public void div(double r, XYPoint origin)
{
reduce(origin);
div(r);
add(origin);
}
public void mul(double r, XYPoint origin)
{
reduce(origin);
mul(r);
add(origin);
}
public void add(XYPoint p)
{
x += p.x;
y += p.y;
}
public void reduce(XYPoint p)
{
x -= p.x;
y -= p.y;
}
public XYPoint(XYPoint p)
: this(p.x, p.y)
{
}