Bizarre topology

[Spinell]

I really do love hunting for some free models online: I found it the most intuitive way to learn modeling, reshaping and just cutting and arranjing meshes. It's a hole lot of fun (kinda like lego!)

BVut I have come across a really bizarre thing. Again, free models so I'm never expecting something spectacularly well-made, but... well, take a look at this:

 

I've never seen anything like this before. I'm posting it here simply because I'm curious as to why this mesh looks like this and why this happens (so I can avoid it myself). I've been playing around with it all afternoon (had nothing better to do) and for the life of me I can't understand what's happening here. I tried removing doubles, but nothing happened. It has no vertex groups, no modifiers, no materials, nothing I could find that was causing this. It didn't even have overlapped faces.

Anyone have any guesses what's happening here? Now I'm really curious.

[Rahkis Andel]

Well, it certainly looks like it has bizarre topology, but I doubt that has anything to do with it.

It looks like it's probably a variety of issues. First of all, assuming this is a blender screenshot, select all verts and press (ctrl + n). That will recalculate all normals. Then open the UV window and take a look at the UV layout. If you could screenshot that, that would probably show the problem.

Edit: After reading it again, I'm thinking it's just flipped normals. If you have no material applied, the UVs shouldn't matter.

[arton Rotaru]

If you are reffering to the shading artefacts, that's most likely due to messed up vertex normals. (Not to confuse with surface normals.)

[Codewarrior Congrejo]

As the others already said, it's most likely the normals, the dark spots are a good pointer for that.

But to mention that - it doesn't need to be 'messed up'. Depending on the engine or rendertypes it was created for, it is not an uncommon tactic to actively set varying normal directions to achieve a certain optical behaviour. (especially on hair - so it doesn't appear to flat and has changes in its visual appereance)

 

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[Rahkis Andel]

That's interesting. I've never heard of varying normal direction on purpose. Learn something new everyday.

[arton Rotaru]

If you are using Blender, you are out of luck with manipulating vertex normal directions manually anyway. That's one of the weak spots of Blender.

[Gaia Clary]

There are a few Blender addons available which try to add editing of vertex normals. But they all are somewhat experimental because Blender frequently recalculates the vertex normals and destroys the results of these addons.

Blender development is currently checking how full support for vertex normal editing could be implemented in Blender. That would include support of generative modifiers as well (modifiers which create vertices). But that is tricky so we won't see it "next week" 

However for Avastar users there IS a small addition already available, which allows to weld the vertex normals of adjacent objects if the adjacent vertices match. The feature works reliably because we have added it into the Avastar Collada exporter, thus it does not suffer from blender's own ideas how vertex normals should look alike :matte-motes-sunglasses-3:

Here is a quick demo image  from a multi part character (3 parts...) with welded vertex normals:

[arton Rotaru]

That's cool actually! And certainly better than nothing at all. The lack of editing vertex normals in Blender was one of the reasons why I moved away from it. Because I edit vertex normals on almost any mesh I upload to second life.

[Rahkis Andel]

I've been having a ton of trouble with shading between different parts with shared vertex locations.

If that result is only possible with Avastar right now, I guess I'm sold.