Remaining Freestyle bugs

- Some triangle strips (resulting from the stroke tesselation) are incorrect and show a flip at one or more points

- Crashes. Potentially multiple origins, including, if I remember correctly, a problem with the acceleration grid (some points are found outside the grid although they should be inside). Also, it appears that sometimes a TVertex links to NULL ViewEdges, which shouldn’t happen.

- Visibility problems. Some of these problems are due to the fact that Y-junctions are missing in the current ViewMap (at some point, I refactored the ViewMap and I left the Y-junctions on the side and never got to add them back), for instance that would cause wrong visibility on the silhouette of cylinder’s caps. Some other visibility problems can appear if the mesh is too coarse or has a weird mix of “smooth” and “non-smooth” vertices (vertices that share or don’t share their normals across adjacent faces). In that case, the incompatibility between the model and the smooth silhouettes can make it harder to compute a robust visibility.