Obstacles

Lesson 9 of 20 in Coddy's Unity Game: Sky Lanes course.

Now the road needs something to dodge. Every piece gets an obstacle in the middle, in a random lane. A method does it, Fill, called for each new piece in Start and again each time a piece goes back to the front.

The first two pieces stay empty, to give the player a moment: the Road counts the pieces it has filled in made.

void Fill(Transform chunk)
{
    made++;
    if (made <= safeChunks) return;

    int lane = Random.Range(-1, 2);
    Place(chunk, barrierPrefab, lane, 0.5f, 0f);
}

Random.Range(-1, 2) is -1, 0 or 1: with whole numbers the second number is never picked.

A recycled piece still carries its old obstacle. Clear destroys every child that has a tag. The floor, dashes and edges are Untagged, so they stay:

void Clear(Transform chunk)
{
    foreach (Transform child in chunk)
    {
        if (!child.CompareTag("Untagged")) Destroy(child.gameObject);
    }
}

Challenge

Easy

In Road add public GameObject barrierPrefab;, public int safeChunks = 2; and private int made;.
Write Place(chunk, prefab, lane, y, z): it makes the prefab at chunk.position + new Vector3(lane * laneWidth, y, z) with prefab.transform.rotation, as a child of the piece.
Write Fill and Clear as above.
Call Fill(chunk) for each piece in Start, and Clear(chunk); Fill(chunk); when a piece goes to the front.

Try it yourself

using UnityEngine;

public class Runner : MonoBehaviour
{
    public float laneWidth = 2.5f;
    public float laneSpeed = 16f;
    public float jumpHeight = 1.6f;
    public float gravity = -40f;
    public float slideTime = 0.7f;

    public int lane;

    private CharacterController controller;
    private float fallSpeed;
    private float slide;

    void Start()
    {
        controller = GetComponent<CharacterController>();
    }

    void Update()
    {
        if (Input.GetKeyDown(KeyCode.A) || Input.GetKeyDown(KeyCode.LeftArrow)) lane = Mathf.Max(-1, lane - 1);
        if (Input.GetKeyDown(KeyCode.D) || Input.GetKeyDown(KeyCode.RightArrow)) lane = Mathf.Min(1, lane + 1);
        bool jump = Input.GetKeyDown(KeyCode.W) || Input.GetKeyDown(KeyCode.UpArrow) || Input.GetKeyDown(KeyCode.Space);
        if (jump && controller.isGrounded)
        {
            fallSpeed = Mathf.Sqrt(jumpHeight * -2f * gravity);
            StopSlide();
        }
        if ((Input.GetKeyDown(KeyCode.S) || Input.GetKeyDown(KeyCode.DownArrow)) && controller.isGrounded)
        {
            slide = slideTime;
            Resize(0.5f);
        }

        if (slide > 0f)
        {
            slide -= Time.deltaTime;
            if (slide <= 0f) StopSlide();
        }

        if (controller.isGrounded && fallSpeed < 0f) fallSpeed = -2f;
        fallSpeed += gravity * Time.deltaTime;

        float targetX = lane * laneWidth;
        float x = Mathf.MoveTowards(transform.position.x, targetX, laneSpeed * Time.deltaTime);
        Vector3 move = new Vector3(x - transform.position.x, fallSpeed * Time.deltaTime, 0f);
        controller.Move(move);
    }

    void StopSlide()
    {
        if (transform.localScale.y < 1f) Resize(1f);
        slide = 0f;
    }

    void Resize(float height)
    {
        controller.enabled = false;
        transform.position += Vector3.up * (height - transform.localScale.y);
        transform.localScale = new Vector3(1f, height, 1f);
        controller.enabled = true;
    }
}