I was reading unreal engine 5.4’s release notes and it mentioned that on mobile when GPU scene is enabled, UBOs will be used. It mentioned that if UBO support is not present it will fall back on using the PC GPU scene.
I wanted to know what the performance implications of not using UBOs would be on mobile such that the PC GPU scene is used.
It will render an empty scene basically. For example in my case with android 10 vulkan version 1.1.87 it just skips all geometry and scene appears empty with only light being visible. Even though it shows that it renders something in stat unit by drawcalls. Btw GPU scene never worked well. Many of my fellow game developers of mobile games mentioned that they had to disable it due to insane number of crashes from production related to it.
Fyi it seems to only work fine only for the most recent android devices and maybe iphone 16
Yes, when using the GPU scene I noticed that static mesh objects were not rendered correctly(Instanced objects seem fine).
Using RDC I found that a cube which should be rendered in front of the camera was being rendered behind it. It seems that it’s not the GPU scene that is the problem it is the UBO usage that causes this issue. That’s why I asked this question, why use UBOs in the first place if they screw up the render. What performance benefit do they provide?
Also I am testing on an S23 running android 14 with VK 1.3.128
GPU scenes reduce CPU usage, so the CPU can be used for other things (like physics) and/or sleep more and consume less battery.
Mobile devices/chipsets are notorious for being much buggier than their desktop counterparts, so I would expect all mobile support features to be for experimentation for the first two years, and only turn it on for a release game after there’s broad market compatibility. Also, if I can test on specific devices with specific minimum OS versions, maybe I could have a device whitelist for popular, well supported devices, where I know it will work. That optimization of course takes labor for testing and support, so I’d have to profile the game to make sure it’s worth it before I committed to that.
