macro_rules! impl_axis_common { ($A:ident $T:ty) => {
    impl $A<$T> {
        pub fn start_inc (&mut self) -> $T {
            self.start += 1;
            self.start
        }
        pub fn start_dec (&mut self) -> $T {
            self.start = self.start.saturating_sub(1);
            self.start
        }
        pub fn point_inc (&mut self) -> Option<$T> {
            self.point = self.point.map(|p|p + 1);
            self.point
        }
        pub fn point_dec (&mut self) -> Option<$T> {
            self.point = self.point.map(|p|p.saturating_sub(1));
            self.point
        }
    }
} }

pub struct FixedAxis<T> { pub start: T, pub point: Option<T> }
impl_axis_common!(FixedAxis u16);
impl_axis_common!(FixedAxis usize);

pub struct ScaledAxis<T> { pub start: T, pub scale: T, pub point: Option<T> }
impl_axis_common!(ScaledAxis u16);
impl_axis_common!(ScaledAxis usize);
impl<T: Copy> ScaledAxis<T> {
    pub fn scale_mut (&mut self, cb: &impl Fn(T)->T) {
        self.scale = cb(self.scale)
    }
}