Minetest built with SDL conflicts with kwin_x11 compositing

[zmv7]

Minetest version

Minetest 5.9.0-dev-c63c05b (Linux)
Using LuaJIT 2.1.1713773202
Built by GCC 13.2
Running on Linux/6.8.7-arch1-2 x86_64
BUILD_TYPE=Release
RUN_IN_PLACE=0
USE_CURL=1
USE_GETTEXT=1
USE_SOUND=1
STATIC_SHAREDIR="/usr/local/share/minetest"
STATIC_LOCALEDIR="/usr/local/share/locale"

Irrlicht device

SDL

Operating system and version

Arch, Fedora 40, FreeBSD 14

CPU model

AMD Ryzen 5 5600

GPU model

RTX 4070 Super

Active renderer

OpenGL 4.6

Summary

Kwin's compositing turns off whenever minetest built with USE_SDL2=1 is running. It doesnt happen on USE_SDL2=0 builds. I reproduced it on Archlinux, Fedora 40(they're both with plasma6), FreeBSD 14 (latest repo branch, plasma5). Tried nouveau and proprietary nvidia drivers. Also reproduced in LXQt + kwin_x11.
Cannot reproduce in XFCE.

Steps to reproduce

1. Get OS with Plasma desktop
2. Compile minetest with USE_SDL2=1 flag
3. Launch minetest
4. Look for graphical issues in the desktop shell:
   • Wobbly windows, transparency, animations will not work
   • Windows above minetest will leave a trail when moving quickly
   • You can also try to launch picom, it should start successfully and will get killed by kwin once you close minetest window.

[rollerozxa]

Plasma/KWin automatically disables compositing on Xorg if programs request it to reduce latency, which SDL does. You need to disable "Allow applications to block compositing" in the KWin compositor settings if you don't want it to do that.

[zmv7]

Plasma/KWin automatically disables compositing on Xorg if programs request it to reduce latency, which SDL does. You need to disable "Allow applications to block compositing" in the KWin compositor settings if you don't want it to do that.

It works, however, shouldn't apps properly control it using SDL_SetHint? For example disable compositing in fullscreen mode only, etc?

[sfan5]

It appears SDL disables compositing by default: https://discourse.libsdl.org/t/why-is-compositing-disabled-on-normal-x11-windows/37712
We could add code to set the mentioned hint to tell SDL to keep it enabled, but the default behavior is not our fault.