|
Movie clips
are a key element for people who create animated content with the Flash
authoring tool and want to control that content with ActionScript. Whenever
you create a movie clip symbol in Flash, Flash adds the symbol to
the library of that Flash document. By default, this symbol becomes
an instance of the
MovieClip class
, and as such has the
properties and methods of the MovieClip class.
When an instance of a movie clip symbol is placed on the Stage,
the movie clip automatically progresses through its timeline (if
it has more than one frame) unless its playback is altered using
ActionScript. It is this timeline that distinguishes the MovieClip
class, allowing you to create animation through motion or shape
tweens through the Flash authoring tool. By contrast, with a display
object that is an instance of the Sprite class, you can create animation
only by programmatically changing the object’s values.
In previous versions of ActionScript, the MovieClip class was
the base class of all instances on the Stage. In ActionScript 3.0,
a movie clip is only one of many display objects that can appear
on the screen. If a timeline is not necessary for the function of
a display object, using the Shape class or Sprite class in lieu
of the MovieClip class may improve rendering performance. For more
information on choosing the appropriate display object for a task,
see
Choosing a DisplayObject subclass
.
Important concepts and terms
The following
reference list contains important terms related to movie clips:
-
AVM1 SWF
-
A SWF file created using ActionScript 1.0 or ActionScript
2.0, usually targeting Flash Player 8 or earlier.
-
AVM2 SWF
-
A SWF file created using ActionScript 3.0 for Adobe Flash
Player 9 or later or Adobe AIR.
-
External SWF
-
A SWF file that is created separately from the project SWF
file and is intended to be loaded into the project SWF file and
played back within that SWF file.
-
Frame
-
The smallest division of time on the timeline. As with a
motion picture filmstrip, each frame is like a snapshot of the animation
in time, and when frames are played quickly in sequence, the effect
of animation is created.
-
Timeline
-
The metaphorical representation of the series of frames that
make up a movie clip’s animation sequence. The timeline of a MovieClip
object is equivalent to the timeline in the Flash authoring tool.
-
Playhead
-
A marker identifying the location (frame) in the timeline
that is being displayed at a given moment.
|
|
|
