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How to check Collision detection for GameObjects of same prefab (Unity)

(For 2D Project)
I created a gameObject and made it a prefab.
Now when the game starts, the prefab is used to instantiate gameObjects and they all should check if they collide with one another.
I tried other unity's collision methods but it didn't work.
They either kept colliding with themselves (their own rigidbody) or it didn't work at all.
I'm new to unity and learning things. I searched every where but didn't get my question solved. I'll appreciate any help, Thank you!
Prefab is loaded and Instantiated as such..
GameObject tile = Instantiate(Resources.Load("Prefabs/Tile") as GameObject);
Its a basic gameObject having SpriteRenderer 2D.
I used Box Collider 2D and Rigidbody 2D components on that prefab -
Inspector
A simple script which has OnTriggerEnter2D(Collider2D other) function to check if it collides..
using UnityEngine;
public class TileCollider : MonoBehaviour {
public Rigidbody2D triggerBody;
void OnTriggerEnter2D(Collider2D other) {
if (triggerBody == null)
return;
if (other.attachedRigidbody == triggerBody) {
Debug.Log("Collision!");
}
}
}
I tried it without any if statements - It triggers collision for the Rigidbody2D of the gameObject (itself)
I passed the Prefab itself to check the collision for - Script in Inspector.
This is where were things get bad. It looks for the rigidbody of its own gameObject but I wanted it to search for other cloned gameObjects from same prefab.

The first thing to look at to solve the problem is to check if your prefabs have tags attached to them.

Assuming you have the TileCollider script attached on your prefab which it looks like it is in the inspector, you are checking if the other.attachedRigidbody is its own rigid body (triggerBody). And an object cannot collide with itself. You should probably check if its own rigid body is not the other.attachedRigidbody. If its not its own rigidbody then you have collision with another GameObject!
I hope I understood your question correctly, Thanks!

There looks to be quite a few errors with your code. First, you've got a triggerBody but it doesn't look like it's assigned. Hopefully you're assigning this manually as part of the prefab arrangement, but you could guarantee this by doing that hookup in Start and throwing an error if it fails to get the Rigidbody, like:
public Rigidbody2D triggerBody;
void Start()
{
if(triggerBody == null) // Would happen if it's not set in the prefab
{
triggerBody = gameObject.GetComponent<RigidBody2D>();
}
if(triggerBody == null) // Would happen if there is no Rigidbody2D attached at all!
{
Debug.LogErrorFormat("Failed to find a Rigidbody2D to use with {0}!", gameObject.name);
}
}
Another issue is that you're asking for collisions, but your code is looking for triggers. Here's a link to an article, but the short version is that if you're checking OnTriggerEnter then at least one of the colliders involved needs to have the IsTrigger option ticked:
Another issue is that you're bailing on the operation if the triggerBody is null. As I mentioned at the start, you're not explicitly setting the triggerBody in your code, so if it's also not set in the prefab then you'd abort here even if the collider options were set correctly.
Finally, and probably most importantly, is this snippet doesn't make sense:
if (other.attachedRigidbody == triggerBody) {
Debug.Log("Collision!");
}
What you're saying here is that you want there to be a collision if the other rigidbody is the same as the local rigidbody. This would ensure the behavior you described in your post,
They either kept colliding with themselves (their own rigidbody) or it didn't work at all.
You're only calling it a collision if they're colliding with themselves! The way to check if it's NOT self-colliding is to make sure the other.attachedRigidbody is NOT equal to the local triggerBody!
What you would want instead would be:
if (other.attachedRigidbody != triggerBody) {
Debug.Log("Collision!");
}

unity text trigger not working as expected

in my game im trying to make text appear on the ui when entering a specific room,but when i try to go into that room nothing happens
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
public class Room_trigger : MonoBehaviour
{
public GameObject UiObject;
public GameObject cube;
void Start()
{
UiObject.SetActive(false);
}
void OnTriggerEnter(Collider other)
{
if (other.tag == "player")
{
UiObject.SetActive(true);
}
}
void Update()
{
}
void OnTriggerExit(Collider other)
{
UiObject.SetActive(false);
Destroy(cube);
}
}
the player controller is based of of brakeys fps controller tutorial.

Three things you will need to check:
Does the player object (the one that the player capsule collider component is attached to) have the tag "player" assigned to it? Is it definitely "player" and not "Player" or "Player1". Note - the TAG of an object is not the same as the NAME of an object.
Is the "Is Trigger" on the capsule collider on the player object ticked/checked? If the player capsule collider is not a trigger then it won't cause OnTriggerEnter to be fired by your Room_trigger attached object. Also check the next point.
If you don't want your player capsule collider to be a trigger (which is highly likely), then make sure that the object your Room_trigger script is attached to has:
a collider that is set to Is Trigger
a Rigidbody component
A couple of other possibilities are that you haven't dragged GameObjects into the UiObject and/or cube fields in the Unity Editor UI but that should throw NullReference errors in the console when you run the game.
Whilst Vasmos is correct, you should compare strings using the Equals() method, that's not going to be the cause of your trouble in this specific case. Comparing strings using == as you've done here will work.

replace
if (other.tag == "player")
with
if (other.tag.Equals("player"))
always use .Equals for comparing strings, otherwise its just comparing if its the same variable

#HumanWrites i figured out what the problem was, the cube wasn't set as trigger, the i watched a different tutorial and he sayed "dont forget to set the collider as trigger" and that fixed it.

My projectiles wont collide with my enemies in a 2D side scrolling Unity project?

As the title suggests, I've literally just started learning Unity recently and I'm practising by making a side scrolling shooter. I've been following a Udemy course about it and (to my knowledge) I've been following the tutor's instructions to the letter, but at the point where he tests his and it works fine, by projectiles go straight through my enemies.
I'm a bit stumped at this point and so I thought I'd post here to see what you guys thought. I bet it's something really simple I've not done.
Please see my projectile code below:
using UnityEngine; using System.Collections;
public class DestroyEnemyAndProjectile : MonoBehaviour {
public GameObject WhiteExplosion;
public GameObject OrangeExplosion;
void Start()
{
}
void Update()
{
}
void OnCollisionEnter2D (Collision2D tempCollision)
{
if (tempCollision.gameObject.tag == "Collision")
{
spawnParticles(tempCollision.transform.position);
Destroy(tempCollision.gameObject);
}
}
void spawnParticles(Vector2 tempPosition)
{
Instantiate(WhiteExplosion, tempPosition, Quaternion.identity);
Instantiate(OrangeExplosion, tempPosition, Quaternion.identity);
}
}
Thanks for your help!
I did post a question to them which got a response, they suggested that perhaps the projectile is going too fast and check there was a Rigidbody 2D attached - both of which were already collect

make sure that the object you're colliding with has the tag "Collision", with the same capitalisation.
If it's not, you can do this by:
1. Selecting the GameObject to be collided with
2. In the top-right, select the Tag property
3. Add tag, click the plus and type in "Collision"
4. Select the GameObject again, and select the "Collision" tag from the Tag property dropdown
Otherwise, if that's not the issue. Make sure the projectile has a type of Collider2D component, and that the projectile, or the object being collided with, has a Rigidbody2D.

First I would like to know what the behaviour of this script curently is. Is the collision method being called, and the projectile goes through the enemy anyway? Or the collision method is not being called at all?
That being said, these are things that you should check in order for collision to work:
Make sure that the projectile and the enemy have Collider2D components attached to them.
Make sure that the projectile and/or the enemy (at least one of them must) have a Rigidbody2D attached to it.
Make sure that the layer of the projectiles and the layer of the enemies are set to collide in the collision matrix (You can find the collision matrix in Edit->ProjectSettings->Physics)
Make sure that the enemy GameObject has its tag set to "Collision".
P.S: Welcome to Unity where issues like this are, in fact, usually caused by something super simple that you probably missed.

Find and add the velocity of a Rigidbody that's directly below another? (Unity + C#)

I have an issue that I've not been able to solve for a few days now and without it working I can't move on with my project, so your help would be greatly appreciated!
What I'm trying to do is 'find' the velocity of an object that is directly below my 2D sprite (that also contains a Rigidbody and 2D box collider) and then add that velocity (in the same direction) to the object that is 'looking' for it.
I feel like ray-casting might be part of the answer but I'm not sure how to use that, especially in this context.
The idea behind this is I have a platform that can carry objects stacked on top of each other, so you move the mouse, it manipulates the platforms velocity, but this causes the objects on-top to fly backwards, no mater how high the friction is.
Here is the platform code:
void Update()
{
float distance_to_screen = Camera.main.WorldToScreenPoint(gameObject.transform.position).z;
Vector3 pos_move = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, distance_to_screen));
mouseDelta = pos_move - lastMousePosition;
acceleration = mouseDelta.x * 0.4f;
platformVelocity += acceleration;
platform.velocity = new Vector2(platformVelocity, 0) * speed;
lastMousePosition = pos_move;
}
Thank you for taking the time to read this, I would very much appreciate any help you can give!

Is it necessary to 'find' that object? 'Finding' may be difficult & costing.
Can you hold the 'below-thing' reference and pass it to 'above-thing'?

I'm assuming you have some method on objects that checks whether it's on a moving platform. One option is to add an IsOnMovingPlatform flag on those objects. Then use a similar method to check if any object is on top of the "IsOnMovingPlatform == true" objects. Keep doing passes on that method until you don't come up with any more flags set to true.

So, i'm trying to understand your question and I think I might know what you're talking about.
Are you saying that you want your game object (2d sprite) to stay on the platform as its moving? I have had the same problem, where a platform is moving and my player (game object) slides off- and this is how I fixed it.
Add a box collider to the platform (trigger). When the player enters the platform, make the player's transform the platform. That way, when the platform moves- the player moves with it no matter what the speed is.
For example:
void OnTriggerEnter2D(Collider2d collider){
if(collider.tag.equals("Player")){ // you only want the player to work
// attach script to platform for "this.transform" to work
collider.transform.SetParent(this.transform);
}
}
then, to unparent the transform "otherwise, even when the player is off the platform, it will move with the platform.
void OnTriggerExit(Collider2d collider){
// assuming your player isn't supposed to have a parent!
collider.transform.parent = null;
}
Sorry if I misunderstood your question! If this is what you were going for, finding the velocity of the platform is not necessary. Also, this is uncompiled code- if you have issues let me know.
EDIT:
To add a bit of a give, for the entire duration that the player is in contact with the platform, we can add a little bit of a negative force to shove the player a little bit!
We do this by using OnTriggerStay2D (assuming your game is 2d, otherwise use OnTriggerStay).
For example:
void OnTriggerStay2D(Collider2d collider){
if(collider.tag.equals("Player")){
collider.getComponent<Rigidbody2D>().addForce(new vector2(forceToAdd, 0));
}
}
now, that "forceToAdd" variable should be based on the speed and direction that your platform is going. Does your platform have a rigid body on it? if so you can get your force variable by retrieving the rigid body from the platform (getcomponent()) and get the X velocity from it. With this velocity, experiment with dividing it by numbers until you find a good fit, multiply it by -1 (because you want to push the player in the opposite direction of the platform travel), then this will be your forceToAdd!
However, if your platform is not using a Rigidbody, then a way you can do this is record the x positions in your script (just two positions, and subtract these to find the distance in an update method), multiply by -1, try dividing by a number (experiment with this) and that can be your force to add variable.
Also, my code for the OnTriggerStay2d is rough, the spelling could be a bit wrong- but this will give you a rough idea for a solution! ALSO.. I don't think getting the component of a rigid body should be done in every frame, a way around this would to have your rigid body component as a global variable in the script, then set your rigid body on OnTriggerEnter2d, this way it will only retrieve it once (instead of every frame) which I assume would be more efficient!
Good luck! and if you have any questions il try to help!

This is a raycast2d version, I tested it and it works much better than the trigger collider version :).
using UnityEngine;
using System.Collections;
public class RaycastFeetDeleteLater : MonoBehaviour {
[SerializeField] private float raycastDist = 0.1f;
[SerializeField] Transform feet;
[SerializeField] private float xForceDampener = 0.1f;
private Rigidbody2D rb2d;
// Use this for initialization
void Start () {
rb2d = GetComponent<Rigidbody2D> ();
}
// Update is called once per frame
void FixedUpdate () {
RaycastDown ();
}
private void RaycastDown(){
RaycastHit2D hit = Physics2D.Raycast (feet.position, Vector2.down, raycastDist);
if (hit.collider != null) {
print (hit.transform.tag);
if (hit.collider.tag.Equals ("Platform")) {
transform.SetParent (hit.transform);
Vector2 force = new Vector2 ((hit.transform.gameObject.GetComponent<Rigidbody2D> ().velocity.x * xForceDampener) * -1, 0);
print (force);
rb2d.AddForce (force);
} else if (transform.parent != null) {
print ("UNPARENT");
transform.parent = null;
}
} else {
if (transform.parent != null) {
transform.parent = null;
}
}
Debug.DrawRay (feet.position, Vector3.down, Color.green, raycastDist);
}
}
This script is attached to the player! No need to have scripts on the platforms, which was the main reason my previous method was a pain :P
Basically this script does the following:
- Gets rigidbody2d of the player on start (we will be adding forces to the player with it soon, so might as well store it in a variable!
On FixedUpdate (Different than Update, FixedUpdate is called on Physics update, where as Update is called every frame) I have read that raycast should use FixedUpdate, I suppose because it is a Physics method!
RaycastDown shoots a 2D raycast directly down from the feet position (to get the feet, create a child object of the player, put the position of the feet a tiny bit below the player, NOT ON THE PLAYER- I will explain why in a second why that will mess up everything! Then drag the feet GameObject on to the "feet" slot of the script.)
Raycast shoots from feet directly down at a distance that is changeable in the editor (raycastDist) I found a distance of 0.1f was perfect for my needs, but play around with it for yours! You can actually see a drawing of your Ray by using Debug.DrawRay as seen in the code, the ray is only visible in the editor- not game view! But this will help, especially with positioning the feet.
Checks if it hit an object with a collider, if so check if the objects tag is a Platform (set the platforms to a new tag and call it Platform).
If it hits a platform set the parent of the player to the platform (like the last script) and start applying a little force to the player in the negative direction that the platform is traveling (we get the rigid body of the platform to find its velocity).
If the raycast does not hit a platform, unparent it so the player can move freely.
Thats basically it, however...
Please note:
This script needs to be on the player, not any of the players child objects, since this script will unparent the player from any platforms- if you have the script on a child object of the player it will unparent from the player- which is horrible. So The script MUST be on the root game object of the player. There are ways around this if for some reason you can't.
As mentioned before, the "feet" child object must be a little bit under the player- this is because when the Raycast2d "fires" it will find the FIRST object with a collider it hits- so if you have the start of the raycast hit a collider on the player then it will always show the raycast hitting the player, not a platform. So to get around this have the raycast fire from the feet- and have the feet position a tiny bit below the player. To help with this I added a print statement that will print to the console which object the raycast is hitting, if it doesn't say "Platform" then you need to lower the feet! :)
Furthermore, I'm not sure how you are moving your platforms- but if the Velocity of the platform always prints "0,0" then its because you are moving the platforms position directly, instead of moving it by forces (this happened to me when I was testing this script). I got around this by moving the platform by "AddForce". Also depending on the "Mass" of your platforms, you may need to drastically increase the "xForceDampener" which I should of actually labeled "xForceMultiplier" as I found while testing I needed to set it much higher- like at 60, instead of 0.25 which I previously thought would be okay..
Hope this helped :D
EDIT: Linking the unity docs for 2D Raycasts in case you need
http://docs.unity3d.com/ScriptReference/Physics2D.Raycast.html

AddForce Method Not Working

I am programming a top-down hack-and-slash game for a class. We want a mechanic where if you get hit by an enemy, or an enemy hits you, you get 'knocked back'. Unfortunately, no matter what I have tried, I cannot get either the enemy or the player to react to the force.
Here is a list of things I have checked that have been suggested in other questions like this:
Player/Enemy is NOT Kinematic
Tried with both Gravity on and off
No positions/rotations are frozen
Player/Enemy have Rigidbodies attached
Player/Enemy have colliders attached, one with and one without the 'isTrigger' function checked.
Tried both OnCollisionEnter and OnTriggerEnter
The force value is high, the mass, drag, and angular drag are low
I have run out of ideas. Any and all support you can give is greatly appreciated.
Here is a snippet of the code from a script from the player Object:
public void OnTriggerEnter(Collider col)
{
if (col.gameObject.tag == "EnemyHit" && !invincible)
{
Debug.Log("The player has been hit!");
//sets player as invincible
invincible = true;
// Set the damaged flag so the screen will flash.
hit = true;
timeOfHit = Time.time;
// Reduce the current health by the damage amount.
currentHealth -= 1;
GetComponent<Rigidbody>().AddForce(transform.forward * recoilThrust, ForceMode.Force);
Debug.Log("This is the force that is being added to the player when it is hit. : " + -transform.forward * recoilThrust);
//...
}
}
I can prove (using the Debug.Log) function, that the code reaches there, and the force is calculated.

To summarise the comments:
Rigidbody.AddForce doesn't work when the object has a CharacterController besides the rigidbody. In this case the effect has to be "faked". Possible ways can be found here:
The last couple of posts
Another solution, C# and Javascript
Basically you need to apply the force using CharacterController.Move.

Is Kinematic enabled? Doing so will make the object ignore physic forces.