What is a Blender Weighted Normal ?

Weighted Normals are viewed by many hard-surface modellers as a sort of magic wand. They use the Weighted Normal modifier without having much clue what it actually does and why. Sometimes it helps fix shading errors and sometimes it doesn’t . With all due respect to those wonderful programmers and documenters in the blender.org headquarters, Blender’s documentation for this modifier is a bit complex for the average user to grasp.

The problem that the Weighted Normal modifier addresses is the strange shading which appears on flat surfaces with bevels connected to them:

Strange shading
Strange shading

Let’s check out the wireframe and see if the geometry is OK:

Wireframe view
The Wireframe view

Looking at the wireframe view it looks all right. There are no extra doubled vertices to be merged. There are 4 large Ngons, but they are absolutely flat, so they shouldn’t cause any trouble. The mesh appears to be clean. So it’s head-scratching time…

So we try the Weighted Normal modifier and see whether it has any effect. Add the Weighted Normal modifier to the bottom of the modifier stack :

Weighted Normal Modifier at Bottom of Stack
Weighted Normal modifier added
Weighted Normal Modifier added
Shading good. Problem solved!

The following explanation is undoubtedly not very comprehensive, but perhaps it will give a beginner a starting point in understanding this modifier.

Every flat surface has a normal that points outwards at 90 degrees to the face. Every bevel has its own normal for each face segment. When smoothing is applied, Blender tries to average out the adjacent normals to provide the illusion of a smooth curve. The problem with this is that a large flat face next to a small thin bevel will be influenced excessively by the bevel’s normal. The idea of the weighted normal is to give the large face a more powerful influence in the decision by the blender engine to display the smoothing of the curve. If the normal of a large flat surface is given more weight, it will be rendered more realistically because it has more influence. So the weighted normal modifier gives extra influence to the normals of a larger area face.

Here is a link to an excellent video produced by Gleb Alexandrov of Creative Shrimp if you’d like to learn more about this magic modifier.

It’s easy to use this modifier in practice – just add it to the modifier stack and see its effect without changing any other parameter. In most cases, you don’t have to do anything to the default values to get the benefit of a smoother-looking surface without shading nasties. Sometimes, however, it is necessary to increase the weight. If it has no effect, just disable it in the viewport and get your hands dirty fixing your mesh.

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