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.
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.
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.