sequence.go

package main

import (
	"github.com/go-gl/mathgl/mgl32"
)

func squareSpiral(n int) []mgl32.Vec3 {
	out := make([]mgl32.Vec3, n)
	up := mgl32.Vec3{0, 1, 0}
	left := mgl32.Vec3{-1, 0, 0}
	down := mgl32.Vec3{0, -1, 0}
	right := mgl32.Vec3{1, 0, 0}
	orbit := 0
	i := 0
	position := mgl32.Vec3{0, 0, 0}
	base := -1
	for i < n {
		out[i] = position
		i++
		// compute the next position
		switch {
		case i == (2*orbit+1)*(2*orbit+1):
			// go to the next orbit
			orbit++
			base = i - 1                  // last index in the previous orbit
			position = position.Add(left) // the first in the left arm
		case i-base <= 2*orbit:
			// still in the left arm
			position = position.Add(up)
		case i-base <= 4*orbit:
			// still in the upper arm
			position = position.Add(right)
		case i-base <= 6*orbit:
			// still in the right arm
			position = position.Add(down)
		case i-base <= 8*orbit:
			// still in the lower arm
			position = position.Add(left)
		}
	}

	return out
}