void scaling(out double x, out double y)
{
double x1 = 0.0;
double y1 = 0.0;
double x2 = 1.0;
double y2 = 1.0;
Perspective t = new Perspective(this);
t *= Affine.NewRotation(-rotation());
t.Transform(ref x1, ref y1);
t.Transform(ref x2, ref y2);
x = x2 - x1;
y = y2 - y1;
}
Perspective rotate(double a)
{
multiply(Affine.NewRotation(a));
return(this);
}