I'm going to raise this issue up for the 100th time!!

Guys its simple and please if theres someone out there I need to know if this is an engine problem or my problem! actually in any case it becomes my problem.

I want to add a stain or Modulate Unlit decal on the surface of either unlit material or an emmissive standard shader one while using Forward rendering mode (I don’t even know if this works in deffered but I dont care because we are using forward).

**Please allow me to put this in example form: **I am using no lights in the scene and so the materials i have are either unlit or standard shaders with a bit of emmisive on them. Now imagine a ground with one of these materials applied, now also imagine a bomb that explodes on these surfaces!!
How in the world would you go on creating a stained surface without the decals?!

Please don’t tell me to spawn a plane and apply a modulate shader on it becuase thats what i’ve been stuck with and its a real pain believe me!

What’s the problem you’re trying to solve? There’s a decal, but the decal isn’t visible because there’s no lights?

Do you have screenshots, or maybe a github link with a basic example?

Not sure about the limitations of Forward and decals, but you could always do it the way engines without decal systems do… just a floating card and a standard material.

Ah Its a miracle for once some people have replied to a forum post regarding this matter! :slight_smile:

1 - I don’t want to use cards i’ve been doing that already, but they are a problem, first setup time is needlessly troublesome, second spawned cards need to have additional setup such as tracing in order to spawn on uneven surfaces, third they tend to intersect and cutoff with surrounding objects or uneven surfaces like hills or bumps, fourth they don’t work too well with perspective changes because they need to be at a safe offset from the surface so at some point they will simply dissappear.

2 - Deffered and forward suffer from this issues I just tested it on deffered.

3 - You can find an example file below.

Download Link

As you can see the scene has no lights, the plane card with a simple unlit modulate shader works as intended but the decal does not with stain mode or any other mode for that matter.

If this is an issue with how Unreal is dealing with it and there are no solutions then we have to wonder what other methods we can use in order to “project” modulated textures onto uneven and unlit surfaces without resorting to cards.

But first I want to understand what the problem is with decals and with this limitation if someone can put the time to explain it and then we can perhaps discuss about alternatives or solutions.

Does it work if you add a light to the scene? If so, it sounds like a bug to me and you should file a bug report.

[USER=“202133”]William K[/USER] I could not send any insights because life is just crazy, but I have seen all your posts. Indeed, the decal looks not behaving the way it should, but I have made some experiments with your project and I don’t know if you have tried this. It is complicated, but BaseColor seems to not accept texture directly, but it is ok with constants. Check the ending portion and realize that the decal opacity pin behaves like Opacity Mask when you feed a texture to Emissive instead of constant color. You will end up having to make several masks to be able to get decals you want. I placed a dynamic light there because I couldn’t see any color and after it I simply I can’t have a pure black color, but other colors seems ok.

Thank you both for responding and Nilson thanks for taking the time to do the video!

Unfortunately this is still unusable for me since dark multiplied coloration is exactly what i’m after and not colored or brightened projections, you see the primary purpose of these decals in my case are for explosion debris marks (such as the image example below) as well as faking shadows. On top of that the scene must be entirely unlit that means no lights used whatsoever, which is why i need the decal to work (just like a modulate shader is working on the card) in an unlit scene.


Since it seems i’m not the only one with this issue, I hope we can get some feedback from Epic devs to see if there are any solutions to this, if not for now, then for the upcoming versions of UE?

I think posting the project along with detailed description using the bug report is enough. Explicitly ask for the expected result to be the explosion darkened mark as you placed above. There is no reason at least for my understanding it wouldn’t work on forward rendering, so it is important to explain the same behavior happens on deferred (which I also tested), because some time ago I remember someone from Epic commenting on Decals issue for forward rendering, but I failed to find the post on my saved links.

Thanks just submitted this, I hope we get some answers soon.

Any issue number already for us to track it too?

I’m not sure if a ticket is yet created but I did submit and I received an email that they are looking into this and will get back to us once they have something.

When they acknowledge there is an issue, they send an e-mail with the issue number for you to follow up.

I don’t think I received such an email I just checked again. But I did receive an email from a fellow named Jeremy and he mentions they are looking into this, so I am not sure if that acknowledges anything or not yet I guess we have to wait a bit and see.