Is it better to use colliders or a function? (2D game)

Questions & Answers
1

I wrote a script which checks to see if a moving object would get hit by a projectile launched from a stationary object based on the velocities, initial positions, and angles of the given objects when the mouse is clicked rather then using 2D colliders and checking for collisions. I was hoping that by doing this the processing would be decreased since it isn’t checking frame by frame rather only when the mouse is clicked. I am wonder whether or not this is actually the case. I am planning on making a game which will have many moving objects (anywhere from 1 to 30+) and want it to be able to be run on mobile devices and am not sure how much having many colliders effects processing vs a mathmatical computation.

Code I wrote:

using UnityEngine;
using System.Collections;

public class Meteor : MonoBehaviour {
	public float halfSpriteLength;
	private float Ax;
	private float By;
	public float speed = 8;
	private float x;
	public Rotation rotation;
	public float t;
	private float tx;
	private float ty;
	private float X;
	private float X1;
	private float X2;
	private float Xi1;
	private float Xi2;
	private float Xe1;
	private float Xe2;
	private Rigidbody2D rigid;
	private float Speed;
	public float R;

	// Use this for initialization
	void Start () 
	{
		
		rigid = GetComponent<Rigidbody2D> ();
		rigid.velocity = transform.right * speed;
		Speed = GameObject.Find("Barrel").GetComponent<Rotation>().speed;
		rotation = GameObject.Find ("Barrel").GetComponent<Rotation> ();
	}
	
	// Update is called once per frame
	void Update () 

{
	R = rotation.rotZ;
	x = rigid.transform.eulerAngles.z;
	if (Input.GetKeyDown(KeyCode.Mouse0))
	{
		Check ();
		if (transform.position.x < 0) 
		{
			if (x + 180 < R) 
			{
				if ((R < Xi2 && R > Xe2)) 
				{
					Destroy (gameObject, t);
				}
			}
			if (x + 180 > R) 
			{
				if ((rotation.rotZ > Xi2 && rotation.rotZ < Xe2)) 
				{
					Destroy (gameObject, t);
				}
			}
		}
		if (transform.position.x > 0) {
			if (x + 180 > R) {
				if ((R < Xi1 && R > Xe1)) {
					Destroy (gameObject, t);
				}
			}
			if (x + 180 < R) {
				if ((rotation.rotZ > Xi1 && rotation.rotZ < Xe1)) {
					Destroy (gameObject, t);
				}
			}
		}
	}

}
void Check ()
	{
	float Ai = transform.position.x;
	float Bi = transform.position.y;
	float Ci = (-Bi * rigid.velocity.x + Ai * rigid.velocity.y)/Speed;
	tx = Mathf.Abs((transform.position.x) / (Speed*Mathf.Cos(R*Mathf.Deg2Rad) - rigid.velocity.x));
	ty = Mathf.Abs((transform.position.y) / (Speed*Mathf.Sin(R*Mathf.Deg2Rad) - rigid.velocity.y));
	if (ty > tx) 
	{
		t = ty;
	} 
	else 
	{
		t = tx;
	}
	X1 = Mathf.Rad2Deg*(Mathf.Acos ((-(Bi * Ci) + Mathf.Sqrt ((Mathf.Pow (Ai, 4)) + (Mathf.Pow (Ai, 2) * Mathf.Pow (Bi, 2)) - (Mathf.Pow (Ai, 2) * Mathf.Pow (Ci, 2)))) / (Mathf.Pow (Ai, 2) + Mathf.Pow (Bi, 2))));
        X2 = Mathf.Rad2Deg*(Mathf.Acos ((-(Bi * Ci) - Mathf.Sqrt ((Mathf.Pow (Ai, 4)) + (Mathf.Pow (Ai, 2) * Mathf.Pow (Bi, 2)) - (Mathf.Pow (Ai, 2) * Mathf.Pow (Ci, 2)))) / (Mathf.Pow (Ai, 2) + Mathf.Pow (Bi, 2))));
	Xi1 = X1 + Mathf.Rad2Deg*(Mathf.Atan2 (halfSpriteLength, (Speed * t))); 
	Xi2 = X2 - Mathf.Rad2Deg*(Mathf.Atan2 (halfSpriteLength, (Speed * t)));
	Xe1 = X1 - Mathf.Rad2Deg*(Mathf.Atan2 (halfSpriteLength, (Speed * t))); 
	Xe2 = X2 + Mathf.Rad2Deg*(Mathf.Atan2 (halfSpriteLength, (Speed * t)));
	}

Input would be apreciated.

2

The question is : do you want to do it yourself and how precise should it be?

Since you are doing it only on event, you may do it yourself. But you could also cast a volume (using Physics2D cast methods) and check the result. With this method, your objects must have a collider but you may deactivate the collisions between them.

3

The only answer to your question is to use the profiler and see. Your logic of performing a calculation only once should of cause yield better performance than checking for collisions every frame. But, in the code above you’ve still got a rigidbody2d attached to this object, which means the physics simulation is having to run every frame anyway. A circle/box collision check on top of that is very unlikely to make any noticeable difference.

Your bigger problem comes from having 30 dynamic objects - do you really need to check every possible collision between every pair of those objects? (what is that, some 435 combinations?)