It’s been over 2 years since I posted about a method to recalculate normals in Unity that fixes on some of the issues of Unity’s default RecalculateNormals() method. I’ve used this algorithm (and similar variations) myself in non-Unity projects and I’ve since made minor adjustments, but I never bothered to update the Unity version of the code. Someone recently reported to me that it fails when working with meshes with multiple materials, so I decided to go ahead and update it.
You might have noticed that, for some meshes, calling Unity’s built-in function to RecalculateNormals(), things look different (i.e. worse) than when calculating them from the import settings. A similar problem appears when recalculating normals after combining meshes, with obvious seams between them. For this post I’m going to show you how RecalculateNormals() in Unity works and how and why it is very different from Normal calculation on importing a model. Moreover, I will offer you a fast solution that fixes this problem.
This article is also very useful to those who want to generate 3D meshes dynamically during gameplay and not just those who encountered this problem.