[Niagara 4.25] Particle Decals Mini Tutorial

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#1

Particle Decals Mini Tutorial

The intention of these mini tutorials is to have easily searchable reference for implementations of some of the newer (or altered) features in Niagara.

While waiting for Epic to (pretty please) implement decal renderers, I thought I’d share a little trick to creating pretty convincing decals inside of Niagara. (kinda)

The goal is to use WorldPositionBehindTranslucency, which @imbueFX shared a few months ago, to recreate the behaviour of decals for translucent and additive materials.

The result will look something like this:

Step 1.
Here’s the material we are going to be using

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  • Essentially, We calculate the mesh particle localspace position, but unstead of using the position of the fragment we are drawing, we using WorldPositionBehindTranslucency to find the surface position behind it.

  • After that we scale and offset and saturate the uv’s to create one distinct tile of the texture. (you could also set tiling in the texture settings, instead of saturating)

  • We also calculate a zMask, allowing us to fade the decal in and out when it moves outside of the z-range of our decal.

Step 2.

  • In the material settings, set Blend Mode to Translucent or Additive, and make sure the material doesn’t cull back faces.
    image
  • In the advanced Translucency settings, make sure to disable depth testing as well, otherwise we won’t be able to see our decal up close.
    image
  • Under Usage, Enable Used with Niagara Mesh Particles
    image

Step 3.

  • Create a new empty emitter and a mesh renderer.
  • I also added an Update Mesh Orientation module to make my decal rotate over time
    image

Step 4.

  • In the Mesh Renderer Module, for Particle Mesh, use a cube with it’s pivot in the center.
  • Also override the material of that cube to be our newly created material.
    image
  • Make sure Local Space is on in the Emitter Properties Module.
    image
  • In the Initalize Particle Module, we can use Mesh scale to scale our decal.
    image

Please let me know if you don’t understand something, or if I made a mistake somewhere.

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#2

I have been posting these tutorials in different threads, because I believe they don’t concern similar enough topics. Furthermore asking and answering of questions is a lot less confusing if you can just ask on the correct thread instead of having to reply to a specifc post in that thread.

However if people rather I wrap all of these neatly into one thread I can do so as well.

Please let me know which one you prefer.

  • Seperate threads per topic.
  • One mega thread with all the tutorials as seperate posts

0 voters

4 Likes
#3

Thank you so much for sharing this knowledge ! I’m quite new on Unreal, I’m sure this will help me for few effect !

1 Like
#4

That is WICKED :smiley:

1 Like
#5

deferred decal was too heavy, so, for translucent, additive material. awesome!

1 Like
#6

https://www.youtube.com/watch?v=jyzg3tNjcis

Works like a charm! Thanks Niels :sparkles:

2 Likes
#7

I discovered a small issue in the material.

We need a saturate node here before the sine to avoid repetition in the z-mask
image

I changed the original post, but if you followed the tutorial before I recomend fixing this.Otherwise you will notice weird problems near steep edges etc.

#8

in this way to create decals how to set something like character do not affected by decal ？

1 Like
#9

The material in its current form cannot exclude actors. You could probably extend it to allow for exclusion using depth stencils, but in cases where a specific actor should not be projected on, standard decals should probably be used.

How to create a water trail for a ship on moving water?
#10

For anyone wondering how to resolve the decal smear (to a degree) I asked my coworker for an assist and wanted to share the knowledge.

I was getting the left hand result with the above and wanted the right hand.

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This addition to the bottom portion of the material will get you the right hand version

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Add this to the bottom portion of the material and multiply it by everything previously going into opacity. So your new material should look like this:

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image1421×680 166 KB

Hope it helps someone :smiley:

10 Likes
#11

Hi, just wanted to acknowledge the reply here.

This will probably not work for people using the forward renderer (mobile, vr, etc), you can use the z mask of the shape to adjust fadeout and limit decal stretching in that case.

This method also doesn’t work if you rotate the decal over another axis than the z-axis. You can transform the world normals to local space to solve that!

Thank you Shannon for this valuable addition! :fire:

1 Like
#12

Oh good to know, thanks for the info. I’m finding it really hard to tell what will and won’t work for VR/mobile actually. Is there a guild/rule of thumb/ anything that’s helpful in discerning what will and wont work? Also, is there another implementation that WOULD work for mobile that doesn’t have the smearing?

#13

It IS really hard to know what works and won’t :smiley:
Both VR systems and Mobile don’t have that much runtime memory to work with, so deffered rendering would be a huge hit on that (if it works at all). That rule might not hold very long though with the speed at which they change…

If you don’t have the g-buffer available your best bet I think, is to limit the thickness of your decal.
You could also try tri-plannar projection based on the differentials, but that will probably give you hard edges.