ActionScript 3.0 Design Patterns

222 | Chapter 6: Composite Pattern

playlist called “eclectic” that includes both previous playlists and an additional song.

The following text output shows the song play sequence.

Queuing playlist: eclectic

Queuing playlist: drum licks

Queuing playlist: guitar riffs

playing bongo

playing tabla

playing djembe

playing ballad piano

playing acoustic guitar

playing electric guitar

When the “eclectic” playlist is queued for play, it queues and plays the embedded

“drum licks” and “guitar riffs” playlists as well. This is exactly the behavior we

expect from our composite playlist structure. You can easily remove songs and

playlists by implementing theremove( ) method as shown in the minimalist example.

Example: Animating Composite Objects Using Inverse Kinematics

There are many examples of excellent Flash games that use ActionScript to animate

characters on stage. Even a simple animated figure can have independently function-

ing body parts such as arms and legs that can be animated to jump, run, and kick.

Can we develop comple xanimated figures by treating body parts as composite and

component objects? Do we gain an advantage by being able to treat component and

composite parts of an animated figure in the same way? Indeed, the composite pat-

tern brings several advantages to animation, as will be evident by the animated snake

that will be developed in this example. Figure 6-6 shows a screenshot of the snake

that moves by means of inverse kinematics.

Figure 6-6. Snake constructed using a composite pattern