Perl Graphics Programming

The SWF::DisplayItem Module

Each object that is on-screen at any particular time has an entry in a data structure in the SWF player called the display list. The display list keeps track of the position of the object, the depth of the object, and a transformation matrix that affects how the object is drawn on the screen. The SWF::DisplayItem object defines methods for moving, transforming, and arranging objects in the display list. The following attributes are contained in a DisplayItem:

Name

A label used to refer to the item in ActionScript scripts

Position

The x, y coordinate of the item within a frame

Scale

A horizontal and vertical scale multiplier

Rotation

An angular offset

Skew

A horizontal and vertical skew offset

Depth

The position of the item in the display list

Ratio

If the displayed item is a Morph object, the ratio attribute determines which frame of the morph transition is displayed

Color transform

The object’s red, green, blue, and alpha components may have a color offset applied to them

DisplayItems do not have their own constructors. New DisplayItems are created when a displayable object is added to a movie or a sprite; the add( ) method of these objects returns an SWF::DisplayItem object.

In the example at the beginning of this chapter, we moved the various items around the Stage using an ActionScript event loop. Example 9-1 creates a 60-frame animation where each shape is manually placed within the frame by maintaining a list of DisplayItems for each object on the Stage.

Example 9-1. Using ...