ActionScript for Flash MX: The Definitive Guide, Second Edition

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Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 13: Movie Clips

same position on screen, the one with the greater depth value is rendered in front of

the other.

Although multiple clips can occupy a single author-time timeline layer, all depth

positions are single-occupant dwellings. Only one clip can occupy a depth position

at a time—placing a clip into an occupied position displaces (and deletes) the layer’s

previous occupant.

It’s okay for there to be gaps in the depths of clips; you can have a clip at depth 0,

another at depth 500, and a third one at depth 1000. No performance hit or increase

in memory consumption results from having gaps in your depth assignments.

The .swf Document “_level” Stack

In addition to the internal layer stack and the programmatically generated content

stack, there’s a third (and final) kind of stack, the document stack (or level stack),

which governs the overlapping not of instances, but of entire .swf files loaded into

the Player via loadMovie().

The first .swf file loaded into the Flash Player is placed in the lowest level of the doc-

ument stack (represented by the global property

_level0). If we load any additional

.swf files into the Player after that first document, we can optionally place them in

front of the original document by assigning them to a level above

_level0 in the doc-

ument ...