Geometry requirements

No N-gons

Mesh should be made up of quads and triangles, there should not be any n-gons. Best practice is to use as little triangles as possible and keep quads without triangulation where possible. Keep in mind that the geometry will still be triangulated automatically if it is imported into most game engines or converted into certain formats, so in some cases it might be better to pre-triangulate certain faces to make sure they do not get triangulated the wrong way and create shape or shading issues, like with non-convex faces.

How to solve

• Some vertexes of the N-gon could be connected with edge, so the end result will be quads and triangles instead of one N-gon.
• All or several vertexes of the N-gon could be welded together.
• Automatically:
  • turn all N-gons to quads in 3ds Max by using Turn to Poly modifier
    
  • turn all selected N-gons to triangles in blender by triangulating selected N-gon faces (Ctrl + T shortcut). How to find and select N-gons is described in the Locate N-gons infographics which is presented above.
    

No non-manifold geometry

Non-manifold geometry generally refers to geometry that could not realistically exist and could not be unfolded into a 2d shape; this mostly appears when a single edge is shared by more than two faces. This should be always avoided as this can create all kinds of technical issues and the model might not be usable at all in some software.

How to solve

1. Detect non-manifold vertices/edges.
   1. Select a geometry object.
   2. Enter Edit Mode by pressing Tab key.
   3. Use Vertex or Edge select mode.
   4. Make sure that all vertices/edges are deselected.
   5. Go to Select → Select All by Trait → Non Manifold
      
   6. Deselect Boundaries from the Select Non-Manifold menu. (Geometry with open edges is acceptable)
      
2. When non-manifold vertices/edges are detected issue can be fixed by:
   • Deleting/separating faces which which have non-manifold vertices/edges.
   • Deleting loose geometry (vertices/edges).
   • Flipping normals of the adjacent faces which has normals pointing in opposite directions.
   • Merging non-manifold vertices.

No backfaces

Visible backfaces should be avoided, if both sides of a face are going to be visible, then inside geometry or thickness should be added to that area. Even though backface visibility can be enabled in game engines and software, it should not be relied upon as backfaces can create technical problems or limitations.

Smoothed geometry

Geometry should have some kind of smoothing applied, it should not be fully faceted. At least one smoothing group should be applied to the mesh with as few smoothing groups as possible used.

How to solve