papervision3d相机旋转（papervision3d camera orbit）

代码如下：

package
{
	import flash.events.MouseEvent;
	
	import org.papervision3d.lights.PointLight3D;
	import org.papervision3d.materials.shadematerials.FlatShadeMaterial;
	import org.papervision3d.objects.DisplayObject3D;
	import org.papervision3d.objects.primitives.Sphere;
	import org.papervision3d.view.BasicView;
	
	[SWF(width="640", height="480", backgroundColor="#000000", frameRate="60")]
	public class OrbitingCameraExample extends BasicView
	{
		private var isOribiting:Boolean;
		private var cameraPitch:Number = 90;
		private var cameraYaw:Number = 270;
		private var cameraTarget:DisplayObject3D = DisplayObject3D.ZERO;
		private var previousMouseX:Number;
		private var previousMouseY:Number;
		
		private var light:PointLight3D;
		
		public function OrbitingCameraExample()
		{
			light = new PointLight3D();
			var material:FlatShadeMaterial = new FlatShadeMaterial(light, 0xcc0000);
			
			var sphere1:Sphere = new Sphere(material, 300, 10, 10);
			var sphere2:Sphere = new Sphere(material, 100, 10, 10);
			sphere2.x = 300;
			sphere2.y = 300;
			sphere2.z = 700
			var sphere3:Sphere = new Sphere(material, 100, 10, 10);
			sphere3.x = 600;
			sphere3.y = -400;
			sphere3.z = -200;
			var sphere4:Sphere = new Sphere(material, 100, 10, 10);
			sphere4.x = -700;
			sphere3.z = -100;
			
			scene.addChild(sphere1);
			scene.addChild(sphere2);
			scene.addChild(sphere3);
			scene.addChild(sphere4);
			
			stage.addEventListener(MouseEvent.MOUSE_DOWN, onMouseDown);
			stage.addEventListener(MouseEvent.MOUSE_MOVE, onMouseMove);
			stage.addEventListener(MouseEvent.MOUSE_UP, onMouseUp);

			startRendering();
		}

		private function onMouseDown(event:MouseEvent):void
		{
			isOribiting = true;
			previousMouseX = event.stageX;
			previousMouseY = event.stageY;
		}

		private function onMouseUp(event:MouseEvent):void
		{
			isOribiting = false;
		}
		
		private function onMouseMove(event:MouseEvent):void
		{
			var differenceX:Number = event.stageX - previousMouseX;
			var differenceY:Number = event.stageY - previousMouseY;
			
			if(isOribiting)
			{
				cameraPitch += differenceY;
				cameraYaw += differenceX;
				 
				cameraPitch %= 360;
				cameraYaw %= 360;
				
				cameraPitch = cameraPitch > 0 ? cameraPitch : 0.0001;
				cameraPitch = cameraPitch < 90 ? cameraPitch : 89.9999;
				
				previousMouseX = event.stageX;
				previousMouseY = event.stageY;
				
				camera.orbit(cameraPitch, cameraYaw, true, cameraTarget);
			}
		}
	}
}