通过围绕要旋转的对象中心的注册点旋转。
Yahoo Astra有一个动态注册类来处理这样的事情。
这可以实现为：
package
{
import com.yahoo.astra.utils.DynamicRegistration;
import flash.display.MovieClip;
import flash.events.Event;
import flash.geom.Point;
public class Bullet extends MovieClip
{
private var mc:MovieClip;
private var currentRotation:uint = 0;
public function Bullet()
{
mc = new MovieClip();
mc.graphics.beginFill(0);
mc.graphics.drawRect(120, 120, 40, 40);
mc.graphics.endFill();
addChild(mc);
addEventListener(Event.ENTER_FRAME, onEnterFrame);
}
private function onEnterFrame(e:Event):void
{
currentRotation = (currentRotation + 10) % 360;
DynamicRegistration.rotate(mc, new Point(140, 140), currentRotation);
}
}
}
Yahoo Astra DynamicRegistration 类：
/*
Copyright (c) 2008 Yahoo! Inc. All rights reserved.
The copyrights embodied in the content of this file are licensed under the BSD (revised) open source license
*/
package com.yahoo.astra.utils
{
import flash.geom.Point;
import flash.display.DisplayObject;
/**
* Allows you to manipulate display objects based on a registration point other
* than the standard (0,0).
*
* @author Josh Tynjala
*/
public class DynamicRegistration
{
/**
* Moves a <code>DisplayObject</code> to a new position (x,y) based on a registration point. The
* true position of the object will be (x - registration.x, y - registration.y).
*
* @param target the DisplayObject to move
* @param registration the registration point of the DisplayObject
* @param x the new x position, in pixels
* @param y the new y position, in pixels
*/
public static function move(target:DisplayObject, registration:Point, x:Number = 0, y:Number = 0):void
{
//generate the location of the registration point in the parent
registration = target.localToGlobal(registration);
registration = target.parent.globalToLocal(registration);
//move the target and offset by the registration point
target.x += x - registration.x;
target.y += y - registration.y;
}
/**
* Rotates a <code>DisplayObject</code> based on a registration point.
*
* @param target the DisplayObject to move
* @param registration the registration point of the DisplayObject
* @param rotation the new rotation angle
*/
public static function rotate(target:DisplayObject, registration:Point, degrees:Number = 0):void
{
changePropertyOnRegistrationPoint(target, registration, "rotation", degrees);
}
/**
* Scales a <code>DisplayObject</code> based on a registration point.
*
* @param target the DisplayObject to move
* @param registration the registration point of the DisplayObject
* @param scaleX the new x scaling factor
* @param scaleY the new y scaling factor
*/
public static function scale(target:DisplayObject, registration:Point, scaleX:Number = 0, scaleY:Number = 0):void
{
changePropertyOnRegistrationPoint(target, registration, "scaleX", scaleX);
changePropertyOnRegistrationPoint(target, registration, "scaleY", scaleY);
}
/**
* @private
* Alters an arbitary property based on the registration point.
*
* @param target the DisplayObject to move
* @param registration the registration point of the DisplayObject
* @param propertyName the property to change
* @param value the new value of the property to change
*/
private static function changePropertyOnRegistrationPoint(target:DisplayObject, registration:Point, propertyName:String, value:Number):void
{
//generate the location of the registration point in the parent
var a:Point = registration.clone();
a = target.localToGlobal(a);
a = target.parent.globalToLocal(a);
target[propertyName] = value;
//after the property change, regenerate the location of the registration
//point in the parent
var b:Point = registration.clone();
b = target.localToGlobal(b);
b = target.parent.globalToLocal(b);
//move the target based on the difference to make it appear the change
//happened based on the registration point
target.x -= b.x - a.x;
target.y -= b.y - a.y;
}
}
}