public bool isConvexVertex(Point v1)
{
var v0 = prev(v1).vec;
var v2 = next(v1).vec;
return(GeomUtils.cross(v1.x - v0.x, v1.y - v0.y, v2.x - v1.x, v2.y - v1.y) > 0);
}
public bool isConvexVertexi(int i)
{
var len = this.Count;
var v0 = this[(i + len - 1) % len].vec;
var v1 = this[i].vec;
var v2 = this[(i + 1) % len].vec;
return(GeomUtils.cross(v1.x - v0.x, v1.y - v0.y, v2.x - v1.x, v2.y - v1.y) > 0);
}
public Point _centroid()
{
var x = 0.0;
var y = 0.0;
var a = 0.0;
forEdge((Point v0, Point v1) =>
{
var f = GeomUtils.cross(v0.x, v0.y, v1.x, v1.y);
a += f;
x += (v0.x + v1.x) * f;
y += (v0.y + v1.y) * f;
});
var s6 = 1 / (3 * a);
return(new Point((float)(s6 * x), (float)(s6 * y)));
}
public List <Polygon> cut(Point p1, Point p2, float gap = 0)
{
var x1 = p1.x;
var y1 = p1.y;
var dx1 = p2.x - x1;
var dy1 = p2.y - y1;
var len = this.Count;
var edge1 = 0;
var ratio1 = 0.0f;
var edge2 = 0;
var ratio2 = 0.0f;
var count = 0;
for (var i = 0; i < len; i++)
{
var v0 = this[i];
var v1 = this[(i + 1) % len];
var x2 = v0.x;
var y2 = v0.y;
var dx2 = v1.x - x2;
var dy2 = v1.y - y2;
var t = GeomUtils.intersectLines(x1, y1, dx1, dy1, x2, y2, dx2, dy2);
if (t != null && t?.y >= 0 && t?.y <= 1)
{
switch (count)
{
case 0:
edge1 = i;
ratio1 = t.x;
break;
case 1:
edge2 = i;
ratio2 = t.x;
break;
}
count++;
}
}
if (count == 2)
{
var point1 = new Point(p1.vec + ((p2.vec - p1.vec) * (ratio1)));
var point2 = new Point(p1.vec + ((p2.vec - p1.vec) * (ratio2)));
var half1 = new Polygon(this.Skip(edge1 + 1).Take((edge2 + 1) - (edge1 + 1)).ToList());
half1.Insert(0, point1);
half1.Add(point2);
var half2 = new Polygon(this.Skip(edge2 + 1).Concat(this.Take(edge1 + 1)).ToList());
half2.Insert(0, point2);
half2.Add(point1);
if (gap > 0)
{
half1 = half1.peel(point2, gap / 2);
half2 = half2.peel(point1, gap / 2);
}
var v = vectori(edge1);
return(GeomUtils.cross(dx1, dy1, v.x, v.y) > 0 ? new List <Polygon> {
half1, half2
} : new List <Polygon> {
half2, half1
});
}
else
{
return new List <Polygon> {
new Polygon(this)
}
};
}