Blender School - Topology

 
Today's lesson: Topology.

This is important. Building in Blender can become very frustrating if your model contains bad topology. My models often do, so I'll be taking notes...

1. Topology vs Geometry

• The topology of a mesh is concerned with triangles and polygons, which include quads and Ngons.
• The Geometry of a mesh is concerned with vertices and edges.

2. Shading problems

• You can't make a triangle non-planar, so it will never exhibit shading errors.
  
  
•  If you put a crease in a quad or an Ngon, it will result in shader problems as the shader engine tries to deal with an edge that isn't there. Ngon issues are more obvious as you'll often see multiple triangular elements.
  
  
• In more complex meshes, shading problems happen when there is a break in the flow, which results in the shader producing uneven effects.

3. Common topology problems

•   Non-manifold geometry, such as internal faces that are hidden in the viewport but become apparent if you go into normals view. A telltale sign of this is if edges refuse to be merged because they are supporting a hidden face.
  
  
• Flipped normals occur when an operation on your geometry pushes some elements inside out, so that the normal points inwards instead of outwards. Quick fix: Select all faces, then Shift +N.
  
  
• Disconnected geometry is also hard to spot in the viewport. Easy fix. Select all vertices, then M to merge.
  
  
• Overlapping geometry is very common, usually as a result of a bevel that goes too far. Again, merge vertices if it happens, or ensure that you clamp the bevel to avoid overlaps.
  
  

4. Common shading problems

• Autosmooth isn't enabled. Easy fix: enable it.
• Boolean operations on a curved surface. Add more edge loops!
• Customer Split Normals - If the auto smooth is greyed out, the problem may be caused by Custom Split Normals. You can delete them under the data tab, in the Geometry Data panel. 
• Bent geometry, as mentioned in shading problems.