Collision between two rigid bodies not registering.

Questions & Answers
1

So I’m working out parts of what will eventually be an FPS involving up/down gravity changes for individual objects. I had previously worked out the gravity reversal for an object after it collided with another (the “energy blast” weapon that will change the gravity for enemies and objects) but now I’m trying to work on applying that to the player character and triggering it with a key stroke instead of weapon collision.

What seems to be happening is my test object representing the PC (a cylinder with a rigidbody and mesh collider, parented to a camera) doesn’t seem to be triggering the collision detection with the floor or ceiling (made of blocks of instances of two prefabs: “1st Floor Block” and “2nd Floor Block”).

So, basically, with the code below, when I hit “z” (“P1-SwitchGrav”), the cylinder will rise to the ceiling and “land” there, but when I hit “z” a second time, nothing happens.

The Debug Log prints out “Hit Z!”, “Rising!” & “Reversing!”, followed by 5 “Hit Z!”'s for some reason, but never a “Grounded!” note, which implies to me that the collision part of the code is not working (the reason “Gravity” and “Grounded” variables are public are so I can monitor them while running my test- and they both get set to false when I hit Z, but never revert to true).

So, what am i missing?

Here’s the code:

#pragma strict

public var gravity : boolean = true;
public var grounded : boolean = true;


function Start ()
{

}

function OnCollisionEnter(collision: Collision)
{
	//Check to see if object is on floor or ceiling
	if(collision.gameObject.name == "1st Floor Block" || collision.gameObject.name == "2nd Floor Block")
	{
		grounded = true;
		Debug.Log ("Grounded!");
	}
}

function Update () 
{
	var value = Input.GetButton ("P1-SwitchGrav");
	
	//Check to see if player has shifted their gravity
	if (Input.GetButton ("P1-SwitchGrav"))
	{
		Debug.Log("Hit Z!");
		
		//If gravity is active & object is on floor, disable gravity,
		//indicate object is not on floor & start to reverse gravity
		if (this.gravity == true && this.grounded == true)
		{
			Debug.Log("Rising!");
			this.gravity = false;
			this.grounded = false;
			this.rigidbody.useGravity = false;
			ReversedGravity();
		}
		
		//If gravity is disabled & object is on ceiling, reactivate gravity
		//& indicate object is not on ceiling
		if (this.gravity == false && this.grounded == true)
		{
			Debug.Log("Falling!");
			this.gravity = true;
			this.grounded = false;
			this.rigidbody.useGravity = true;
		}
	}

}

function ReversedGravity ()
{
	Debug.Log("Reversing!");
	
	//When gravity is disabled, apply constant force towards ceiling
	while (this.gravity == false)
	{
		rigidbody.AddForce(0, 2 , 0);
		yield;
	}
}
2

The first thing I would do is put output inside your OnCollisionEntered() block, but outside of the collision.gameObject.name check, just to see whether you are in fact hitting anything at all. If you are, then perhaps you’ve got the gameObject’s name wrong?

3

Turns out that was kinda the case- looks like my mistake was specifying the name of the prefab when the collision is looking at the name of the instances (I numbered each block instance “1st Block 1”, “1st Block 2”, etc)). To fix it, I used a name.Contains to target the portion of the block instance names that were uniform like this:

if(collision.gameObject.name.Contains ("1st Floor Block") || collision.gameObject.name.Contains("2nd Floor Block"))

Thanks for the hint!