Unity draws the trajectory of pinball and billiards

design sketch

I don't say much nonsense , Go straight to the renderings

principle

The principle is to create a trackball , In the second scene, simulate the physical trajectory of the white ball , And record the track ！ That is to create an invisible scene , Used to simulate the trajectory drawing of the ball .

After the collision , Draw the motion trajectory of the impacted object Transfer momentum to the collision object , Get the object of collision . So as to record the motion trajectory of the collided object

scene

Physics For physical scenes ,GoBallList Used to store the small ball to be reflected ,TrackBallTransform For the trackball to be simulated

Code

There are two key codes ：

call physicsScene.Simulate(0.02f); Complete trajectory prediction ;

This API need Physics.autoSimulation = false;// close physical simulation  

The specific code is as follows ：

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using TMPro;
using UnityEngine;
using Lean.Touch;
using DG.Tweening;
using UnityEngine.SceneManagement;

public class BallPool : MonoBehaviour
{       
    public List<GameObject> GoBallList = new List<GameObject>();// All the reflection balls 
    public Transform trackBallTransform;// trackball （ That is, a small ball that needs physical simulation ）
    private Rigidbody2D trackBallRigidbody;// The rigid body of the trackball 
    private PhysicsScene2D physicsScene;       // Physical scenes 
    public Vector3 vecBallPoint;// The position of the trackball     

    private void Start()
    {
        CreateBallReflect();// Create a reflection ball 
        CreatePhysicsScene();// Create a scene for simulation 
    }

    private void OnEnable()
    {
        LeanTouch.OnFingerDown += OnFingerDown;
        LeanTouch.OnFingerSet += OnFingerSet;
        LeanTouch.OnFingerUp += OnFingerUp;
    }    

    private void OnDisable()
    {
        LeanTouch.OnFingerDown -= OnFingerDown;
        LeanTouch.OnFingerSet -= OnFingerSet;
        LeanTouch.OnFingerUp -= OnFingerUp;
    }

    // Create a reflection ball 
    private void CreateBallReflect()
    {
        // Create trackball 
        trackBallTransform = ObjectPool.Instance.Spawn("BallTrack", LobbyCtrl.Instance.transform.parent).transform;
        trackBallTransform.name = "TrackBall";
        trackBallTransform.position = vecBallPoint;
        trackBallRigidbody = trackBallTransform.GetComponent<Rigidbody2D>();
        UIHelper.SetActive(false, trackBallTransform);

        // establish 20 A white reflection ball , And hide 
        for (int i = 0; i < 20; i++)
        {
            GameObject ball = ObjectPool.Instance.Spawn(Const.Prefab_Obj_BallReflect, transform);
            ball.name = "BallReflect";
            GoBallList.Add(ball);
        }
        for (int i = 0; i < GoBallList.Count; i++)
        {
            UIHelper.SetActive(false, GoBallList[i]);
        }
    }

    // Create a scene for simulation 
    private void CreatePhysicsScene()
    {
        var scene = SceneManager.CreateScene("Physics");
        physicsScene = scene.GetPhysicsScene2D();
        // Move the trackball into the physical scene 
        SceneManager.MoveGameObjectToScene(trackBallTransform.gameObject, scene);
        
    }   

    private void MoveFinger(LeanFinger finger)
    {        
        // Show trackball 
        UIHelper.SetActive(true, trackBallTransform);
        // close   Physics 
        Physics2D.autoSimulation = false; 
        // Each move requires resetting the position and force of the trackball 
        trackBallTransform.position = ballCtrl.transform.position;
        trackBallRigidbody.velocity = Vector3.zero;

        Vector2 screenPoint = Camera.main.ScreenToWorldPoint(finger.ScreenPosition);
        var dir = (screenPoint - (Vector2)ballCtrl.transform.position).normalized;
        // Let the trackball start the physical simulation 
        trackBallRigidbody.AddForce(dir * Const.BallSpeed);

        for (int i = 0; i < GoBallList.Count; i++)
        {
            GameObject ball = GoBallList[i];
            UIHelper.SetActive(true, ball);
            physicsScene.Simulate(0.02f);// It must be added that , The smaller the value, the smaller the spacing of white reflection balls 
            ball.transform.position = trackBallTransform.position;// All white reflection balls will be placed where the trackball passes 
        }
    }

    // Press down 
    private void OnFingerDown(LeanFinger finger)
    {                
        MoveFinger(finger);
    }

    // Move 
    private void OnFingerSet(LeanFinger finger)
    {       
        MoveFinger(finger);
    }

    // Release 
    private void OnFingerUp(LeanFinger finger)
    {        
        // Open Physics 
        Physics2D.autoSimulation = true;        
    }

    // Recycle Pinball 
    void ClearBallList()
    {        
        UIHelper.SetActive(false, trackBallTransform);
        for (int i = 0; i < GoBallList.Count; i++)
        {
            ObjectPool.Instance.Unspawn(GoBallList[i]);
        }
    }   
    
}