Loading
The page opens on a loading screen carrying the game's name, a bar, and a line naming the work in hand - building the scene, generating the world, rolling out the aircraft, calibrating the instruments, and drawing the first frame. The screen fades off on the strength of a frame the renderer has actually drawn rather than on a timer, so it is gone exactly when there is a world behind it and not a moment before.
Start-up runs in one pass with no chance for the browser to paint between the steps, so the bar is not seen creeping from one to the next: it is a width the stylesheet animates toward, and the progress behind it is real whether or not every step of it gets a frame of its own.