r/kde • u/FrameXX • Aug 30 '26

General Bug Window resizing - Filelight VS Dolphin

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u/Trapped-In-Dreams Aug 30 '26

Well, yeah, I meant to say that desync is worse in qml apps (because of their multi-threaded GPU-accelerated architecture). Also you can speed them up a little by setting env QSG_NO_VSYNC=1

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u/grekand46 Aug 30 '26 edited Aug 30 '26

That actually worked super well.
Edit: I looked a bit into Qt's source code (not as bad of an experience as I thought it would be) and found that setting QSG_NO_VSYNC to 1 causes the surface format to have a swap interval of 0 as opposed to the default value of 1. When nonblocking buffer swaps are available and the surface has a nonzero swap interval, Qt would set the actual EGL swap interval to 0, which makes eglSwapBuffers nonblocking, and emulate the block itself while taking Wayland frame callbacks into consideration. This appears pretty reasonable to me, but clearly something isn't working properly. I suspect there's some sort of double throttling going on since there aren't any excessive rendering operations even without the emulated blocking. (side note: QSG_NO_VSYNC is kind of a misnomer in Wayland due to vsync always being present)