id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
24585	JOSM is running with low FPS on 4K screens.	anonymous	anonymous	"I’m running JOSM on my Mac Studio M3 Ultra, 96GB RAM, tons of CPU cores, latest JOSM from homebrew, latest MacOS on a 4K 240hz screen. 

But JOSM is just running slow, making it barely usable for me. I had the same experience before on Windows 10 with 48GB RAM on a Ryzen 2600, same 4k 240hz screen.

Here are some example videos
https://youtu.be/FpDl-ma0AOs
https://youtu.be/vvaKYz047O0

Related discussion: https://community.openstreetmap.org/t/josm-very-low-fps-on-4k-screens/140048

I see that JOSM is using a merely 3gb of RAM.

Based on the behavior that higher resolutions get slower, I assume that some calculation is exponential and I run into single core performance limitations.

Just moving around the end of a new line makes the CPU load go to 100%+. 
When I remove all downloaded data, the new line still consumes 100%+ CPU, but at least it's nearly smooth. I'm only downloading a small Zurich area, nothing insane, 150x150m. 


"	defect	closed	normal		Core bugreport	latest	needinfo