Click and drag to draw a line from one predetermined point to another

Questions & Answers
1

Hi I’m pretty new to Unity and not sure how to approach this problem.

I’m creating a 2D zip line building simulator/puzzle game for kids: given a set of predetermined “snap points,” a player should be able to draw zip line segments between snap points (by clicking and dragging the mouse from one snap point to another) to create a zip line course. The snap points are given so that the player can only build a zipline between those predetermined points and not just anywhere on the screen. This restriction is where I’m having trouble.

I’ve been able to create snap points as circular-shaped game objects and use the 2D line renderer to draw lines between snap points, but currently I can draw lines anywhere else on the screen too. How can I restrict the drawing of lines (by clicking and dragging the mouse) to only occur between two snap points and no where else on the screen?

2

Note1: Since i am inexperienced with Unity2D, i’ve made this script using a 3d scene. So if this do have a use for you, you only need to adapt it to your 2D project.

Note2: On this scene, a created snaps GOs and assing this script foreach.

Note3: Bare in mind that in this code, the lines do cross another snaps in order to reach their target.

using UnityEngine;
using System.Collections;

public class LineGenerator : MonoBehaviour 
{
	public GameObject emptyGO;
	GameObject instantiatedGO;

	GameObject currentSnap;

	bool phase1;
	
	Vector3 lineWantedPosition;
	
	void Update ()
	{	
		if (Input.GetButtonDown ("Fire1"))
		{
			Ray ray1 = Camera.main.ScreenPointToRay (Input.mousePosition);
			RaycastHit hit1;

			if(Physics.Raycast(ray1, out hit1, Mathf.Infinity))
			{
				if(hit1.collider.gameObject.CompareTag ("Snap")&& hit1.collider.gameObject == this.gameObject)
				{
					currentSnap = hit1.collider.gameObject;
					phase1 = true;
					instantiatedGO = (GameObject) Instantiate (emptyGO, currentSnap.transform.position, Quaternion.identity);  
				}
			}

		}
		if (Input.GetButtonUp ("Fire1"))
		{
			Ray phaseRay = Camera.main.ScreenPointToRay (Input.mousePosition);
			RaycastHit phaseHit;

			phase1 = false;
                instantiatedGO = null;
			currentSnap = null;

			if(Physics.Raycast(phaseRay, out phaseHit, Mathf.Infinity)) 
			{
				if(phaseHit.collider.gameObject == currentSnap || phaseHit.collider.gameObject.tag != "Snap")
				{
					Destroy (instantiatedGO);
				}

			}
		}

		if (phase1 == true) 
		{
                    MouseRayGenerator();
			LinesSpawn();
		}
	}
	

	void MouseRayGenerator()
	{
		if (phase1 == true) 
		{
			Ray mouseRay = Camera.main.ScreenPointToRay (Input.mousePosition);
			RaycastHit mouseHit;
				
			if (Physics.Raycast (mouseRay, out mouseHit, Mathf.Infinity))
			{
				lineWantedPosition = new Vector3 (mouseHit.point.x, mouseHit.point.y, mouseHit.point.z);
			}
		}
	}

	void LinesSpawn ()
	{
		if(phase1 == true)
		{
			LineRenderer line;
			line = instantiatedGO.GetComponent<LineRenderer>();
			line.enabled = true;

			Ray lineRay = new Ray (instantiatedGO.transform.position, lineWantedPosition);

			line.SetPosition (0, lineRay.origin);
			line.SetPosition(1, lineWantedPosition);
		}
	}
}

If this do not fits you, I hope it put you on the right track.