An object has a trigger and its purpose, when an object is present, performed an action, and if there are no objects, another action
OnTrigger does not work, as it works on contact
You can subscribe to the following messages:
OnTriggerEnter: OnTriggerEnter is called when the Collider other
enters the trigger.
OnTriggerExit: OnTriggerExit is called when the
Collider other has stopped touching the trigger.
Proceed as follows:
From OnTriggerEnter, add the object that entered to a list(*)
From OnTriggerExit, remove the object that left from that list.
Then at any time, the list will contain every element that's inside the trigger.
From Update, do your action depending on whether the list is empty or not.
Note: I'm using the term « list » as in « collection of your choice ». It makes sense to use a HashSet<> rather than a List<> if the trigger can overlap with a significant number of objects.
EDIT: I see your question mentions "Unity 2D". If that means you just need 2D collisions, consider using Collider2Ds, and its 2D counterparts to the aforementioned hooks OnTriggerEnter2D and OnTriggerExit2D
Related
I have a class CollisionHandler which has the OnCollisionEnter method. Each collideable entity in the game has CollisionHandler as a component. So, when 2 objects collide the OnCollisionEnter method is called twice and it's ok because the damage and other things are processed as a result of touching object "B" by object "A" and vice versa.
In addition, each collision creates a flash effect and plays a sound of impact and of course, these effects are also played twice for each collision. Although it wouldn't be imperceptible to the player it doesn't seem to be correct anyway. In order to prevent it, I came up with the following solution: I save the current frame number in another collision participant so it will know that these effects have been played already by the first one.
private void OnCollisionEnter(Collision collision)
{
// Calculate the damage caused by `this.gameObject` to `collision.gameObject`.
// ...
// Play an impact sound and show a visual effect.
if (thisObject.CollisionFrameId != Time.frameCount)
{
otherObject.CollisionFrameId = Time.frameCount;
// play sound
// show hit effect
}
}
Although it works I'm not sure (I'm a novice in Unity) that it's the best practice and if so please suggest other possible solutions.
Note that I didn't ask "Why is OnCollisionEnter getting called twice?". I know why it happens. My question is about the other, though it does mention the name of the same function it still doesn't asks the same.
You could do a GetComponent on the other object with one of your scripts (or the same script) and set the RecentCollisionObject to the current script or gameObject (and maybe a given time frame just for additional safety (if only one triggers it, but not the other for some reason)).
On each collision you check if RecentCollisionObject is the other object (and if no more than ~0.01 seconds has passed). If true, you know that particular collision must already have been processed by the other object just now, so reset all values from that other object and do nothing else. So the next collision which occurs, no matter how soon, will do this cycle anew and work as expected.
This way you let only the first to trigger the collide code execute your code (like a sound). The point is that both collision events are ran in the same frame, so no matter which triggers first, you can prevent the second from running.
You can use the Unity Tag System, you tag action to occur when colliding with that specific tagged object.
As example:
internal void OnTriggerEnter(Collider other) {
if (other.gameObject.tag == "Oject Tag") {
this.GetComponent<AudioSource> ().PlayOneShot (objectTagSoundClip);
}
Just need a audio to play placed in game object.
Maybe you have 2 Colliders. If so you could check if boxcollider for example is colliding only. You could also try on Collision leave. Hope it helps.
like what i have in Question , I know it's something simple and there is a question like this but not enough to solve that confusion,my work flow was: A & B are 2 GO , A has a collided with trigger unchecked , B has a collider with trigger checked i use the OnTriggerEnter2D(Collision collision) function in the A GO to Check if B (collision) touch A GO, i was working with that until now when i discovered that also it works when i used the OnTriggerEnter2D(Collision collision) function in the B script to check if it's touched with A GO even that A hasn't trigger checked.
So does just i need to check on trigger in one of them (A or B) to use the OnTriggerEnter2D() function in anyone ?
So does just I need to check on trigger in one of them (A or B) to use
the OnTriggerEnter2D() function in anyone ?
Yes, just one of them. You can also enable it on both of them. Doesn't really matter.
This is confusing to those new to Unity.
When any type of collision callback function such as OnTriggerEnter2D and OnCollisionEnter2D are called, both of the GameObject involved in the collision will have the callback functions called.
It doesn't matter which one has IsTrigger set to true. As long as one has is trigger, both will have OnTriggerEnter2D called on them if there is a script that implements the callback function. The-same thing applies to OnCollisionEnter2D. When OnCollisionEnter2D or OnTriggerEnter2D is called on one Object, it will also be called on the other Object invloved in the Collins.
I'm new to unreal engine, I'm trying to add large force to an object with a box collider but after it collide with other object (just another instance) the overlap inside each others and become like one object and moving with each others.
Cab anyone explain their behavior and how i should resolve this?
What happens here is that both objects collide with each other continously. To fix that you could try to deactive the OnOverlap()-Event on either the overlapping Object or the colliding object.
In blueprints you can achieve that by setting the Generate Overlap Events-Variable of one of the colliding static meshes of the overlapping objects to false.
In C++ you could simply remove the dynamic event callback for one of the colliding objects like that:
CollidingComponent->OnComponentBeginOverlap.RemoveDynamic(this, &ACollidingActor::OnBeginOverlap);
Where CollidingComponent is the component of your object, which causes the overlap event to trigger.
Like #Alex said, they overlap with each other, over and over. If you didn't know, you can add breakpoints to your blueprint nodes, just like in your code, by right-clicking a node and select Enable Breakpoint (or smth like that). Your game will stop when reaching it and switch to that exact point in your blueprint. You can then hover over that node and see every variables value going in and out of it.
Hope this helps you learing to use the Unreal Engine.
The Unity Manual describes the order in which the Script functions are called. However, I was wondering if there were any rules regarding the order in which the GameObjects themselves are considered in Unity.
GameObjects are basically the nodes of Unity's scene graph and (assuming the scene itself was the root node) they form a tree. I was wondering if that tree structure imposed any rules on the order in which GameObjects are considered.
As already mentioned, the manual describes that Awake() is always called before Start() which is always called before the first call to Update() and so on. However, these relations in time are (mostly) given in scope of a single script on a single GameObject. I want to know if there is also a rule stating the order in which Start() (or any other method) is called on all the GameObjects in the scene.
Specifically I wanted to know:
Are parents always considered before their children are?
Are siblings considered in the same order they are displayed in the scene graph?
Is Script Execution Order enforced only in scope of a single GameObject, or does it consider all GameObjects?
I built a small test project in Unity which basically consists of a 3x3x3 tree of GameObjects, each having 3 scripts.
I found the following answers:
No. Some GameObjects can be considered before their parents are, while some parents can be considered before their children are. And this order can change when reloading the scene or manipulating the scene graph.
No. Siblings can be updated in any order. This order can change when reloading the scene or manipulating the scene graph.
It is enforced over all GameObjects in the scene. If SEO sets script A to be executed before script B, then all instances of script A will be considered before any instance of script B is. Meaning, all instances of A call their Awake() before any B call their Awake(), then all instances of A call their Start() before any instance of B call their Start() and so on.
I am trying to create a basic spawn sequence- the block must be created, moveDownLeft, and then removeLeft. moveDownLeft and removeLeft work fine on their own when the block is added using self.addChild(block1) previously, however I need to have self.addchild within the sequence.
The only way that I can see to do this is use runBlock, and I looked at this question when I got an error using that: Swift: SKAction.runBlock -> Missing argument for parameter 'completion' in call BUT WHY?
So now I am left with this:
block1.runAction(SKAction.sequence([SKAction.runBlock({ self.addChild(self.block1) }), moveDownLeft, removeLeft]))
And nothing in the sequence works because the block is not created in the first place. Why is this happening?
Your code fragment is too short but it looks like a typical chicken and egg problem.
node can only run actions once it has been added as child and thus becomes part of the scene graph
your node is supposed to run an action that will eventually add itself to the scene graph but it's not in the scene graph yet so it won't run that action
Add the node as child first, then run the action. If you need the node to be inactive for some time, simply set it's visible property to NO for the duration. You kay also ned to change other properties, ie postpone creation of the physics body.