Figure Asymptote ccw -- 001
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Usage of the algorithm "Simple Polygon Orientation".
Show ccw/fig0010.asy on Github.
Generated with Asymptote 3.00-0.
Categories : Surveys | Path Orientation
size(8cm, false); real signedArea(pair [] pt) { // Return the signed area of a simple (NON CROSSED) polygon of vertex "pt" // Retourne l'aire algébrique d'un polygone NON CROISÉ pair [] pt_= copy(pt); real n=pt.length, sa=0; pt_.push(pt_[0]); pt_.push(pt_[1]); for (int i=1; i<=n; ++i) sa +=pt_[i].x * (pt_[i+1].y - pt_[i-1].y); return sa/2; } bool counterclockwise(pair [] pt) { // Return "true" if the polygon (SIMPLE CURVE i.e. NON CROSSED) // of vertex "pt" is counterclockwise // Retourne "true" si le polygone (NON CROISÉ) de sommets "pt" // est dans le sens des aiguilles d'une montre return (signedArea(pt) > 0); } pair [] reverse(pair [] pt) { pair [] pt_=copy(pt); int begin=0, end=pt.length-1; while (begin<end) { pair temp=pt_[begin]; pt_[begin]=pt_[end]; pt_[end]=temp; ++begin; --end; } return pt_; } pair [] counterclockdirected(pair [] pt) { if (counterclockwise(pt)) return pt; else return reverse(pt); } path polygon(pair [] pt) { int l=pt.length; guide opath; for (int i=0; i<l; ++i) { opath = opath--pt[i]; } return opath; } pair [] pg = {(0,0), (1,0), (1,1), (2,2), (-1,1)}; draw(polygon(pg)--cycle, Arrow(Relative(.1)), BeginBar); draw(polygon(counterclockdirected(reverse(pg)))--cycle, Arrow(position=Relative(.2), FillDraw(red)), BeginBar);