pointAt method
Get the point at x/y factor (where 0, 0
is center, -1, 0
is left
center, 1, 0
is right center).
Implementation
Vec2D pointAt(double xf, double yf) => Vec2D.fromValues(
left + width * (xf + 1) / 2, top + height * (yf + 1) / 2);