using System.Collections.Generic;
using UnityEngine;

[RequireComponent(typeof(MeshFilter), typeof(MeshRenderer))]
public class Axis3D : MonoBehaviour
{
    void Start()
    {
        var mesh = new Mesh();
        mesh.name = "Axis3D";
       
        List<Vector3> verts = new List<Vector3>();
        List<Color> colors = new List<Color>();
        List<int> inds = new List<int>();

        // x-axis:
        verts.Add(new Vector3(-1, 0, 0));
        colors.Add(Color.white);
        inds.Add(inds.Count);

        verts.Add(new Vector3(1, 0, 0));
        colors.Add(Color.white);
        inds.Add(inds.Count);

        // y-axis:
        verts.Add(new Vector3(0, -1, 0));
        colors.Add(Color.white);
        inds.Add(inds.Count);

        verts.Add(new Vector3(0, 1, 0));
        colors.Add(Color.white);
        inds.Add(inds.Count);

        // z-axis:
        verts.Add(new Vector3(0, 0, -1));
        colors.Add(Color.white);
        inds.Add(inds.Count);

        verts.Add(new Vector3(0, 0, 1));
        colors.Add(Color.white);
        inds.Add(inds.Count);

        mesh.vertices = verts.ToArray();
        mesh.colors = colors.ToArray();
        mesh.SetIndices(inds.ToArray(), MeshTopology.Lines, 0, true);
        GetComponent<MeshFilter>().sharedMesh = mesh;
    }
}