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PerspectiveProjection

Package | flash.geom
Class | public class PerspectiveProjection
Inheritance | PerspectiveProjection Object

Language Version : | ActionScript 3.0

Player Version : | Flash Player 10

The PerspectiveProjection class provides an easy way to assign or modify the perspective transformations of a display object and all of its children. For more complex or custom perspective transformations, use the Matrix3D class. While the PerspectiveProjection class provides basic three-dimensional presentation properties, the Matrix3D class provides more detailed control over the three-dimensional presentation of display objects.

Projection is a way of representing a three-dimensional object in a two-dimensional space, like a cube projected onto a computer screen. Perspective projection uses a viewing frustum (a rectangular pyramid) to model and project a three-dimensional world and its objects on the screen. The viewing frustum becomes increasingly wider as it moves further from the origin of the viewpoint. The origin of the viewpoint could be a camera or the eyes of an observer facing the screen. The projected perspective produces the illusion of three dimensions with depth and distance, where the objects closer to the screen appear larger than the objects farther from the screen.

A default PerspectiveProjection object is a framework defined for perspective transformation of the root object, based on the field of view and aspect ratio (dimensions) of the stage. The projection center, the vanishing point, is set to the center of the stage, which means the three-dimensional display objects disappear toward the center of the stage as they move back in the z-axis. The default viewpoint is at point (0,0) looking down the positive z-axis. The y-axis points down toward the bottom of the screen. You can gain access to the `root` display object's perspective projection settings, and change the field of view and projection center properties of the `perspectiveProjection` property, through the `root` object's `DisplayObject.transform` property.

You can also set a different perspective projection setting for a display object through the parent's perspective projection. First, create a PerspectiveProjection object and set its `fieldOfView` and `projectionCenter` properties. Next, assign the PerspectiveProjection object to the parent display object using the `DisplayObject.transform` property. The specified projection matrix and transformation will then apply to all the display object's three-dimensional children.

See also

flash.display.DisplayObject.transform
flash.geom.Transform
flash.geom.Matrix3D
flash.geom.Utils3D

Public Properties
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| Property | Defined By
--- | --- | ---
|  | constructor : Object A reference to the class object or constructor function for a given object instance. | Object
|  | fieldOfView : Number Specifies an angle, as a degree between 0 and 180, for the field of view in three dimensions. | PerspectiveProjection
|  | focalLength : Number [read-only] The distance between the eye or the viewpoint's origin (0,0,0) and the display object located in the z-axis. | PerspectiveProjection
|  | projectionCenter : Point A two-dimensional point representing the center of the projection, the vanishing point for the display object. | PerspectiveProjection
|  | prototype : Object [static] A reference to the prototype object of a class or function object. | Object

Public Methods
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| Method | Defined By
--- | --- | ---
|  | PerspectiveProjection() Creates an instance of a PerspectiveProjection object. | PerspectiveProjection
|  | hasOwnProperty(name:String):Boolean Indicates whether an object has a specified property defined. | Object
|  | isPrototypeOf(theClass:Object):Boolean Indicates whether an instance of the Object class is in the prototype chain of the object specified as the parameter. | Object
|  | propertyIsEnumerable(name:String):Boolean Indicates whether the specified property exists and is enumerable. | Object
|  | setPropertyIsEnumerable(name:String, isEnum:Boolean = true):void Sets the availability of a dynamic property for loop operations. | Object
|  | toMatrix3D():Matrix3D Returns The underlying Matrix3D object of the display object. | PerspectiveProjection
|  | toString():String Returns the string representation of the specified object. | Object
|  | valueOf():Object Returns the primitive value of the specified object. | Object

Property Detail

fieldOfView | property

`fieldOfView:Number` [read-write]

Language Version : | ActionScript 3.0

Player Version : | Flash Player 10

Specifies an angle, as a degree between `0` and `180`, for the field of view in three dimensions. This value determines how strong the perspective transformation and distortion applies to a three-dimensional display object with a non-zero z-coordinate.

A degree close to `0` means that the screen's two-dimensional x- and y-coordinates are roughly the same as the three-dimensional x-, y-, and z-coordinates with little or no distortion. In other words, for a small angle, a display object moving down the z-axis appears to stay near the same size and moves little.

A value close to `180` degrees results in a fisheye lens effect: positions with a `z` value smaller than `0` are magnified, while positions with a `z` value larger than `0` are minimized. With a large angle, a display object moving down the z-axis appears to change size quickly and moves a great distance. If the field of view is set to `0` or `180`, nothing is seen on the screen.

Implementation
`public function get fieldOfView():Number`
`public function set fieldOfView(value:Number):void`

focalLength | property |

`focalLength:Number` [read-only]

Language Version : | ActionScript 3.0

Player Version : | Flash Player 10

The distance between the eye or the viewpoint's origin (0,0,0) and the display object located in the z-axis. During the perspective transformation, the `focalLength` is calculated dynamically using the angle of the field of view and the stage's aspect ratio (stage width divided by stage height).

Implementation
`public function get focalLength():Number`

See also

fieldOfView

projectionCenter | property |

`projectionCenter:Point` [read-write]

Language Version : | ActionScript 3.0

Player Version : | Flash Player 10

A two-dimensional point representing the center of the projection, the vanishing point for the display object.

The `projectionCenter` property is an offset to the default registration point that is the upper left of the stage, point (0,0). The default projection transformation center is in the middle of the stage, which means the three-dimensional display objects disappear toward the center of the stage as they move backwards in the z-axis.

Implementation
`public function get projectionCenter():Point`
`public function set projectionCenter(value:Point):void`
Constructor Detail

PerspectiveProjection | () | Constructor

`public function PerspectiveProjection()`

Language Version : | ActionScript 3.0

Player Version : | Flash Player 10

Creates an instance of a PerspectiveProjection object.

Method Detail

toMatrix3D | () | method

`public function toMatrix3D():Matrix3D`

Language Version : | ActionScript 3.0

Player Version : | Flash Player 10

Returns The underlying Matrix3D object of the display object.

A display object, like the root object, can have a PerspectiveProjection object without needing a Matrix3D property defined for its transformations. In fact, use either a PerspectiveProjection or a Matrix3D object to specify the perspective transformation. If when using the PerspectiveProjection object, a Matrix3D object was needed, the `toMatrix3D()` method can retrieve the underlying Matrix3D object of the display object. For example, the `toMatrix3D()` method can be used with the `Utils3D.projectVectors()` method.

Returns

| `Matrix3D` — The underlying Matrix3D object.

See also

flash.geom.Matrix3D

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Tue May 20 2008, 04:02 AM -07:00