[WorldWind学习]4.DrawArgs对象

 WorldWind的WorldWindow控件包含只读属性DrawArgs

public DrawArgs DrawArgs
        {
            get { return this.drawArgs; }
        }

DrawArgs渲染参数对象，负责记录当前渲染的各个参数

WorldWindow的CurrentWorld属性赋值时也给drawArgs的CurrentWorld赋值。

public World CurrentWorld
        {
            get
            {
                return m_World;
            }
            set
            {
                m_World = value;
                if(m_World != null)
                {
                    MomentumCamera camera = new MomentumCamera(m_World.Position, m_World.EquatorialRadius );
                    if(!World.Settings.CameraResetsAtStartup)
                    {
                        camera.SetPosition(
                            World.Settings.CameraLatitude.Degrees,
                            World.Settings.CameraLongitude.Degrees,
                            World.Settings.CameraHeading.Degrees, 
                            World.Settings.CameraAltitude,
                            World.Settings.CameraTilt.Degrees,
                            0
                            );
                    }
                    this.drawArgs.WorldCamera = camera;
                    
                    this.drawArgs.CurrentWorld = value;
                    this.layerManagerButton = new LayerManagerButton(
                        Path.Combine(Path.GetDirectoryName(Application.ExecutablePath), @"Data\Icons\Interface\layer-manager2.png"),
                        m_World);
                    
                    this._menuBar.AddToolsMenuButton( this.layerManagerButton, 0 );
                    this._menuBar.AddToolsMenuButton( new PositionMenuButton( Path.GetDirectoryName(Application.ExecutablePath) + "\\Data\\Icons\\Interface\\coordinates.png"), 1);
                    this._menuBar.AddToolsMenuButton( new LatLonMenuButton( Path.GetDirectoryName(Application.ExecutablePath) + "\\Data\\Icons\\Interface\\lat-long.png", m_World), 2);
                    this.layerManagerButton.SetPushed(World.Settings.ShowLayerManager);
                    
                    // TODO: Decide how to load grids
                    m_World.RenderableObjects.Add(new Renderable.LatLongGrid(m_World));
                }
            }
        }

drawArgs的WorldCamera属性，注意DrawArgs类的public static CameraBase Camera = null;Camera是一个静态对象，具有缓存相机的作用。