What's the laundry pattern?

Choose it from the ‘example’ select box and see for yourself ;)

OK, thanks! I found it.

But why would vsync make that hard? You mean if it's 1:1 on the vsync?

I guess the idea is was that Firedancer is designed with fixed update rate in mind. And the demo makes an assumption that it will run at 60 FPS = 60 updates per second, probably becoming very fast and hard on 360 Hz screens. But that's just nitpicking on details in library demo. It would be bad to have such mistake in a real game or game engine demo, but it's not that surprising for example code to skip details for the sake of simplicity. The main purpose of example is demonstrating the library as cleanly as possible without distracting reader by containing more boiler plate code for third party game engine than the thing it's attempting to demonstrate. I don't see a reason why you couldn't update FireDancer VM at whatever fixed rate you want (faster or slower than typical FPS) just like many games and game engines with fixed tick rate for physics or game logic handle it.

If the shots weren't timed to a regular fixed clock, then there would be visual jitter in the pattern. Even if you correctly spawn shots in between two ticks, each bullet would only first appear some random distance along its trajectory.

If an enemy spawns e.g. a circle of bullets, you would see it rapidly expanding/contracting.

I suspect a variable frame rate bullet hell game would be harder to play, but I'm not a fan of the genre.

You could probably make a difference between physics frames and visual frames?

Games like Quake 3 do that, I think.

Check out the "static geometric" pattern too while you're at it, there's a zooming out optical illusion occurring there

Laundry looks easy! Just move slightly to the left from bottom center to the safe zone. And speaking of safe zones, so many frameworks miss the opportunity to visualize them, calling for Ice Sign "Icicle Fail" in almost every geometric shmup.