Hey, sorry I haven’t had time to look at this very closely yet.
I still think I would probably move this all to a custom unlit material since who knows what exactly the volume decal code is doing. But here is some low hanging fruit.
You use acos and atan2. You should try replacing with acosfast and atan2fast. See FastMath.usf for details. In most cases I have found, the fastmath functions work fine for volumetrics stuff but it can be hard to predict where precision issues show up.
Hey @RyanB,
No problem at all man! You’re a tech artist at Epic so I’d imagine you’re pretty busy. I’m happy for any time you can make for us on the forums here. 
Ohh so that was what you meant regarding a separate custom material! I was thinking that you meant a custom node in the Volume decal material, but was confused since that was what I was already doing.
That makes a bunch of sense. I’d have to write the raymarching code again, but whatever at least I’d have more control over it that way!
Also will replace those two functions. I think precision issues wouldn’t be a problem cause I don’t require super detailed results or anything. These are for gameplay usage (hopefully) and the player won’t ever be looking too closely at them.
I don’t suppose there are any plans to expand Volume decal functionality? It’s quite a cool piece of tech so I’d be interested to see more features added to it.
Unfortunately I do not think we have any plans to work on volume decals. They were just a free friday project by one of our engineers - Mittring - who left epic late last year. So far we haven’t found any practical ‘shippable’ uses of the volume decals in any products so there has not been much pressure internally to make them a fully supported feature. They are really fun to play with though. It is tricky since the shaders tend to be very expensive, and its easier to optimize these kinds of shaders on an individual basis when you have the full code per shader exposed.
Ah, shoot.
Ah well, they are a ton of fun to mess with, that’s true. Could serve as a testbed for volumetric methods before you write the full custom node material for them.
In any case Ryan, thanks a bunch man. Will post with more updates soon, and hopefully with a video that runs at a decent framerate!
on 4.18.3 nothing is showing up? does some settings change or do i need a different setup for the materials.or do i have to put some commands in to the console to make the volumetric decals work?
the Blend Mode need to be Translucent
and
There need to be and input for the normal (constant with z value 1 works fine)
sorry to bump, but I also don’t get anything to show up. whatever I try the volumetric decal is always fully invisible
I’m on 4.22
