One way platform using 2D Colliders?

I know this topic is a bit stale and I'm pretty new to Unity and Physics2D.IgnoreLayerCollision probably has been added not so long ago, but I solved one way platform with just one line in FixedUpdate().

Physics2D.IgnoreLayerCollision (playerLayer, platformLayer, rigidbody2D.velocity.y > 0);

I solved it by setting the platform's collider to trigger and it's tag to "OneWayPlatform" and then adding the script below to the Player.

What the script does is in OnTriggerEnter/Stay, if the player is above the platform and moving downwards, it stops the player, and stores and disables it's gravity.

Then, once the player exits this particular collider by going left/right, it sets it's gravity back.

Edit: I optimized the code a bit and also increased the readability ;)

Edit 2: Demo: OneWayPlatforms

 #pragma strict
 
 public var deadZone : float = 0.1;
 
 private var g = 0;
 private var touchingPlatforms : int = 0;
 private var body : Rigidbody2D;
 
 function Start () {
     g = rigidbody2D.gravityScale;
     body = rigidbody2D;
 }
 
 function OnTriggerEnter2D (c : Collider2D) {
     if(c.CompareTag("OneWayPlatform")) {

         touchingPlatforms++;

         var maxDistance = (c.transform.localScale.y + transform.localScale.y) / 2;
         if(body.velocity.y < 0 && transform.position.y - c.transform.position.y - body.velocity.y * Time.fixedDeltaTime > maxDistance - deadZone) {
             body.gravityScale = 0;
             body.velocity.y = 0;
             transform.position.y = c.transform.position.y + maxDistance;
         }
     }
 }
 
 function OnTriggerExit2D (c : Collider2D) {
     if(c.CompareTag("OneWayPlatform") && touchingPlatforms-- == 1)
          body.gravityScale = g;
 }

--David

You can use Physics2D.IgnoreLayerCollision and Physics2D.OverlapCircle to achieve one-way platforms.

This script would go on your player game object, with an empty game object placed at the feet of the player, used for the groundCheck transform.

//in your player controller script

 //Now ignore collisions between the Player and OneWayPlatform layers, 
 //unless you're on the ground or travelling up.
 Physics2D.IgnoreLayerCollision( LayerMask.NameToLayer("Player"), 
                                 LayerMask.NameToLayer("OneWayPlatform"), 
                                 !isOnGround || rigidbody2D.velocity.y > 0 
                                );

}

The condition for IgnoreLayerCollision needs both the ground and velocity conditions to prevent the player's position from shifting when passing through the platform.

This assumes you have two layers (Player and OneWayPlatform) defined in Project Settings -> Tags and Layers. I also use EdgeCollider2D components on the one way platforms.

Also, if you wanted to allow the player to fall through the playform if they are holding a down button, you could change your condition to something like: (!isOnGround || rigidbody2D.velocity.y > 0 || Input.GetButton("Down") )

This won't work yet because there isn't a Physics2D.IgnoreCollision yet, but it could be done with multiple layers. Add an EdgeCollider2D at the top. Define its height above the transform of the sprite it's attached to as platformheight.

Then:

 void FixedUpdate () {
         foreach (Rigidbody2D Object in FindObjectsOfType(typeof(Rigidbody2D)) as Rigidbody2D[])
         {
             float lowestpoint = Mathf.Infinity;
             foreach (Transform blah in Object.transform)
             {
                 if (blah.name == "Edge")
                 {
                     if(blah.transform.position.y<lowestpoint) lowestpoint = blah.transform.position.y;  
                 }
             }
             if (lowestpoint > transform.position.y + platformheight)
             {
                 Physics2D.IgnoreCollision(collider2D, Object.collider2D);
             }
         }
     }

Then stick four empty GameObjects called "Edge" on each side of your objects. If you're just using square hitboxes for everything though you can just use lossyscale to work out whether they're above or below. This will make the colliders only work if the object is above the platform.

But, again, Physics2D.IgnoreCollision isn't an option yet, so Physics2D.IgnoreLayer could be used as a temporary fix.

e.g. You could put different platforms on different layers, and then snap the player's height to the layer of the platform he's in, and forbid collisions on the same layer. Which is a pain for now, and a bad idea in general.

But I would also say that just simply using triggers and killing velocity and gravity is a bad idea too - very fast objects will be able to bury themselves into walls and objects will float slightly above your platforms instead of resting on them.

Here is my workaround, because of bug (OnTriggerEnter2D call multiple times, i use 2 triggers, one for OnTriggerEnter, another for OnTriggerExit.

For triggers, i use EdgeColliders and on scene it looks like this

Here is a full prefab structure

This code for enter Trigger

 public class OneWayPlatformTriggerEnterController : MonoBehaviour {
     public int playerLayerId = 8;
     public int enabledPlatformId = 9;
     public int disabledPlatformId = 10;
     GameObject parentGO;
 
     void Start(){
         parentGO = gameObject.transform.parent.gameObject;
     }
 
     void OnTriggerEnter2D(Collider2D other){
         if (other.gameObject.layer == playerLayerId && parentGO.layer == enabledPlatformId){
 
             parentGO.layer = disabledPlatformId;
         }
     }
 }
 

and this for exit

 public class OneWayPlatformTriggerExitController : MonoBehaviour {
     public int playerLayerId = 8;
     public int enabledPlatformId = 9;
     public int disabledPlatformId = 10;
     GameObject parentGO;
     
     void Start(){
         parentGO = gameObject.transform.parent.gameObject;
     }
 
     void OnTriggerExit2D(Collider2D other){
         if (other.gameObject.layer == playerLayerId){
             parentGO.layer = enabledPlatformId;
         }
     }
 }

As you can guess, my player has one layer Id, and oneWayPlatoform has 2 layer, one Layer when platform active and player can walk on it, and another layer which does not interact with player because of switched off in LayerCollision Matrix (Kevin is my player layer)