Hapax, just wanted to comment on here and say thanks for all of your help with this stuff. I've used Kairos on my last couple of projects, and it has made such a huge difference! I'm on a Macbook Pro, and even then, I noticed that the game would also stutter, especially when listening to music on YouTube in the background. What fixed the stuttering on my end was adding setVerticalSyncEnabled to the window. Movement is now smooth—even while running YouTube!
Just adding my experience here in case it helps anyone else in the future. If anyone else wants more details, especially for those on Mac, do let me know and I'll add those here.
