Physics2D.Raycast distance

[behdadsoft]

Hi.

I wrote this following code for detect collision between player and enemy when distance is 0.2f.
I want the Ray collision to occur only when the distance between the player and the enemy is 0.2. That is, if this distance is less or more, the collision will not be done.

var hit = Physics2D.Raycast(transform.position, child.transform.position, 0.2f, 1 << LayerMask.NameToLayer("Player"));

How can this be done?

[Kurt-Dekker]

You would need to do two checks, giving slightly-different values on either side of 0.2f, and see which ones hit.

If both hit or if both miss, the object is either too close or too far.

Keep in mind the distance will almost certainly never actually be 0.2f.

Floating (float) point imprecision:

Never test floating point (float) quantities for equality / inequality. Here’s why:

https://starmanta.gitbooks.io/unitytipsredux/content/floating-point.html

Debug.Log(2000.0f * 000.1f); is 200

Now that you have had your coffee, don't forget about floating point imprecision: // @kurtdekker: don't forget about floating point imprecision using UnityEngine; public class FloatingPointImprecision : MonoBehaviour { void Start () { float a = 2000.0f; float b = 0.1f; float product = (a * b); float answer = 200; Debug.Log( "a = " + a); Debug.Log( "b = " + b); Debug.Log( "product of a*b = " + product); Debug.Log( "answer …

Why Doesn't This Code Work?

This will explain it all. In an IEEE single-floating point number you can represent certain numbers perfectly and unambiguously. For instance, 0.5f is precisely represented as 0x3f000000 However, 0.1f CANNOT be precisely represented. One possible approximate representation is 0x3DCCCCCD The analogy is that you cannot show 1/3rd precisely as a decimal. 0.33 is correct to 2 decimal places 0.3333 is correct to 4 places etc. But you can never exactly represent 1/3rd as a decimal numeral. Yo…

“Think of [floating point] as JPEG of numbers.” - orionsyndrome on the Unity3D Forums

[MelvMay]

@behdadsoft

I wrote this following code for detect collision between player and enemy when distance is 0.2f.

Look at the docs, the 2nd argument is not a world position, it’s a direction.

If you want to detect contacts between two points then you use Physics2D.LineCast.

It’s not clear if you’re interested in the distance between potential contacts or not because a ray from the player position to an enemy position would give you the distance from the player center to a contact which is an odd arbitrary value. Why not just use the distance i.e. magnitude of the vector (enemy position - player position)?

Alternately, use Physics2D.Distance, Collider2D.Distance, Rigidbody2D.Distance to ask what the nearest contact points are and use the distance between those which is accurate if you need it.