Deferred Decal rendering depends on material they are projected on

As suggested in [answerhub][1], I opened a Bug report.

The issue is about Deferred Decals.
I am currently using UE 4.7.6

Issue can reproduced on different ways:

  1. Create an object in the scene (e.g. a Cube)
  2. Assign any material, even an “empty one” (e.g. nothing linked to the Material pins)
  3. Set the visibility of this object to “Actor Hidden in Game” set to true OR “Visible” set to false
  4. Create a Decal and point it to the object
  5. If “Actor Hidden in Game” is set to true, when playing, the decal and the object will not be visible
  6. If “Visible” is set to false, the decal and the object will not be visible both in editor and playing

Going further, Deferred Decal rendering behavior is coupled to the object shader (in particular, to the opacity of the material it is projected on):

  • Change the material of the object to be Transparent instead of Opaque and the decal will not be rendered
  • Change the material of the object to be Masked: the decal opacity will be the same of the one of the object material

I think this could be actually a work as designed, but then:

  • Highlight this limitation in the documentation
  • Provide a primitive to implement decals which do not depend on the material they are projected on

Thanks in advance

Hello lucabelluccini,

Decals function by modifying the shading attributes of the material it is applied, so what you are reporting is as intended. The content examples maps we have, provide some of the different types of decal blending modes to communicate correctly with the various other Material Domains and Blend Modes. Be sure your Material Domain is set to deferred decal, and your Decal Blend Mode is set up to render correctly with the material you are applying it to.

Decal Actor User Guide

Take a look at the documentation and the various sections of Decals to make sure you are using them correctly. You can download the ‘Content Examples’ project to see the images provided in the documentation first hand. Depending on your Material Domain, Decal Blending Mode, the Blend Mode of the material applied, and the Translucent Sorting Priority, your decals will behave differently.


Andrew Hurley

The Material of the Decal itself is a Deferred Decal Material.
I tried all the types of Blend Modes, but once the material of the object the decal is projected on is set to opacity 0 or not visible, the decal will no more work.

It seems we have no option to project a decal on a “invisible”/transparent/not rendered object.

Take a look at these helpful links to show you how to set up your materials and decals to render on transparent objects.

Transparent Material Set Up

Decals with Glass

Let me know if you are still having issues. after going over the links provided.

I will tell you though, if you have an object that is not rendered in your scene, the decal will not function as they depend on the surface they are applied.

Thank you,

Andrew Hurley

Indeed this could be a solution for static decals.
Our project needs decals “a la splatoon” and indeed generating mask to be applied on the object material is not so optimal. Do you have any suggestion?

Unfortunately, this is where my knowledge of Decals becomes limited. The suggestions I provided are the ones I have been able to find, but I am sure if you continue to dig and search, you can find another solution.