The plugin still steps at its own 25 fps, frame for frame; between frames
the turn continues, textures crossfade, and the cone follows a preview of
the newest audio, so beats land a refresh sooner. The big window replays
the original's GL calls through OpenGL (QPainter took ~40 ms a frame at
1080p); without GL it falls back. Gray mode is only the gray-mode colour on
the panel background. The sync slider goes to -50 ms (sooner).
