Performance with trees at close distance

Does anyone else see their frame time go up far more than expected when viewing trees close up? For me, I’ve no problem with thousands of billboarded trees, or a good number of trees without LOD but at a further distance (say > 10m). But as soon as I get within a close distance of a few, the frame time goes up dramatically. This is in VR of course. In desktop mode, the frame time hardly goes up even with a lot of nearby trees.

It doesn’t appear to be related to tricount or draw calls, as even with significantly lower of both I’ve still seen my frames go up significantly when getting close to several trees. I’ve also tried to simplify the tree materials, and use more low-poly models, to no avail. I suppose it’s overdraw that could be doing it? Regardless, I’d like to hear from some others who have tried using trees in VR, maybe it’s just me who’s experiencing this.

Here’s my setup for reference:
Rift S
GTX 1060, Ryzen 2600x, 16GB of RAM
UE 4.26 with forward rendering

You should enable early z pass with mask material in rendering option. It will be a huge boost if your problem is overdraw.

Thank you for the suggestion, but I already did that and it made a minor difference if any.

I’ve done some more tests, with smaller groups of trees spaced farther apart, and the performance isn’t as bad as I thought. With shorter ones it does get real bad up close, as shown below.


I suppose it makes sense considering how much of the screen the leaves take up. I tested some simple overlapping translucent materials and it results in the same thing. It’s still a bit surprising because there’s no noticeable difference in desktop, but a 50%+ increase in render time for VR. It must be very sensitive to overdraw I guess. Maybe I’ll try making leaves with very fine outlines at LOD0.​