I have noticed a weird behavior of the variables in for loops. It's not really a problem, but it disturbs me a lot.
Actually I've created two loops this way:
for (var i:uint; i<19; i++) SomeFunction (i);
for (var i:uint; i<26; i++) SomeOtherFunction (i);
What I received was a compilation warning:
Warning: Duplicate variable definition.
This warning really surprised me. Nothing like that ever happened to me in other languages.
It seems that the i variable gets into the scope that is higher in the hierarchy and becomes available out of the loop's block. I've also tried to embrace the loop block in a curly brace, but it didn't change anything.
Why does it happen? Is it normal? Is it possible to avoid it? For now I've just set different names for both of the variables, but that's not a real solution I think. I'd really like to use the i-named variable in most of my for-loops.
yes, the loop increment variable is in the scope of the loops parent, not inside the loop itself. This is intentional, for examples like this:
public function getPositionOfValue ( value:String ) : int
{
for ( var i:int = 0; i < someArray; i++ )
{
if (someArray[i] == value )
{
break;
}
}
return i;
}
this allows you to access the value of i once the loop is over. There are lots of cases where this is very useful.
What you should do in the cases where you have multiple loops inside the same scope is var the i outside of the loops:
public function getPositionOfValue ( value:String ) : int
{
var i:int;
for ( i = 0; i < 15; i++ )
{
//do something
}
for ( i = 0; i < 29; i++ )
{
//do something else
}
return i;
}
then you get rid of your warning. The other thing to consider is to name your loop increment variables something more descriptive.
Update: Two other things to consider:
1) you shouldn't use uints except for things like colors and places where Flex expects a uint. They are slower than int's to use. Source]1 Update: it looks like this may no longer be the case in newer versions of the flash player: source
2) when you var a loop increment variable inside of a loop declaration, you want to make sure you set it to the proper initialization value, usually 0. You can get some hard to track down bugs if you dont.
As mentioned here, as3 has global and local scope and that's about it.
It does not do block-level scoping (or for-level either). With hoisting, you can even write to variables before you define them. That's the bit that would do my head in :-)
Early versions of Visual C had this bug, leading to all sorts of wonderful funky macro workarounds but this is not a bug in as3, it's working as designed. You can either restrict your code to having the declaration in the first for only or move the declaration outside all the for statements.
Either way, it's a matter of accepting that the language works one way, even though you may think that's a bad way :-)
Declare the variable i outside the loops to avoid this. As long as you reset it (i=0) you can still use it in all loops.
var i : uint;
for (i=0; i<19; i++) SomeFunction(i);
for (i=0; i<26; i++) SomeOtherFunction(i);
Related
I've tried using hitTestObject(), but that seems to require that I make the call using a specific instance, rendering it more or less useless unless I want to have dozens of objects making dozens of collision checks each frame, which just seems wasteful and annoying to implement.
Is there any way to do collision check based on class rather than instance?
Maybe Something equivalent to this:
http://docs.yoyogames.com/source/dadiospice/002_reference/movement%20and%20collisions/collisions/place_meeting.html
Alternatively, is there any function that returns whatever a list of objects that share overlapping coordinates with the one I'm checking?
If I'm understanding your question correctly, you have several objects of that same class that each need to check for collisions against each other?
Yes, you would have to go through each object and perform a collision check against the other objects. I suppose you could write a hitTestClass function yourself, but behind the scenes it would still be the same. As far as implementing it, it's not so bad:
for( var i:int = 0; i < asteroids.length -1; ++i )
{
var a:Asteroid = asteroids[ i ];
for( var j:int = i+1; j < asteroids.length; ++j )
{
var b:Asteroid = asteroids[ j ];
var isColliding:Boolean = a.hitTestObject( b );
//Code here to do whatever in the case of collision
}
}
If computational speed becomes a concern, then there are broad-phase collision detection techniques to chunk down the time. Quad trees are one example.
If I assign a Vector like
var vec1:Vector.<Number> = new Vector.<Number>(3);
vec1 = (1,2);
the result of vec1.length is 3. Is there any built-in method to return the number of the elements actually present in the vector?
I'm an ActionScript noob so any help would be appreciated.
Well you can solve your problem by creating an empty vector instead of a defining the vector size at the time of its declaration and then you gradually add and remove elements to the vector. In this way you will always get the total number of elements inside the vector when you call vector.length
For example:
var vec1:Vector.<Number> = new Vector.<Number>();
vec1.push(5);
vec1.push(6,7);
vec1.pop();
Then vec1.length would give you 2.
Its been awhile, heres the reference: http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/Vector.html
I believe the .length is the normal way to check its length. If you want to check for "empty elements" you will need to loop through it with a loop.
I don't remmember the exact syntax, but to loop, do something like:
int count = 0;
for (int i = 0; i < vec.length; i++) {
if (vec[i] == ... );
count++;
}
I'm trying to work out a way for my game to recognise when two instances of this array have the same x or y position as another and if so to move re randomize the position of one of the instances.:
for(i=0;i<8;i++) {
PlatformInstance[i] =new Platform();
PlatformInstance[i].y= Math.random()*900;
PlatformInstance[i].x= Math.random() *1500;
stage.addChild(PlatformInstance[i]);
}
the problem i have is that the code i try detects that one platform instance has the same position as the SAME platform instance, and will constantly re randomize the position.
is there a way to differentiate between different instances?
thanks very much in advance.
EDIT
The only code i could think of was running an if statement in a loop to see whether
If (PlatformInstance[i].y == PlatformInstance[i].y)
Obviously this wouldnt work and thinking of it i know it wouldn't however i was wondering if there was a way to do:
If (Platforminstance[i].y == "other" Platforminstance[i].y
or some other words to that effect
You don't seem to have a clear understanding of how arrays work, I recommend looking into that. Something like this should work
i=0;
j=0;
while( i < PlatformInstance.length -1) {
j++;
if (j == PlatformInstance.length) {
i++;
j=i+1;
}
if( (Math.abs(PlatformInstance[i].x - PlatformInstance[j].x) < platformWidth)
|| (Math.abs(PlatformInstance[i].y - PlatformInstance[j].y) < platformHeight) ) {
PlatformInstance[j].y= Math.random()*900;
PlatformInstance[j].x= Math.random() *1500;
//Now you'll have start checking at the beginning again since you moved one
i=0;
j=0;
continue;
}
}
Also as it was previously mentioned, PlatformInstance is not a good name for an array. Only Class names should start with a capital letter. And an array of platforms should not be called an "instance". I would recommend changing it to simply platforms
I am implementing garbage collection within an AS3 app. In one part, several display objects are created within a loop like so:
for(var i:uint = 0; i <= this._exampleVector.length - 1; i++)
{
this._customText = new CustomTextObject(this._exampleVector[i].playlistText), this._customTextWidth);
this.addChild(this._customText);
etc etc
this._customTextVector.push(this._customText); // used for ref in garbage collection
}
I then perform my garbage collection preparation by looping through the _customTextVector variable.
for(var i:uint = 0; i <= this._customTextVector.length - 1; i++)
{
this.removeChild(this._customTextVector[i]);
this._customTextVector[i].gcAllObjects();
**this._customTextVector[i] = null;**
}
When I try to make the _customText within the _customTextVector null, this does not work. It only makes the index inside the Vector null. Any ideas on how to do this or another method to garbage collect?
Thanks
Chris
Is it possible to do following after looping through all the indices
_customTextVector =null;
In order to cause the AS3 Garbage Collector to GC your objects, you need to remove all references to them (including event listeners). On the next GC pass, the object's memory will be freed. There is no way to directly, instantly "null" an object like you want.
If you're having issues with memory, have a look at this post.
My code is as follows:
void Scene::copy(Scene const & source)
{
maxnum=source.maxnum;
imagelist = new Image*[maxnum];
for(int i=0; i<maxnum; i++)
{
if(source.imagelist[i] != NULL)
{
imagelist[i] = new Image;
imagelist[i]->xcoord = source.imagelist[i]->xcoord;
imagelist[i]->ycoord = source.imagelist[i]->ycoord;
(*imagelist[i])=(*source.imagelist[i]);
}
else
{
imagelist[i] = NULL;
}
}
}
A little background: The Scene class has a private int called maxnum and an dynamically allocated Array of Image pointers upon construction. These pointers point to images. The copy constructor attempts to make a deep copy of all of the images in the array. Somehow I'm getting a Segfault, but I don't see how I would be accessing an array out of bounds.
Anyone see something wrong?
I'm new to C++, so its probably something obvious.
Thanks,
I would suggest that maxnum (and maybe imagelist) become a private data member and implement const getMaxnum() and setMaxnum() methods. But I doubt that is the cause of any segfault the way you described this.
I would try removing that const before your reference and implement const public methods to extract data. It probably compiles since it is just a reference. Also, I would try switching to a pointer instead of pass by reference.
Alternatively, you can create a separate Scene class object and pass the Image type data as an array pointer. And I don't think you can declare Image *imagelist[value];.
void Scene::copy(Image *sourceimagelist, int sourcemaxnum) {
maxnum=sourcemaxnum;
imagelist=new Image[maxnum];
//...
imagelist[i].xcoord = sourceimagelist[i].xcoord;
imagelist[i].ycoord = sourceimagelist[i].ycoord;
//...
}
//...
Scene a,b;
//...
b.Copy(a.imagelist,a.maxnum);
If the source Image had maxnum set higher than the actual number of items in its imagelist, then the loop would run past the end of the source.imagelist array. Maybe maxnum is getting initialized to the value one while the array starts out empty (or maxnum might not be getting initalized at all), or maybe if you have a Scene::remove_image() function, it might have removed an imagelist entry without decrementing maxnum. I'd suggest using an std::vector rather than a raw array. The vector will keep track of its own size, so your for loop would be:
for(int i=0; i<source.imagelist.size(); i++)
and it would only access as many items as the source vector held. Another possible explanation for the crash is that one of your pointers in source.imagelist belongs to an Image that was deleted, but the pointer was never set to NULL and is now a dangling pointer.
delete source.imagelist[4];
...
... // If source.imagelist[4] wasn't set to NULL or removed from the array,
... // then we'll have trouble later.
...
for(int i=0; i<maxnum; i++)
{
if (source.imagelist[i] != NULL) // This evaluates to true even when i == 4
{
// When i == 4, we're reading the xcoord member from an Image
// object that no longer exists.
imagelist[i]->xcoord = source.imagelist[i]->xcoord;
That last line will access memory that it shouldn't. Maybe the object still happens to exist in memory because it hasn't gotten overwritten yet, or maybe it has been overwritten and you'll retrieve an invalid xcoord value. If you're lucky, though, then your program will simply crash. If you're dealing directly with new and delete, make sure that you set a pointer to NULL after you delete it so that you don't have a dangling pointer. That doesn't prevent this problem if you're holding a copy of the pointer somewhere, though, in which case the second copy isn't going to get set to NULL when you delete-and-NULL the first copy. If you later try to access the second copy of the pointer, you'll have no way of knowing that it's no longer pointing to a valid object.
It's much safer to use a smart pointer class and let that deal with memory management for you. There's a smart pointer in the standard C++ library called std::auto_ptr, but it has strange semantics and can't be used in C++ containers, such as std::vector. If you have the Boost libraries installed, though, then I'd suggest replacing your raw pointers with a boost::shared_ptr.