Sometimes i find myself dealing with meshes, hair cards from video games mostly, which consistent of many many disconnected parts, and Blender can't quite figure out what is supposed to be interior and what is exterior, and recalculating normals results in different strands facing in different directions, causing issues with lighting.
Being that hair meshes can consist of *lots* of strands, going through and flipping them one by one isn't much fun exactly.
One semi-solution i found is to use Normal Edit modifier, with offsetting the origin. That mostly fixes the general direction the strands are supposed to be facing, but also flattens normals a little too much. However, i can then apply the modifier, and just go delete custom normals, which leaves all cards almost facing the right away, except for some small clusters of polygons that end up flipped.
Well, looking for all the flipped polygons is probably even more of a hassle than looking for flipped strands, but i feel like there has to be some kind of tool that could detect and flip those patches. Does anyone have an idea how to do that, or maybe some alternative solution?