How to do rim erosion that is screen aligned instead of view aligned

[peak crater]

Thank you to anyone who responds.

Originally I was following this https://cyn-prod.com/stylized-paint-shader-breakdown to attempt to create rim erosion. So far I have it as view aligned but it's not achieving the same effect that I wanted, which is the rim offset no matter what angle you're viewing from, as shown with the cube image. Inside the blue outlines should be the rim offset.

Another person also told me that there's going to be issues with using vertices to calculate these types of things (specifically with complex geometry) so I was wondering if there's a different way. From my understanding, you'd still want the calculation for the fresnel, but I'm not sure if you should be using something to replace Camera Vector and/or VertexNormalWS to find the dot product.

I am also very sure that using vertex colors actually don't lower the calculation cost compared to just using the vertex normal world space. You'd have to convert the vertex colors to the vertex normal world space anyways. Probably making a normal map would give you more control then.
https://youtu.be/s8N00rjil_4?si=lRUHRI9JQ75s9skm&t=330

[peak crater]

Hopefully this shows the problem and what I'm trying to fix. I really just want the rim erosion to occur at the corners of the mesh. If there's a way to modify the fresnel so it does that, I'd appreciate it. I'm assuming I have to fix the calculation for the fresnel somehow.

[peak crater]

For the rim offset, the goal is to have solid model in the center, with a solid shader and an outer shell thats got the panning corroded material all over it. The problem is finding where the mesh ends. I've achieved this so far by using an inner fresnel and outer fresnel but I think I need to do this in post processing via stencils in order for it to actually look right.

1. Inside the base material, plug in for the opacity mask.
2. MF_ShellCalculation
3. MF_ColorRamp

Outline is a different overlay material and also needs to be fixed as well. Probably use post-processing by this point.

Or I can attempt to do this for rim erosion. Outline will still have to be post processed I think, using Sobel or Laplacian.

You can shift the inner object vertex in a material to inflate/deflate and create the same effect - at a higher cost ofc.

You can do this on a single object, and with a single material using different UVs for the inside and outside shells…

[peak crater]

https://forums.unrealengine.com/t/how-to-create-customisable-rim-erosion-and-offset-outline-for-mesh/1369825/2

Will update in here. So far I made two instances, one for the 'inner shell', one for the 'outer shell'.

[robust sapphire]

I think there is a view node that gives you a vector from camera to pixel rather than camera forward. Alternatively just delta the world position with the camera position. Either works

[peak crater]

I'll try doing that when I get on the computer, been a busy week and I'm actually on my phone right now. Thank you, Mal. Another person also talked about another method to get inner/outer shell with two different UVs and I've gotta test that soon.

[peak crater]

When you are talking about the view node that gives you a vector from camera to pixel, are we talking about CameraVector?

[robust sapphire]

Yes

Sorry, mixed it up with CameraDirectionVector

[peak crater]

No problem, I'm just curious, would that work with post processing? I've seen it used for overlay material outlines (which was what I used originally) and then using fresnel to determine where the outline shows up but that doesn't work with flat faces so that's the reason why I was trying to use post processing.

[robust sapphire]

Yeah I use it in post process for many things

But I would be careful to do it that way, it's a bit of a naive approach for outlining

Using laplace convolutions makes much more sense

[peak crater]

Laplacian or Sobel?

[robust sapphire]

You basically check if there's a difference in depth or normal between pixels, and if the difference of either is high enough (generally using relatively small values), you make that pixel black

[peak crater]

From my understanding Laplacian is considered better, uses one kernel and second derivatives? But therefore is more sensitive to noise?

[robust sapphire]

Both do essentially the exact same thing, laplacian just does it in one sweep

Well, it's the same thing in our context

Not in a broader sense

[peak crater]

Mhm. I remember following the toon outline tutorial and I'm pretty sure the person ended up using pixels.

Creating a kernel, then checking for difference in depth/normals.

[robust sapphire]

You'll only need to check one pixel in each direction, any more is needlessly expensive

If you want thicker outlines, check pixels further out

[peak crater]

That makes sense.

https://youtu.be/9KvUfnrHcqM?si=qKQvRiPNDYZN0ysA

Yea I remembered following this essentially.

(I know this is slightly off topic, but I posted #𝓖𝓔𝓣-𝓗𝓔𝓛𝓟 message, I don't know if you've used TGraphTask but do you know why it's giving me a nullptr when I'm trying to access the TSet? And it's fine if you don't.)

And again, I really do appreciate your help so far.

[peak crater]

I'm curious, how would you offset the outline then this way? If it's possible. Like would you take the pixel you've determined that is an edge then multiply the location of it 'outward'? If that makes sense. I'm just trying to wrap my mind around this.

[robust sapphire]

You wouldn't generally

What you can do is use custom depth as some sort of filter for edge thickness

[peak crater]

That makes sense.

I'm curious, in Blender there's a modifier for multiple strokes, in UE, is it possible to recreate that effect via post processing? I don't know if there's a specific algorithm for that. From my understanding, Grease Pencil is actually 3D though right, so it 'wraps' around an object? (Limited knowledge of Blender).

https://youtu.be/G1ZKUZS_DJI?si=QShUcZd9zJZds0QG&t=79

If not then that's understandable. I'm pretty newb at visuals.

[robust sapphire]

Hmm yeah I guess it could be done with edge detection on a duplicate mesh, then inflate that duplicate with wpo along normal

not in post process though

[peak crater]

That makes sense, I think I saw that mentioned in the article, the problem is draw calls, and I think that's why the person used instances.

[robust sapphire]

then add some noice for the offset and mask off a bit of it with additional noice

noise*

[peak crater]

Thanks, Mal. Shaders are pretty fun, hahhaahahah.

[robust sapphire]

I mean, drawcalls aren't great, but if you limit the effect to some things in the scene I wouldn't worry

I wouldn't worry about drawcalls this early in learning

Focus on functionality

[peak crater]

That makes sense.

Right.

I think what I'm wary of is I do have a lower end computer, so I'm afraid of lagging myself. I don't exactly have a budget to spend right now and the economy's in shambles so.

Again, thanks Mal, for the responses and help.

[robust sapphire]

Oh no, I sit on really bad hardware most of the time. It's not gonna be a problem.

Inefficiency is only really a problem when it adds up. Doing something really expensive when it's the only thing in the scene is absolutely nothing to worry about. But when you put everything together it's gonna suck

But for learning, you don't have to worry