Confused with framerate difference while prototyping

I’m building a open world. At the moment I’m prototyping and testing to see the best way to go about things to get the best framerate whilst making the game environment beautiful. I have a 5kmx5km map, I put the standard grass material from the starter content on it and added the grass node in the material. I was getting a solid 120 on the desktop and a solid 75 with the DK2.

Then I added a forest to see how far I put push for meshes and density. And I was able to get this with a solid 75fps in the DK2


And to get it bright and give the forest some life I added the butterfly from a Epic project and added a light on it and added a ground bug with a green light. Which looks beautiful in VR

The problem that is confusing me is I created a landscape layer material for the textures to be painted. Even down scaling the textures to 512px. On the desktop I am getting 80FPS while in the DK2 I am getting a solid 75FPS. I know what your going to say, “Your getting a solid 75fps don’t worry about it.”. But I can’t figure out why its doing it. can anyone tell me, why it is doing it. So I can understand the cause, and work to keep the performance in VR. Its done it in 4.12 and also with 4.13, and also disable dx11 and enabling Vulkan in 4.13 does the same.

Thanks if you help me understand why.

Hello seandennis,

VR is getting locked at 75 frames to keep it stable. Also the refresh rate is 75hz in the oculus so more then 75 frames you won’t see.
So if you have more then 75fps unreal or oculus restrict it to 75fps. If you have less then 75 but more then 45 fps so let’s say you have 70 fps unreal / oculus will lock it at 45 fps so that you wont get motion sickness and such things. The users eyes want a constant refresh rate on their eyes to prevent issues.

Stefan are you sure ? What about the whole 90+FPS average for submissions…im not that tech savvy though, so maybe I missed the point of your post

Ah sorry my bad the caps are 45 - 75 - 90 fps. so if you get 90 fps or higher it will stay at 90 fps because of the refresh rates of the VR devices are 90hz. so if you don’t get the 90fps in vr then it is still to heavy.
Did you change the fps cap in the project settings? maybe that helps a bit.

Thanks Stefan, for answering my question. So basically when developing for VR the idea is to keep the frames as high as possible, but try not to let the frame rate get less then 45 fps otherwise sim sickness will start effecting the user. I’ll keep that in mind when developing. Also if that is the case, would it be wise to enable smooth frame rate and set min to 45 fps and set max to 90 fps. At the moment I have fixed frame rate enabled at 90 fps.

You can enable smooth frame rate. But it is testing to see if it helps or not. :slight_smile: I have also tried it but I don’t see any diffrence so I like to put it off for less calculations.

Don’t set a fixed frame rate, if you fail to hit it then physics will be slowed down to and your gameplay will suffer in VR if anything relies on it (also looks bad to the user). Smoothed frame rate is also pretty much useless considering most VR platforms regulate frames themselves either with interleaving or time/space warp to make up for lost frames and smoothing either does nothing or gets in the way of it.

Also the DK2 had a lower refresh rate than new headsets, oculus requires 90fps because the CV1 is 90htz.

Thanks for your reply Stefan and Mordentral, I know the latest VR devices such as CV1, VIVE and OSVR use 90fps (90htz), I can’t afford the latest headset :frowning: , due to unemployment :(. I got my DK2 in Feb last year while work was good, So I work with what I have. I just watched a talk by John Carmack. He said in his talk that, even though you may downscale your textures, a DXT type texture is more bites to the memory and causes slower frame rates. For VR a lower Bit type texture needs to be used. That is the thing, that I noticed with a open world and painting the landscape with different layers. At the moment all my landscape textures are TGA with alpha at 512px and I have only bump maps on textures that will be noticed and aren’t covered by something. So I may try exporting textures from photoshop in a different format to without alpha to see any performance benefits. Its all trial and error, but I don’t want to lower eye candy and a beautiful experience. I am willing to sacrifice a few meshes or cut a few more tries if needed to keep my idea of what experience I want to produce. considering my test map is 5kmx5km but my actual game map at this stage is 20kmx20km level streamed.