Screen Updates

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In some cases, code execution can delay screen updates for many seconds, up to a
maximum determined by the max-execution-time compiler option, which is set to 15
seconds by default. Any script that does not complete within the amount of time specified
by max-execution-time generates a ScriptTimeoutError exception.

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Flash Player’s frame rate can be set in one of three ways:
• Using the mxmlc compiler argument default-frame-rate
• Using the Document Properties dialog in the Flash authoring tool
• Using the Stage class’s instance variable frameRate within a running .swf file

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Even though the Flash runtime performs scheduled screen updates according to the
frame rate, the number of screen updates that can actually be achieved per second
(the actual frame rate) is often less than the frame rate specified by the programmer
(the designated frame rate). The actual frame rate varies greatly depending on factors
such as the speed of the computer, available system resources, the physical refresh
rate of the display device, and the complexity of the content running in the Flash
runtime.

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ActionScript gives every mouse and keyboard event listener function the special ability
to trigger a post-event screen update. A post-event screen update is an update that
occurs immediately following the dispatch of an event, ahead of the next scheduled
update.

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To allow the screen to be updated immediately following the passage of some arbitrary
amount of time, ActionScript provides the TimerEvent.updateAfterEvent( )
method, which forces a post-event screen update after a TimerEvent.TIMER event.
The TimerEvent.updateAfterEvent( ) method is used within TimerEvent.TIMER event
listener functions, in exactly the same way that MouseEvent.updateAfterEvent( ) and
KeyboardEvent.updateAfterEvent( ) are used within mouse and keyboard event listener
functions.

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More specifically, when the Flash runtime updates the screen, it
renders only those areas that have changed since the last update.

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The Event.RENDER event is a specialized type of screen-update event used in advanced
situations where graphics performance is critical. Its primary purpose is to let the
programmer defer the execution of all custom drawing routines until the precise
moment before the screen is rendered, thus eliminating duplicate drawing-routine
execution.

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Unlike all other built-in Flash runtime events, the Event.RENDER event
must be requested manually by the programmer

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The Flash runtime dispatches the
Event.RENDER event when the following two conditions are both true:
• The Flash runtime is about to check if the screen needs updating (whether due
to a frame passing or an updateAfterEvent( ) call).
• The programmer has invoked stage.invalidate( ).

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The StageDetector.ADDED_TO_STAGE event is dispatched when an object is added to
the display list, at which point the Ellipse class will register renderListener( ) for the
Event.RENDER event. The StageDetector.REMOVED_FROM_STAGE event is dispatched when
an object is removed from the display list