public WpfArc(Point2 p1, Point2 p2, Point2 p3, Point2 p4)
{
var rect = Rect2.FromPoints(p1, p2);
var center = new Point2(rect.X + rect.Width / 2.0, rect.Y + rect.Height / 2.0);
double offsetX = center.X - rect.X;
double offsetY = center.Y - rect.Y;
double minLenght = (double)Math.Max(offsetX, offsetY);
double length1 = center.DistanceTo(p3);
double p3x = p3.X + (p3.X - center.X) / length1 * minLenght;
double p3y = p3.Y + (p3.Y - center.Y) / length1 * minLenght;
double length2 = center.DistanceTo(p4);
double p4x = p4.X + (p4.X - center.X) / length2 * minLenght;
double p4y = p4.Y + (p4.Y - center.Y) / length2 * minLenght;
IList <Point2> p3i;
IList <Point2> p4i;
Line2.LineIntersectsWithEllipse(center, new Point2(p3x, p3y), rect, true, out p3i);
Line2.LineIntersectsWithEllipse(center, new Point2(p4x, p4y), rect, true, out p4i);
Point2 start;
Point2 end;
if (p3i != null && p3i.Count == 1)
{
start = p3i.FirstOrDefault();
}
else
{
start = new Point2(p3x, p3y);
}
if (p4i != null && p4i.Count == 1)
{
end = p4i.FirstOrDefault();
}
else
{
end = new Point2(p4x, p4y);
}
double angle = Line2.AngleBetween(center, start, center, end);
bool isLargeArc = angle > 180.0;
double helperLenght = 60.0;
double lengthStart = center.DistanceTo(start);
double p3hx = start.X + (start.X - center.X) / lengthStart * helperLenght;
double p3hy = start.Y + (start.Y - center.Y) / lengthStart * helperLenght;
double lengthEnd = center.DistanceTo(end);
double p4hx = end.X + (end.X - center.X) / lengthEnd * helperLenght;
double p4hy = end.Y + (end.Y - center.Y) / lengthEnd * helperLenght;
P1 = p1;
P2 = p2;
P3 = new Point2(p3hx, p3hy);
P4 = new Point2(p4hx, p4hy);
Rect = rect;
Center = center;
Start = start;
End = end;
Radius = new Size2(offsetX, offsetY);
IsLargeArc = isLargeArc;
Angle = angle;
}
