Ink outline for mobile ?

Would it be faster (performance wise) to create ink outline (inverted) hull of a model in 3D app and bring it into UE4, or make material where mesh gets expanded along normals, inverted and colored black ?

If there is no difference, how do I approach material way ? Do I need to have actual copy of the model in the scene with inverted/expanded material, or can ink outline be done in the same material on the actual model (without having copy of the mesh in the scene) ?


As far as I can tell you cannot actually invert a mesh through a material in Unreal. You can invert the normals, but the surface direction is defined by the winding order of the vertices of the model so the surface will always face the direction it does when imported.

So if you are going to use geometry, you have to duplicate the surface and flip it before importing.

Got it. So basically old-school way of doing ink outlines with geometry.

Yep, one thing though if you haven’t done much of this in the past, the inverted geometry method only works really well on models that are mostly convex with unified normals. If your model has concave surfaces or sharp creases you will get areas where the surface clips the outline geometry and appears to cut or offset the outline. It’s hard to describe, but you will know what I mean when you see it. It’s easy enough to account for when modeling, but it’s something to be aware of.

I don’t know much of anything about mobile performance considerations but I do know you can get a decent result with a post process and as few as 5-9 pixel samples depending on how accurate you want the edge detection to be. It would be somewhere around 100 instructions. Is that something that mobile could handle?

I was going got this kind of ink outline:

(default blueprint style)

however, the author of this material pack said it’s not possible to achieve this on mobile. So I am not sure post process is a way to go for clean and tight inks on mobile.

No post process materials work on the mobile rendering pipeline. I think your only solution may be the inverted shell or some sort of intense fresnel material