I don't understand what you mean by 'painting the mesh normals' as that would require modifying the geometry(the mesh) itself. The normals for edges are probably simply the average between the normals of adjacent faces and the normals for vertices are probably just he averaged normals of the edges meeting in that vertex. Usually, I think the normals of a face are just calculated from the triangulation of it and then perhaps averaged for n-gon-faces. The normals are derived from that(normalized cross product of any two vectors that make up the plane of the face). I can create any normals I want, I can use any mesh editing tool I can dream up to create those normals, and I'm guaranteed smooth, mesh-appropriate normals.By my understanding, the mesh is the definition of the geometry itself, the vertices, the edges between vertices and the definition of which vertices or edges form the faces. This is pretty much the nuke level of normal editing. Left to right: base Suzanne, Suzanne with data transferred normals, mesh edited Suzanne used as target of data transfer. Sometimes I'll do a data transfer of normals, by topology, from a copy of the mesh: However, it is relatively easy to recreate most live custom normals in a game engine shader if needed. Note that if the goal is use in a different renderer, you need to apply, and while live custom normals can fix a lot of topo problems, applied custom normals can't.

Again, I can limit with a vertex group I can apply or leave live. This lets me tune normals exactly how I want, but through the use of all of the mesh tools with which I'm familiar I can easily visualize the normals, and with reasonable choices, I'll always get continuous, reasonable normals (unlike manually editing normals):ДЇor this kind of task, nearest face interpolated is my preferred mapping. You can apply the modifier to write the custom normals, or leave the modifier live.ДЇor more complicated normals, I'll generally use a data transfer modifier that copies the normals that I want from some other object. You can tune the mix factor and limit with a vertex group.

These are useful for creating simple spherical or flat normals. Your first tool is a normal edit modifier, which can let you create custom normals from the position of some other object- either radially from the position of that object, or parallel directional normals, from the origin to the object. Thankfully, there are a lot of other great tools you can use to modify normals en masse. It's too easy to screw things up, and you can easily have too many normals to be able to meaningfully tune. While there are a number of ways to individually tune normals, I don't find that useful. I recommend setting autosmooth angle to 180 when messing about with custom normals, as there are circumstances where Blender can create custom normals for only some verts, leading to autosmoothing other verts.

Any tool that adjusts custom normals requires that autosmooth be enabled. There are a number of tools for controlling custom normals.

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