Is there a baked in engine frame rate limit of 1000 fps?

Community Community & Industry Discussion
1

Hello, this will likely strike most people as quite odd. I’m curious if UE4 has an internal frame rate cap. Out of sheer curiosity I’ve been experimenting with different renderers and engines and how fast they can render a self emissive cube with no lighting. I’ve written raw Open GL, Unity (with the three render modes), and now Unreal projects just with a simple emissive cube. I plan to make a vulkan and DX11 / 12 cubes from scratch as well to test but haven’t had time to get through the crazy amount of Vulkan boilerplate required.

What I’ve found though is UE4 seems to bounce around the 1000 fps (or 1ms frame time) mark pretty reliably. I’m trying it first with the forward renderer and I’ll also switch the project to deferred rendering to measure there.

However, the GPU and CPU do not seem particularly taxed (maybe 30% and 45% usage respectively) when I do this. In Unity comparatively I get around 2500 fps and the whole computer spins up like crazy (and I can hear pretty impressive coil whine from my GPU).

If such a limit exists does anyone know of a way to bypass it?

To be clear: I’m not suggesting such a limit (should it exist) is a real world problem as an actual game running at 1000 fps would be a pipe dream. None the less, if anyone knows if bypassing it is possible I would love to hear from you. !

2

You can adjust the fps cap using this command in the console.

t.MaxFPS 240 (or the number you want)

On a simple project with a cube and the first person controller, I set max fps to something high (1200) but I am capping out around 600 fps.

Note that Unreal has a lot of things going on in the background of the engine. I know you can make a Vulkan or OpenGL app and get like 3000 fps w/ a cube, but that is deceiving. A lot of the processing overhead in UE4 is fixed (for example the post-processing and requirements for deferred shading) so while a cube may “only” get 600 fps, adding a whole city and animated characters will not be a huge burden. Even with a pretty large city scene and a flying camera, I can still get around 120 fps, which is decent enough to ship a game.