How to place objects by swipe your finger across the screen?

问题

Using this tutorial we can place objects on the surface by finger tap.

How can we change the script to place objects while swiping a finger across the screen, so that placing objects would be like "painting" area where they should be placed?

Here is the script for placing from the tutorial:

using UnityEngine;
using System.Collections;

public class KittyUIController : MonoBehaviour
{
    public GameObject m_kitten;
    private TangoPointCloud m_pointCloud;

    void Start()
    {
        m_pointCloud = FindObjectOfType<TangoPointCloud>();
    }

    void Update ()
    {
        if (Input.touchCount == 1)
        {
            // Trigger place kitten function when single touch ended.
            Touch t = Input.GetTouch(0);
            if (t.phase == TouchPhase.Ended)
            {
                PlaceKitten(t.position);
            }
        }
    }

    void PlaceKitten(Vector2 touchPosition)
    {
        // Find the plane.
        Camera cam = Camera.main;
        Vector3 planeCenter;
        Plane plane;
        if (!m_pointCloud.FindPlane(cam, touchPosition, out planeCenter, out plane))
        {
            Debug.Log("cannot find plane.");
            return;
        }

        // Place kitten on the surface, and make it always face the camera.
        if (Vector3.Angle(plane.normal, Vector3.up) < 30.0f)
        {
            Vector3 up = plane.normal;
            Vector3 right = Vector3.Cross(plane.normal, cam.transform.forward).normalized;
            Vector3 forward = Vector3.Cross(right, plane.normal).normalized;
            Instantiate(m_kitten, planeCenter, Quaternion.LookRotation(forward, up));
        }
        else
        {
            Debug.Log("surface is too steep for kitten to stand on.");
        }
    }
}

回答1:

Instead of spawning a kitten when the touchphase ends, you can spawn them whenever the touch moves: TouchPhase.Moved. Be warned - this will spawn A LOT of kittens while you drag since this is being checked every frame while in the Update() method. Consider adding a time delay, or only spawning after the finger moves a certain distance.

    void Update ()
    {
        if (Input.touchCount == 1)
        {
            // Trigger place kitten function when single touch moves.
            Touch t = Input.GetTouch(0);
            if (t.phase == TouchPhase.Moved)
            {
                PlaceKitten(t.position);
            }
        }
    }

A distance check could be implemented like so:

float Vector3 oldpos;

void Update ()
{
    if (Input.touchCount == 1)
    {
        Touch t = Input.GetTouch(0);
        if (t.phase == TouchPhase.Began)
        {
            oldpos = t.position; //get initial touch position
        }
        if (t.phase == TouchPhase.Moved)
        {
            // check if the distance between stored position and current touch position is greater than "2"
            if (Mathf.Abs(Vector3.Distance(oldpos, t.position)) > 2f)
            {
                PlaceKitten(t.position);
                oldpos = t.position; // store position for next distance check
            }
        }
    }
}

来源：https://stackoverflow.com/questions/45375087/how-to-place-objects-by-swipe-your-finger-across-the-screen