window::pump_events called SDL_SyncWindow on every begin_frame. On X11, when the window's geometry is
not what SDL expects (Xvfb without a window manager; gamescope, which sizes windows itself) and nothing
is pending, it ends in SDL_Delay(10): 10 ms of every game frame on the game thread. The race's game
logic takes 13 to 17 ms a frame, so it ran at 38 game frames a second (slow motion: H1's "felt like
half speed" ran at 38.5 in its race). Mock, 1728 sysmem pipelined, demo race:
KARTFRAME_SYNC_WINDOW=1 (old) 38.1 game fps, 72.9 sets/s, 3.7 % late; new 59.8 game fps,
120.6 sets/s, 0.0 % late; menus 58.5 -> 60.7.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
