Check winding order of input triangles

[kylebarron]

It looks like (py)martini creates a mesh with vertices (at least sometimes) in clockwise order, while the Quantized Mesh spec requires counter-clockwise winding order.

e.g. here are the first three 2D vertices, and it looks like they define a clockwise triangle

So I should add an option, probably True by default, that checks the input geometries and flips the order of indices if the triangle is in clockwise winding order.

It looks like it shouldn't actually be too slow to check, though it might be best in Cython... not sure if I can vectorize it easily

• Stackoverflow answer, a fast method for checking winding order
• explanatory blog post
• wikipedia

This might solve #9 , #11

[kylebarron]

You should be able to do this vectorised. Use positions as a lookup table, then you should be able to apply indices, to get triples of coordinates. Then just do the simple algorithm above and flip the order of indices where necessary