Stacking Order (swapDepth)
      by kirupa

A common misconception is that the vertical "stacking" order of objects in Flash is determined by which layer the object is in. The objects in the bottom layer will always be below an object near a higher layer. If you are one of those who believes in that myth, your whole perception of what is real and what is imaginary is going to change. It is possible to adjust the stacking order of objects in Flash.

"We hold these truths to be self evident that the stacking order of objects can be changed by following Kirupa's tutorial".

If you are not big on classic American historical quotes, the following example might help:


[ click and drag any of the windows; notice how the selected window goes on top ]

While I could tell you to create the interface from scratch like some of those "other" sites, I am going to be kind enough to provide an incomplete FLA for you to download.

Partial Incomplete Source

Here is how to change the stacking order:

  1. Make sure you open the file swapwindow.fla that you downloaded from the previous link. The file only contains the actions for causing the window to be dragged; you will add the swapDepth function yourself.
  2. You should see three colored windows once you open the animation. The windows are nothing spectacular; the windows are in a button stored inside a movie clip. I will explain how to the window was created near the end of the tutorial.
  3. Right click on the green window movie clip and select "Edit In Place". You are now at the window's button state. Right click on the green window and select Actions. Copy and paste the following code below the other actions found in the Object Actions window.

[ copy and paste the above code in the Object Actions window ]

  1. You will not need to add the actions to the other windows. The code is very similar, and forcing you to add the similar code is quite redundant. Preview the animation and see that when the green window is dragged or clicked, it gets focus (it goes above all other windows).

Partial Source
Because you downloaded the interface and partial source, I will explain briefly how the interface was created.

  1. I first created the window by drawing two rectangles and adding a border.

[ the window drawn in Flash ]

  1. I then selected the entire window and pressed F8 (Insert | Convert to Symbol). From the Symbol Properties dialog box, I selected Button and pressed OK. The window is now a button.
  2. Select the window (which is now a button). Press F8 again. From the Symbol Properties dialog box, select Movie Clip. Press OK to close the Symbol Properties dialog box.

That is all there is to creating the window movie clip. Why did I convert the symbol to a button then a movie clip? As you now, the window changed its vertical order when you clicked on the object. Only buttons support mouse actions. The swapDepth function, just like all Flash functions, works only when targeted to a movie clip.

Therefore, I needed to place the button (to support mouse actions) inside a movie clip (to support Flash 5 Actions). That is why when you added the Actions, you first had to right click on the green window and select Edit In Place. You entered inside the movie clip instance to see the button form of the green window.

The final step is to give the movie clip a name. I gave each window a name depending on its color. For example, the green window is coincidentally called green! Remember that instance names can only be given to movie clips, that is why you have to go to the main timeline and then select the movie clip instance of the green window to give it an instance name.

How Does the Code Work?
The following section will basically deconstruct how the code causes the stacking order of the windows to be modified.

on (press, release, dragOver, dragOut) {
     _root.x +=2;;

The first line is the On handler for the button. The code following this statement will be enabled and executed when the mouse either presses, releases, drags over, or drags out over the window. You can access these options by going to Basic Actions | On Mouse Event from the Object Actions window.

on (press, release, dragOver, dragOut) {
     _root.x +=2;;

This is a counter for the variable x. The variable x is stored on the main timeline, _root. Why? The value of x will constantly be updated as you click on each panel. The +=2 is an incremental operator that increases the value of x by 2.

If x were simply declared as x +=2, the value of x is localized only to this movie clip. If I want another panel to increase its stacking order in relation to this panel, I can blindly increase the stacking position of that panel, or, I can increase a variable stored on the main timeline by a certain value so all movie clips are in sync.

on (press, release, dragOver, dragOut) {
     _root.x +=2;;

The line in blue is the most important line contained in this block of code. It includes the swapDepth function that enables a movie clip to change its stacking order. Because I am referring to a movie clip stored on the main timeline, I need to tell Flash to retrace my steps to reach the movie clip.

_root tells Flash to start at the main timeline to find the movie clip. The word green is the instance name of the movie clip. Basically, I am telling Flash to go to the very beginning and target the movie clip green. The swapDepths (_root.x); line tells Flash to adjust the stacking order of the movie to whatever variable x currently is.

The higher the stacking number, the higher up the window movie clip will be placed. The stacking order is relational to other objects in a surrounding area.

Never to leave you surprised or confused, I have provided the final source file for this tutorial. If you still have questions, you can post them in the forum by clicking the Message Board link below.

Final Source for this Tutorial

While this effect is cool and such, what practical uses are there for this feature? Plenty! Many sites have content that loads up in tiny modular windows. You can modify the stacking order and display the content that has currently be clicked on.

A great example of this feature can be found on the following site:

Just a final word before we wrap up. If you have a question and/or want to be part of a friendly, collaborative community of over 220k other developers like yourself, post on the forums for a quick response!

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