Ability of flipping normals is still needed if a linear transform with negative determinant is applied. Now the Surface toolbox module is available that can compute the surface normals with an optional flipping, so the functionality is available for the users.

We could compute the correct normals, but currently the model display pipeline does not include normal computation. Normals are computed in some readers and in some modules that generate polydata, but not everywhere (e.g., normals are not computed if the model is imported from an STL file). Probably the best would be to add (optional) normal computation to the model display pipeline. This normal computation could contain automatic flipping. Some cost is associated with the normal computation, the normals have to be stored, and the normals are also affected by the applied transforms, so probably once the normals are computed, the (warped) mesh+normals should be cached in memory. These cached warped models could be used for 3D model display and also for the model/slice intersection display (which is currently broken for non-linear transforms - see 0003615).

So, I think this issue should be resolved along with 0003615, by adding to the display pipeline warping and normal computation step, with caching .

The feature is available in the Surface toolbox module