arfoundation-samples/Assets/Scripts/PlaceOnPlane.cs

using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Experimental.XR;
using UnityEngine.XR.ARFoundation;

/// <summary>
/// Listens for touch events and performs an AR raycast from the screen touch point.
/// AR raycasts will only hit detected trackables like feature points and planes.
/// 
/// If a raycast hits a trackable, the <see cref="placedPrefab"/> is instantiated
/// and moved to the hit position.
/// </summary>
[RequireComponent(typeof(ARSessionOrigin))]
public class PlaceOnPlane : MonoBehaviour
{
    [SerializeField]
    [Tooltip("Instantiates this prefab on a plane at the touch location.")]
    GameObject m_PlacedPrefab;

    /// <summary>
    /// The prefab to instantiate on touch.
    /// </summary>
    public GameObject placedPrefab
    {
        get { return m_PlacedPrefab; }
        set { m_PlacedPrefab = value; }
    }
    
    /// <summary>
    /// The object instantiated as a result of a successful raycast intersection with a plane.
    /// </summary>
    public GameObject spawnedObject { get; private set; }

    void Awake()
    {
        m_SessionOrigin = GetComponent<ARSessionOrigin>();
    }

    void Update()
    {
        if (Input.touchCount == 0)
            return;

        var touch = Input.GetTouch(0);

        if (m_SessionOrigin.Raycast(touch.position, s_Hits, TrackableType.PlaneWithinPolygon))
        {
            // Raycast hits are sorted by distance, so the first one
            // will be the closest hit.
            var hitPose = s_Hits[0].pose;

            if (spawnedObject == null)
            {
                spawnedObject = Instantiate(m_PlacedPrefab, hitPose.position, hitPose.rotation);
            }
            else
            {
                spawnedObject.transform.position = hitPose.position;
            }
        }
    }

    static List<ARRaycastHit> s_Hits = new List<ARRaycastHit>();

    ARSessionOrigin m_SessionOrigin;
}