Xnormal Bake - Hole in Normal Map

Haftoof

I've been trying to bake up the normal maps for this particular piece...  

The highpoly doesn't have a hole in the spot.  


The Low poly ends up with this minor distortion. 


I have the low poly as closely matched to the high poly and a cage built around it, but this one minor blemish is driving me up a wall.   I've tried re-doing the low and cage, shifting the verts around, couple of different options in xnormal.  Lastly when I attempt to do it with object space it's not there, but tangent space pops up, even when I use xnormals object to tangent converter.  

Any ideas? 

Eric Chadwick

Is it along a UV seam? Can you show the lowpoly in shaded wireframe?

Haftoof

Here's low poly with wireframe... 

And the baked normal map:

Eric Chadwick

Ah. The vertex normals are twisting to such an extreme that you've entered a black hole!

You need to split the vertex normals along the edges of the blade, by adding hard edges there. Also called smoothing groups.

You're making me hard. Making sense of hard edges, uvs, normal maps and vertex counts

Haftoof

Interesting...   I've looked through that thread before, why does it only happen on one side?  

Eric Chadwick

Look at the vertex normals. I'll bet the tip's normal points away from that side. You need to split the tip normal into a few vertex normals, to prevent the gradients from being so extreme.

Haftoof

Here's the vertex normals shown in maya...  I did make all the edges "Hard" which is very minor normal wise, just surprised that it caused an issue.  Can you manually set the vertex normal to resolve the issue? 

Eric Chadwick

Doesn't look like the normals have been split. Try setting the blade edges to be hard. But you dont want ALL edges to be hard, just the ones that are 90 degrees or more.

Macebo

With the low poly, try deleting the face (polygon) you are having problems with, bridge it and remap it. 

Haftoof

Making one of the edges along the piece hard resolves the issue for the most part, deleting the face and remapping didn't do much sadly.  I'll play around with it a touch and see what works best.  Thanks for the help, just weird that it only happens with this particular side...  hmmm

Ah Solved!  I played around with some of maya's set normals, I think you may have been right about the vertex normal on the top vertex.  I used Maya's set vertex normal and it resolved the issue.  Thanks for all the help guys!

Eric Chadwick

It's obvious to me why this occurs.

Once you come to grips with the way normal maps work in cooperation with the vertex normals, you'll see why your extreme gradient created the hole.

In the link I posted, watch the video, and most importantly, replicate the workflow he explains... to see for yourself exactly how it works. Just watching the video is not enough.

Macebo

I remember having a similar issue... but i resolved in a "extreme" way: remodeling the entire problematic part lol

Thanks for the info, Eric. I didn't know what caused it.

Haftoof

Ah I see...   The tightness of the triangles at the top are dorking up the normal mapping and because the gradient was to extreme on that one point (the top triangle) you end up with an artifact, creating a hard edge cleans up the issue.