Comments on: Understanding Flash’s Coordinate Systems

By: Michael Williams

Michael Williams — Wed, 21 Oct 2009 16:29:19 +0000

If you're looking for a more practical application of all this, check out my new tutorial on parallax scrolling.

By: Michael Williams

Michael Williams — Fri, 09 Oct 2009 15:48:31 +0000

Thank you Free Games Haha, yes the same thing happens with me, I often find posts just after I need them

By: Free Games

Free Games — Wed, 07 Oct 2009 18:03:50 +0000

Awesome post, thanks for all the detail. I've been struggling with learning actionscript and its websites like yours that keep allowing me to make slow and steady progress. Of course, I usually find websites like yours after I have beaten my head bloody against the wall trying to figure out some of these quirks! Thanks again!

.-= Free Games´s last blog: Square Jump =-.

By: Michael Williams

Michael Williams — Thu, 20 Aug 2009 11:16:22 +0000

Thanks, Porter!

By: Porter

Porter — Thu, 20 Aug 2009 01:07:32 +0000

That's definitely the most in depth explanation I've ever seen. If ever I need to explain this to someone, this is definitely where I'll send them, great work.

.-= Porter´s last blog: Do Sponsors Care About More Than CTR? =-.

By: arxanas

arxanas — Sat, 15 Aug 2009 01:29:52 +0000

Okay then, that’s what I needed to know. Thanks!

By: Michael Williams

Michael Williams — Fri, 14 Aug 2009 23:41:01 +0000

The lowest object in a container has an index of 0, and none can be negative.

All the DisplayObjects within a DisplayObjectContainer have an index from 0 to ( number of display objects - 1 ). If one of those DisplayObjects happens to be a DisplayObjectContainer itself, and contain even more DisplayObjects, then each of those DisplayObjects has an index from 0 to ( number of display objects in the inner DisplayObjectContainer - 1 ). And so on.

It's called a "composite pattern"; it's self-similar, like a fractal. Hard to explain in text, haha!

By: arxanas

arxanas — Fri, 14 Aug 2009 13:15:01 +0000

Ah, very useful. I remember someone at FrozenHaddock's forum asked how to keep stuff on top (namely, a mute button). This would have been rather useful to whomever that was. Can indexes (indices, whatever) also go negative? Or is it all above zero?

And do these containers exist on certain indexes, which then have some sort of virtual "sub-indexes"?

By: Michael Williams

Michael Williams — Thu, 13 Aug 2009 16:09:52 +0000

Sure -- actually there are several ways. As I understand it, AS2 gave every object a "depth index", right? AS3 does a similar thing, but with one big exception: there are no gaps. So, you can't have an object with index 4 and then insert the next one at index 1000. Also, if you have objects at index 0, 1, and 2 (say), then insert another item at index 1, the objects currently at index 1 and 2 will move to indices 3 and 4.

The relevant functions are:

container.getChildIndex( child:DisplayObject ):int -- gets the depth index of the child object within container.

container.setChildIndex( child:DisplayObject, index:int ) -- sets the depth index of the child object within container.

container.addChildAt( child:DisplayObject, index:int ) -- like addChild() except inserts the new object at the specified index within container.

container.getChildAt( index:int ):DisplayObject -- gets the object within container at the given index.

container.swapChildren( child1:DisplayObject, child2:DisplayObject ) -- swaps the indices of the two objects specified (must be within container)

container.swapChildrenAt( index1:int, index2:int ) -- swaps the indices of the two objects that are at the given indices.

And of course you can combine these, like writing container.addChildAt( newBullet, getChildIndex( gun ) - 1 ) to add the new bullet underneath the gun.

Personally I really like using the method you suggested, separating objects into different containers. This is particularly useful for making a HUD that doesn't scroll and a background that scrolls at a different rate to the main sprites.

By: arxanas

arxanas — Thu, 13 Aug 2009 03:15:14 +0000

Is there a way to rearrange the order of these containers? For example, in my game, I’m firing bullets, but they appear on top of the gun and start moving, as opposed to under, so it seems as though it’s actually leaving the gun. I know AS2 had depth control, but does AS3 have any such thing?

Although the logical solution is probably to create a container for the bullets (and organize every type of object in the game) beneath the gun…