How do I fix this weird lighting problem?

Question

I'm making a small game in Unity, and some models are displaying very ugly shading. The shading usually looks funky along the edges between triangles. I'm pretty new to working in 3D; I bet this is an artifact of vertex lighting, but I'm not sure, and I'm not sure how to fix it.

Here you can see the worst example of this problem:

Low-quality lightmapping is visible in that shot, but I'm asking about the visible bands and weird shapes visible on the surface of the orange mesh in the foreground. The mesh was built and UV-mapped in Blender, and is using a standard bumped diffuse shader. There is a light behind and above the camera; all other lights in the scene are pretty far away. What am I doing wrong, and how can I do better?

EDIT: Below is the wireframe for this model in Blender.

Answer 1

It looks like your vertex normals might be messed up. Each vertex's normals should be perpendicular to its face (parallel with the face normals that your wireframe image shows), and you'll need separate vertices for the corners, one for each face that meets at a corner.

Answer 2

That looks like a vertex normal issue. Not having used Blender I'm not sure what options you have to see/modify the normals directly at the vertex level.

The first thing I would do to test, is break off the front surface from the rest of the object and see if it lights correctly. If that works then you could just export it as 2 parts, front & back faces as one object and then side parts as another.

Answer 3

I know this is an old thread, but I stumbled over it, so maybe someone else can benefit from this answer: The problem is: you are trying to interpolate (smooth shading) normals over a 90° angle which most of the time leads to problems.

There are multiple solutions for this: 1. set the shading to flat (T-Menu) 2. Select all edges with an angle > 50 (or higher, toy around a bit), press CTRL E -> mark sharp. Unity can read that information. It will split the vert. normals at the marked edges instead of trying to interpolate them. 3. Use an edge split modifier to actually split the mesh at the angle you specify (I would recomend the upper one in this case) 4. Use a bevel modifier with a depth of 2 or higher. I would recommend this option, it makes the mesh a bit more high poly, but also more realistic. Be sure to either mark the edges you want beveled yourself or choose angle as the limitation mode.

Answer 4

If you're actually using lightmapping, Unity has a modle import setting to Generate Lightmap UVs which would probably solve your problem.