pyxel, which is one of the greatest python 2D game engines.
Although the porting was not finished yet, I want to share the result here.
Without the support from the contributors of pyodide, I was not able to port them. (Of course, thanks to participants of kitao/pyxel#354 !)

Its main differences from the original are:

1. It was Linked with SDL2. (TypeError: getWasmTableEntry(...) is not a function #2964 (comment))
2. It detects canvas automatically, by modifying pre.js
3. It uses the pre-released version of SDL2, to solve the audio buffer problem. (Audio: How does Emscripten calculate its spec? libsdl-org/SDL#6060)

Of course, there are some weird behaviors (especially related to the mouse).
Also, other SDL2 packages are not tested (ex: Pygame, PySDL2; They need additional libs such as SDL2_TTF).
But I'm glad that I can share my experience.

It will be great if pyodide support SDL2 officially.
(At least, provide a version with SDL2 support. It makes compiled binary larger, so it loads slow.)

Here's my fork:
github

[ryanking13]

Thanks for sharing your work @km19809. Are you using SDL2 port that emscripten provides or did you build SDL2 by userself? I think the emscripten version of SDL2 was a bit old.

It will be great if pyodide support SDL2 officially.

Should SDL2 need to be linked to the Pyodide main module?

[ryanking13]

Yes, without it, the emscripten does not generate SDL-related code. (#2964 (comment))

because only main module has system libraries linked in

I think Pyodide is working pretty well with linking libraries to side modules, but, I don't know, maybe SDL2 can be an exception.
How does the size of pyodide.asm.wasm changes when you link SDL2 to the main module?

[km19809]

Before:

wasm 3.0MB, data 3.2MB, asm.js 278kB
After:

wasm 9.6MB, data 5.1MB, asm.js 1.8MB

At least 10MB larger. I think there is something that I missed (especially optimization).

[ryanking13]

In main, the size of pyodide.asm.wasm is around 8MB, maybe you detached some libraries from the main module?

[ryanking13]

because only main module has system libraries linked in

I think Pyodide is working pretty well with linking libraries to side modules

I suspect emscripten-core/emscripten#17675 this was the reason why SDL2 was not working correctly when linked to the side modules.

[hoodmane]

I think there is also the more fundamental problem that SDL2 includes JavaScript code, and the dynamic linking model does not currently support JavaScript in side modules.