
There basically are two issues here: in smooth mode (and all non-tangent normal map types) it doesn't invert the normal for backfacing polys; on the other hand for flat shaded tangent type it is inverted too soon. This fix does a brute force correction by checking the backfacing flag. Reviewers: #cycles, brecht Reviewed By: #cycles, brecht Differential Revision: https://developer.blender.org/D2181