Bubble – A Bare Bones Introduction to Click and Drag Control

This is a one script proof of concept where you can manipulate a character by dragging it across the screen and avoid the obstacles that are coming towards you.

You can test it out here.

I got the three sprites from the pixabay:

Pufferfish
Bubble.
Underwater

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class FingerScript : MonoBehaviour
{

// Set up a basic scene - just a camera with an orthographic view and a z distance of -10. Drag a background on to the scene if you like. Add 2 GameObjects with sprites to the scene. I have a bubble and a puffer fish so I named them "bubble" and "puffer". Add a RigidBody2D to both and set them to Kinematic. Add a 2D collider to both (I went with a circle colider) and make sure at least one of them has the trigger box checked.

	public Camera myCam;
	public GameObject puffer;
	public GameObject bubble;

// Attach this script to the bubble and drag the above components over to their respective script slots in the inspector. Using a true/false here means that your mouse won't drop the bubble if it is moving too fast...

	public bool dragging = false;
	private float distanceFromCamera = 10f;
	private Vector3 mousePosition;


	void Start ()
	{
//This grabs the Pufferfish and makes it move downwards with a fixed velocity of -5;
		puffer.GetComponent<Rigidbody2D> ().velocity = new Vector2 (0, -5f);
	}

	void Update ()
	{

// You need to update the mouse position constantly and get its co-ordinates in world space instead of janky mouse space.

		mousePosition = myCam.ScreenToWorldPoint (new Vector3 (Input.mousePosition.x, Input.mousePosition.y, distanceFromCamera));

// You can Raycast to see if you are clicking on the bubble. The Input.GetMouseButtonDown (0) is checking if the left mouse button has been clicked.

		if (Input.GetMouseButtonDown (0)) {
			RaycastHit2D hit = Physics2D.Raycast (myCam.ScreenToWorldPoint (Input.mousePosition), Vector2.zero);
			if (hit && hit.collider.name == "bubble") {
				dragging = true;
			}
		}

// This makes the bubble follow the mouse.

		if (dragging) {
			transform.position = new Vector3 (mousePosition.x, mousePosition.y, transform.position.z);
		}

// This stops the bubble from following the mouse if the button is released.

		if (Input.GetMouseButtonUp (0)) {
			dragging = false;
		}

// If the pufferfish goes off the bottom of the screen we just move it back to the top for now. We can pretend like it is a new fish...

		if (puffer.transform.position.y <= -8) {
			MovePufferFishToTop ();
		}
	}
		
// If you collide with the fish it also just makes a new one. Here is where you would loose if you were trying to avoid the fish..

	void OnTriggerEnter2D (Collider2D col)
	{
		if (col.gameObject == puffer) {
			MovePufferFishToTop ();
		}
	}

// this quick code moves the pufferfish back to the top and randomises the x position so it appears in different places.

	void MovePufferFishToTop ()
	{
		float randomx = Random.Range (-6, 6);
		puffer.transform.position = new Vector3 (randomx, 8, puffer.transform.position.z);
	}
}