ActionScript: The Definitive Guide

Movie and Instance Stacking Order

All movie clip instances and externally loaded movies displayed in the Player reside in a visual stacking order akin to a deck of cards. When instances or externally loaded .swf files overlap in the Player, one clip (the “higher” of the two) always covers up the other clip (the “lower” of the two). Simple enough in principle, but the main stack, which contains all the instances and .swf files, is actually divided into many smaller substacks. We’ll look at these substacks individually first, then see how they combine to form the main stack. (The stack in this discussion has no direct relation to the LIFO and FIFO stacks discussed in Chapter 11.)

The Internal Layer Stack

Instances created manually in the Flash authoring tool reside in a stack called the internal layer stack. This stack’s order is governed by the actual layers in a movie’s timeline; when two manually created instances on separate timeline layers overlap, the instance on the uppermost layer obscures the instance on the lowermost layer.

Furthermore, because multiple clips may reside on a single timeline layer, each layer in the internal layer stack actually maintains its own ministack. Overlapping clips that reside on the same layer of a timeline are stacked in the authoring tool via the Modify → Arrange commands.

As of Flash 5, we can swap the position of two instances in the internal layer stack using the swapDepths( ) method, provided they reside on the same timeline (that is, ...