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Volume decals

Okay, so I’ve read the release notes of 4.9, but I haven’t tried it yet since I’m a bit busy at the moment, and there’s something itching about the “volume decals”.

First, if I understand what is explained, volume decals can work like boolean operations, so is it usable as a single global subtraction boolean for specified types of actors? Like when I have a set of actors such as a bunch of crates, and I want something in the world to make those crates disappear, like a cloaking field. I could normally use a transition shader with opacity, but that won’t close the mesh, so you can look through it, or has much control over the location, especially if you have more than one of these “fields” in one world, since it’s material based. So I would just place a box and every-time a crate enters that box, it is cut off at the edges until it disappears. This effects doesn’t need any edge effects or something, a straight line is fine.

And two, it says in the release notes that it’s very resource heavy and may never be suitable for real-time use, so why would anyone put time into making a feature that is almost certain to never work out (and that, at least I, have never heard of), yet not adding a feature that many have requested such as the fluid surface actor, which existed in prior versions of the engine and is currently partly working due to the efforts of someone else (so I imagine wouldn’t be too difficult for a skilled programmer, which I am not), and not really a game-specific feature (since it’s related to water, which pretty much everyone wants). There is no hate here :p, I like the feature of volume decals as read above, and I like what Epic is doing with the engine. This is just something that’s in the back of my head, and I’m just wondering what the answer would be. I’m not demanding anything here, and if people think that I’m pushing too hard, then please ignore this second paragraph of me rambling :o. You can’t really write how you want to say something, so some might read this in a different way.

  1. You can do subtraction, but only if the box (or crate) itself is also a volume decal, and in the same decal material. There is no way for the volume decals to subtract from the world or from different decals. Basically you do all the distance fields that need to interact inside one material.

  2. This was an “epic friday” project by one engineer. Epic friday is a time once a month or so that people are allowed to work on whatever they want. It is rare that an epic friday results in a usable checked in feature, but this time it did. Things like this can be useful in many situations and people are using UE4 for many non-realtime uses as well. But it could have its place in a realtime scene if you budget and test accordingly. It is really there for experimentation. There may be some cool uses by combining it with “distance to nearest surface” where you can make realtime waterfalls or something crazy with simple tweaks to the input.

Ah okay. That clears it up. Thanks for your answer Ryan. I’ll experiment with it a bit and see what I can make of it.