🚀 go-pugleaf

In article <1992Jul21.094844.1@camins.camosun.bc.ca> morley@camins.camosun.bc.ca writes:
>Hi!
>
>Ok, this should be an easy one...  Given 3 X,Y points that form a triangle,
>what is the simplest (fastest) way to determine if they are clock-wise or
>counter-clock-wise?  I'm not interested in general polygons of N points,
>just plain old triangles.  Yes, this is for use in a graphics app.
>
>Thanks...
>
>MARK
>morley@camins.camosun.bc.ca
>

Traverse the polygon, calculating 3 cross products (v1->v2 X v2->v3,
v2->v3 X v3->v1), and (v3->v1 X v1->v2), and if the cross products are
positive, the polygon is counterclockwise, otherwise they will be negetive.
Also, if you have a sign flip between the different cross products, then
the polygon is not convex.

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