Short description of error
When Keep Sharp option on the modifier is not set, the modifier smooths normals so long as the Auto Smooth option is set on the mesh. When Keep Sharp is enabled, the modifier would treat all edges as sharp unless you explicitly set faces to smooth shading, regardless of the Auto Smooth angle setting.
Exact steps for others to reproduce the error
- Create a new scene, remove default objects, add a Cone.
- Add a Weighted Normal modifier to the cone, and set mode to Corner Angle.
- Note that the cone is still shaded flat, and modifier reminds to enable Auto Smooth.
- Enable Auto Smooth, leave angle setting at 30.
- The cone would now be smooth-shaded overall.
- On the modifier, enable Keep Sharp.
- The cone would now be flat-shaded overall.
- Right click the cone and Shade Smooth.
- Now the cone appears smooth shaded with a sharp edge at the base.
This behavior is inconsistent, and defeats the purpose of the modifier. If (5) is the correct behavior, and the modifier smooths the normals regardless of face smooth/flat setting, then in (7) one should get a sharp edge between two smooth areas. There's no point in a non-destructive modifier if it relies on manual destructive editing (i.e. explicitly setting face shading). Ideally, one should be able to keep the edit mesh shaded flat and rely on edge sharp setting, Auto Smooth, and Weighted Normal modifier for smoothing shading.