Function is_polygon_simple 

pub fn is_polygon_simple(vertices: &[Vec2]) -> bool

Tests whether the vertices describe a simple polygon. The last vertex must not be equal to the first vertex.

A polygon is simple if it is not self intersecting and not self tangent. As such, no two edges of the polygon may cross each other and each vertex must not lie on another edge.

Any ‘polygon’ with less than three vertices is simple.

The algorithm used is the Shamos-Hoey algorithm, a version of the Bentley-Ottman algorithm adapted to only detect whether any intersections exist. This function will run in O(n * log n)