Is it possible to return the Object that is underneath/in contact with another Object without using hitTestObject ?
I'm wondering if I can remove the need to loop through an array of 'active' Objects and simply get the instance that's underneath at any given time. Possibly using as3 events ?
many thanks SC
You can use the getObjectsUnderPoint() method of the DisplayObjectContainer class.
Be carefully, using a getObjectsUnderPoint().
getObjectsUnderPoint() return types Array. this mean specify Point above all DisplayObjects return. sometimes you do not want to get the value. So the objects in the array must be verified. Faced this problem, especially DisplayObjects when they overlap or if you load the other swf
Related
I was actually looking for a way to pass by reference in AS3 but then it seemed that adobe and lots of people's understanding of pass by reference is different from what I have been taught at the university. I was taught java was pass by value and C++ allowed pass by reference.
I'm not trying to argue what pass by value and reference are. I just want to explain why I'm using pass by object in the question...
Back to the question, I would like to do something like:
public function swapCard(cardA:Cards, cardB:Cards) {
var temp:Cards = cardA;
cardA = cardB;
cardB = temp;
}
...
swapCard(c1, c2);
EDIT: adding two examples on how I'm using the swapCard function
1) in the process of swaping a card between player1 and player2's hand
swapCard(player1.hand[s], player2.hand[t]);
2) in the process of swaping a card between player1's hand and deck
swapCard(player1.hand[s], player1.deck[rand]);
In C++, we only need to add a symbol before the parameters to make it work (and we call THIS pass by reference). But in AS3, cardA and cardB are just pointers to the formal parameters. Here in the function, changing the pointers does not do anything to the formal parameters :(
I have been searching for hours but I couldn't find a way to without knowing all the properties of the Cards.
If I have to change the properties of the cards one by one then maybe I should change swapCard to a static function in class Cards? (because I don't want to expose everything to another class) I'm not sure if this is a good practice either. This is like adding a swap_cars function into class Cars. If I let this happen, what will be next? Wash car, lend car, rent car... I really want to keep the Cards class clean and holds only the details of the card. Is there a possible way to do this properly in AS3?
The kind of swap function that you're trying to implement is not possible in AS3. The input parameters are references to the input objects but the references themselves are passed by value. This means that inside the function you can change the cardA and cardB but those changes will not be visible outside the function.
Edit: I added this portion after you edited your question with sample usage.
It seems like you're trying to swap two objects in 2 different arrays at given array positions in each - you can create a function for this in AS3 but not the way you attempted.
One possible implementation is to pass the arrays themselves and the positions that you're trying to exchange; something like this:
// Assumes arrays and indices are correct.
public function SwapCards(playerHand:Array, playerCardIndex:int,
playerDeck:Array, playerDeckIndex:int):void
{
var tempCard:Card = playerHand[playerHandIndex];
playerHand[playerHandIndex] = playerDeck[playerDeckIndex];
playerDeck[playerDeckIndex] = tempCard;
}
Note that you still exchange references and the arrays themselves are still passed by reference (and the array references are passed by value - you could, if you wanted, change the arrays to new arrays inside this function but you wouldn't see new arrays outside). However, because the array parameters refer to the same arrays inside and outside the function, you can make changes to the contents of the array (or other array properties) and those changes will be visible outside.
This solution is faster than cloning the card because that involves allocating memory for a new Card instance (which is expensive) and that temporary instance will also have to be freed by the garbage collector (which is also expensive).
You mentioned in a comment that you pass cards down to lower levels of code - if you don't have a back reference to the arrays (and the positions of the cards), you will not be able to easily swap cards - in AS3, all input parameters are copies (either the copy of the value for primitive types or the copy of the reference for complex objects - changes to the input parameters in a function will not be visible outside).
EDIT: renaming the function from clone to copyFrom as pointed out by aaron. Seems like clone is supposed to be used as objA = objB.clone()
At this point, I'm adding a copyFrom() function in the Cards class such that
var temp:Cards = new Cards(...);
var a:Cards = new Cards(...);
...
temp.copyFrom(a);
...
temp will be copying everything from a.
public function swapCard(cardA:Cards, cardB:Cards) {
var temp:Cards = new Cards();
temp.copyFrom(cardA);
cardA.copyFrom(cardB);
cardB.copyFrom(temp);
}
I will wait for a week or so to see if there are any other options
You have some good answers already, but based on the comments back-and-forth with me, here's my suggestion (I use "left" and "right" naming because it helps me visualize, but it doesn't matter):
function swapCard(leftCards:Array, leftCard:Card, rightCards:Array, rightCard:Card):void {
var leftIndex:int = leftCards.indexOf(leftCard);
var rightIndex:int = rightCards.indexOf(rightCard);
leftCards[leftIndex] = rightCard;
rightCards[rightIndex] = leftCard;
}
Now you can swap the cards in the two examples you posted like this:
swapCard(player1.hand, player1.hand[s], player2.hand, player2.hand[t]);
swapCard(player1.hand, player1.hand[s], player1.deck, player1.deck[rand]);
However, note that while this swaps the cards in the arrays, it does not swap direct references to the cards in those arrays. In other words:
var a:Card = player1.hand[0];
var b:Card = player2.hand[0];
swapCard(player1.hand, a, player2.hand, b);
// does not change the references a and b, they still refer to the same card
a == player2.hand[0];
a != player1.hand[0];
b == player1.hand[0];
b != player2.hand[0];
Typically, this sort of thing is handled by dispatching a "changed" event so that any code that cares about the state of a player's hand array will know to re-evaluate the state of the hand.
There's a deep misunderstanding going on here. The question is about object reference but the PO is not trying to swap any Object reference at all.
The problem comes from the fact that the PO does not understand the difference between variable and objects. He's trying to swap variable/object reference which is not dynamically possible of course. He wants with a function to make the variable holding a reference to Object A, swap its object reference with another variable. Since Objects can be passed around but not variables (since they are just holders (not pointers)) the task is not possible without a direct use of the given variable.
To resume:
variables are not Objects!
variables hold a reference to an object.
variables cannot be passed in function or referenced in functions because THEY ARE NOT OBJECTS.
I am completing an online tutorial and manipulating it suit my website. I've come across this code...
`// Create a menu item movie clip in the menu_mc instance on the main timeline
// for each item element offsetting each additional further down the screen
var item_mc = menu_mc.attachMovie("movieitem","item"+item_count, item_count);
item_mc._x = item_count * item_spacing;
item_count++;`
The following line gives me a problem (the method is no longer supported)
var item_mc = menu_mc.attachMovie("movieitem","item"+item_count, item_count);
How can i achieve this?
I've tried the following with no joy. message too many arguments?
var mItem:movieitem = new movieitem;
var item_mc = menu_mc.addChild(mItem,mItem+item_count, item_count);
addChild() only accepts 1 argument, which is the display object itself. Also, it looks like you're missing brackets when you create your object and by convention, class names are capitalised.
var mItem:movieitem = new movieitem();
Edit based on my comment
Looking at the documentation for attachMovie() for AS2 (wow, been awhile since I've looked at this), it takes in 3 arguments:
id:String, name:String, depth:Number
Now the id is used to grab a movieclip from the library. This is no longer needed as you've already created a movieclip object from your library in the line before:
var mItem:Movieitem = new Movieitem();
The second argument name is used to create a unique instance name for the created moviclip from the library. You don't really need this. In the line where you create the movieclip (see above), you already have a unique reference you can use to access the movieclip. Interestingly, attachMovie() also returns a reference -I've never ever found a use for the instance names given with the 'name' argument. I just use the reference returned to access it, which you are already doing.
The third argument depth determines which depth the movieclip is placed at. In your case, I am guessing that ' item_count' is just a number that increases, which effectively puts that movie clip at the highest depth when that line is executed. By default, addChild() will automatically do this for you and put the display object (your movieclip) at the highest depth within the parent at the time it is added. So, unless you wanted it at a specific depth/overlapping order, you don't really need to pass this in either. If you did want to add something at a specific depth, look at addChildAt()
Hence as mentioned before, you can just pass in the reference to your movieclip/display object in to addChild().
Are there any general guide lines for using retain and release for objects in cocos2d-X ? When creating objects in a function, is it true that the functions memory is cleaned up the second the function returns. When a object is created, calling the retain function of the object, will retain object beyond the function return ?
Kind Regards
Generally in c++ you have this behaviour:
void foo() {
Object a;
Object *pA = new Object();
(…)
}
This would result in a being destroyed automatically at function end, as it was allocated on stack. The *pA would not get destroyed, as it was allocated on the heap (thus, you only loose the reference to it, but the object itself still lives).
Cocos implements a thing called "Automatic Reference Counting" : each CCObject has a reference counter and two methods retain() and release(). The way this works is, that every time you create an object, it gets registered in cocos structers (CCPoolManager). Then with every frame (between them being drawn) there is a maintenance loop which checks the reference counter of all objects : if it is 0 this means (to cocos) that no other objects reference it, so it is safe to delete it. The retain count of an object is automatically incresead when you use this object as an argument for an addChild function.
Example :
void cocosFoo() {
CCSprite *a = CCSprite::create(…);
CCSprite *b = CCSprite::create(…);
this->addChild(b);
}
What happens here is this :
Two CCSprites are created, cocos knows about them.
The b sprite is added to this object (say a CCLayer)
The function ends, no objects are destroyed (both of them being on heap).
Somewhere between this and next frame, the maintanance gets run. Cocos chcecks both sprites and sees that a has reference count == 0, so it deletes it.
This system is quite good, as you don't need to worry about memory management. If you want to create a CCSprite (for example), but not add it as a child yet, you can call retain() on it, which will raise its reference counter, saving it from automatic deletion. But then you'd have to remember about calling release() on it (for example, when adding it as a child).
The general things you have to remeber about are :
Each call to retain() by you needs to be paired with release().
You generally shouldn't delete CCObjects yourself. If you feel that you need to, there is a conveniece macro : CC_SAFE_DELETE(object)
So to answer your questions in short :
Are there any general guide lines for using retain and release for objects in cocos2d-X ?
Yes, you should generally not need to do it.
When creating objects in a function, is it true that the functions memory is cleaned up the second the function returns.
Answer to this is the whole text above.
When a object is created, calling the retain function of the object, will retain object beyond the function return ?
Yes, as will adding it as a child to another (retained in any way) object.
Here is the thing,
cocos2dx has an autorelease pool which drains the objects which have retain count=0 which is a variable to keep in check the scope of the cocos2dx object.
Now when you create new object using the create method it is already added to the autorelease pool and you don't need to release it or delete it anywhere , its like garbage collector in java, takes care of garbage objects behind your back.
But when you create new object using 'new' you definitely need to release it in its destructor or after its use is over.
Second thing,
when your object is added to the autorelease pool but you need it somewhere else you could just retain it , this increments its retain count by one and then you have to manually release it after its use is over.
Third Thing,
Whenever you add child your object it is retained automatically but you don't need to release it rather you remove it from the parent.
I've just started to learn actionscript for a month or so, and I've been stuck on this part of the code for about 2 days now ><
So basically, I wanted to write a hitTestObject in a movieclip ("fire_mc") to detect if it overlaps the the child I added on stage (enemy)
So here's what I wrote in the main stage...
var newtarget:enemy=new enemy();
stage.addChild(newtarget);
newtarget.x=40;
newtarget.y=30;
and every time I traced the newtarget in the fire_mc, it turns out to be NULL...
So should I be tracing enemy or newtarget? (Cuz I tried both and nothing works).
And how can I hitTestObject in the fire_mc movieclip?
Is it possible for me to hitTestObject newtarget if I were to create multiple newtarget-s?
If not, what should I do?
And can someone tell me the difference between root, and MovieClip(root) (Because sometimes in a movieclip I have to use the former one to work, and sometimes the latter, and I have no idea why cuz I'm all referencing to the same place)
Sorry for these simple and lengthy questions, I'm really just a noob and I tried looking up for answers in the web for hours, but nothing helpful turned up><
Thanks in advance :)
In this statement
var newtarget:enemy=new enemy();
var - keyword used to define varibles, newtarget - variable name in which pointer to new class instance stored, :enemy - data type (the class name), new - keyword used to create new class instances, and finally enemy is class constructor (by the way there is a rule of good manners by which class names are capitalized)
So answer for you question which should you use when you want check is some is overlapping is 'newtarget'.
Now about hit test - all you need do to check if two objects hit each other is correctly use their references from the part of project where your code is writen.
For example if you have your fire_mc on MainTimeline created by IDE, and code of creation of you enemy instance stored in newtarget sameplace, then if you check will be placed in frame of MainTimeline where both object present it will be like this
fire_mc.hitTestObject(newtarget);
or this
newtarget.hitTestObject(fire_mc);
All these statements give you same result - if objects intersect each other you have true returned.
If you created 'newtarget' on MainTimeline and checks will be from fire_mc (which is on MainTimeline to) frame, then code will something like that
this.hitTestObject(MovieClip(root).newtarget);
Now about root. Primarily it is a property of DisplayObject in which reference to the top-most display object in swf-file structure is stored. So as such it is inherited by all child classes. So here's the trick. When you try get your objects in swf structure using root here the differences are based on the fact that root always return object as DisplayObject and that means what if you object contains something that DisplayObject shouldn't you can't get it. So you must convert returned reference to need data-type usign MovieClip(...).
I have a lot of display objects in an array that I'm constantly adding and removing from stage. When removed they are not used anymore.
Considering the displayObject is not on the display list, and has no event listeners... will it be garbage collected if I use splice to remove it from the array?
Is it safer if I null the object first?
myArray[2] = null;
myArray.splice(2,1);
As long as there are no remaining references to the DisplayObject then yes, removing it from the array using splice, or even just setting it to null will allow it to become a candidate for garbage collection.
Update: Setting the item to null before removal from the array is redundant and will make no difference.
If you need better performance I suggest you using pools instead of creating lots of objects and putting them in array. Use some linked list implementation instead of splice() operation, which is really slow.