s0rg/grid

package grid

import "image"

type dir uint8

const (
    North dir = iota
    East
    South
    West
    NorthWest
    NorthEast
    SouthEast
    SouthWest
    Up        = North
    Right     = East
    Down      = South
    Left      = West
    UpLeft    = NorthWest
    UpRight   = NorthEast
    DownRight = SouthEast
    DownLeft  = SouthWest
)

var coords = []image.Point{
    {X: 0, Y: -1},  // N
    {X: 1, Y: 0},   // E
    {X: 0, Y: 1},   // S
    {X: -1, Y: 0},  // W
    {X: -1, Y: -1}, // NW
    {X: 1, Y: -1},  // NE
    {X: 1, Y: 1},   // SE
    {X: -1, Y: 1},  // SW
}

var (
    DirectionsCardinal = []dir{
        North,
        East,
        South,
        West,
    }

    DirectionsDiagonal = []dir{
        NorthWest,
        NorthEast,
        SouthEast,
        SouthWest,
    }

    DirectionsALL = []dir{
        NorthWest,
        North,
        NorthEast,
        East,
        SouthEast,
        South,
        SouthWest,
        West,
    }
)

// Points returns displacements for given directions, in requested order.
func Points(dirs ...dir) (rv []image.Point) {
    rv = make([]image.Point, len(dirs))

    for i, d := range dirs {
        rv[i] = coords[d]
    }

    return rv
}

// Invert returns opposite direction.
func (d dir) Invert() (rv dir) {
    switch d {
    case North:
        return South
    case East:
        return West
    case West:
        return East
    case NorthEast:
        return SouthWest
    case SouthWest:
        return NorthEast
    case NorthWest:
        return SouthEast
    case SouthEast:
        return NorthWest
    case South:
    }

    return North
}