Does it Pack

packs.rs

#[derive(Copy, Clone, Debug)]
struct Tile {
    /// A - B - C
    /// |       |
    /// H       D
    /// |       |
    /// G - F - E
    /// 
    /// A = 0
    /// H = 7
    /// 
    /// CounterClockwise winding
    /// 
    /// Packs into 8 bits?
    /// 7             0
    /// c c s s s e e e
    /// 
    /// c: edge curve
    ///     0 = linear
    ///     1 = concave
    ///     2 = convex
    ///     
    /// s: start point
    /// e: end point
    /// 
    /// EMPTY:
    ///     start = 0
    ///     end = 0
    ///     curve = 0
    ///     
    /// FULL:
    ///     sentinel?
    ///     c = 3?
    ///     
    ///     or
    ///     
    ///     start = 7
    ///     end = 7
    ///     
    ///     both!
    ///     
    ///     full = 0xff
    ///     
    packed: u8
}

impl Tile {
    fn empty() -> Tile {
        Self {
            packed: 0
        }
    }

    fn full() -> Tile {
        Self {
            packed: 0xff
        }
    }

    fn invert(&self) -> Tile {
        let t = self.packed;
        Self {
            packed: t & 0xc | (((t >> 3) & 0x7) | ((t << 3) & 0x38))
        }
    }

    fn rot(&self, d: i32) -> Tile {
        let t = self.packed;
        let start = (((t & 0x38) >> 3) as i32 + d * 2) % 8;
        let end = ((t & 0x7) as i32 + d * 2) % 8;
        Self {
            packed: t & 0xc | (start << 3) as u8 | end as u8
        }
    }
}