utils.go

package main

import "math/rand"

type Vector2i struct {
	X, Y int
}

// abs returns the absolute int value
func abs(x int) int {
	switch {
	case x < 0:
		return -x
	case x == 0:
		return 0
	}
	return x
}

// rng returns a random number in a given range
func rng(min, max int) int {
	return rand.Intn(max-min+1) + min
}

// BresenhamLine returns a slice containing all the positions between two positions using Bresenham's Line Algorithm.
// @see http://www.roguebasin.com/index.php/Bresenham%27s_Line_Algorithm#Go
func BresenhamLine(pos1, pos2 Vector2i) (points []Vector2i) {
	x1, y1 := pos1.X, pos1.Y
	x2, y2 := pos2.X, pos2.Y

	isSteep := abs(y2-y1) > abs(x2-x1)
	if isSteep {
		x1, y1 = y1, x1
		x2, y2 = y2, x2
	}

	reversed := false
	if x1 > x2 {
		x1, x2 = x2, x1
		y1, y2 = y2, y1
		reversed = true
	}

	deltaX := x2 - x1
	deltaY := abs(y2 - y1)
	err := deltaX / 2
	y := y1
	var ystep int

	if y1 < y2 {
		ystep = 1
	} else {
		ystep = -1
	}

	for x := x1; x < x2+1; x++ {
		if isSteep {
			points = append(points, Vector2i{y, x})
		} else {
			points = append(points, Vector2i{x, y})
		}
		err -= deltaY
		if err < 0 {
			y += ystep
			err += deltaX
		}
	}

	if reversed {
		// Reverse the slice
		for i, j := 0, len(points)-1; i < j; i, j = i+1, j-1 {
			points[i], points[j] = points[j], points[i]
		}
	}

	return
}