WorldWind的渲染引擎

WorldWind中显示图像的是一个继承自Control的WorldWindow控件，代码：

public class WorldWindow : Control, IGlobe

 

初始化代码：

public WorldWindow() {     this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.Opaque, true);     // The m_Device3d can't be created unless the control is at least 1 x 1 pixels in size     this.Size = new Size(1,1);      try      {          if(!IsInDesignMode()) this.InitializeGraphics();          ......       }     catch (InvalidCallException caught)      {          throw new InvalidCallException(              "Unable to locate a compatible graphics adapter.", caught );      }     catch (NotAvailableException caught)      {          throw new NotAvailableException(              "Unable to locate a compatible graphics adapter.", caught );      } }

初始化代码中主要的是：

(1) 设置窗体的样式：

   this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.Opaque, true);

(2) 初始化DirectX，具体的关于DirectX的初始化参见《WorldWind-Direct3D的初始化》 ：

    if(!IsInDesignMode()) this.InitializeGraphics();

 

WorldWindow控件的 OnPaint() 方法：

protected override void OnPaint(PaintEventArgs e) {     try      {          if(m_Device3d==null)          {               e.Graphics.Clear(SystemColors.Control);              return;          }           Render();          m_Device3d.Present();      }     catch(DeviceLostException)      {          try          {               AttemptRecovery();               Render();                m_Device3d.Present();          }          catch(DirectXException){ }      } }

从代码中能够看出，主要的渲染操做都存在于 Render() 方法中。

 

Render()方法：

public void Render() {     try     {         this.drawArgs.BeginRender();           System.Drawing.Color backgroundColor = System.Drawing.Color.Black;          m_Device3d.Clear(ClearFlags.Target | ClearFlags.ZBuffer, backgroundColor, 1.0f, 0);          if (m_World == null)         {             m_Device3d.BeginScene();             m_Device3d.EndScene();             m_Device3d.Present();            Thread.Sleep(25);            return;         }          // 用于对图像进行逻辑处理的线程         if (m_WorkerThread == null)         {             m_WorkerThreadRunning = true;             m_WorkerThread = new Thread(new ThreadStart(WorkerThreadFunc));             m_WorkerThread.Name = "WorldWindow.WorkerThreadFunc";             m_WorkerThread.IsBackground = true;            if (World.Settings.UseBelowNormalPriorityUpdateThread)             {                 m_WorkerThread.Priority = ThreadPriority.BelowNormal;             }            else             {                 m_WorkerThread.Priority = ThreadPriority.Normal;             }             m_WorkerThread.Start();         }          m_Device3d.BeginScene();           // 渲染当前星球，这是主要的渲染过程         m_World.Render(this.drawArgs);          // 渲染位置信息         RenderPositionInfo();          // 渲染菜单栏         _menuBar.Render(drawArgs);         m_FpsGraph.Render(drawArgs);            // 渲染屏幕消息             if (m_World.OnScreenMessages != null)         {            try             {                foreach (OnScreenMessage dm in m_World.OnScreenMessages)                 {                    int xPos = (int)Math.Round(dm.X * this.Width);                    int yPos = (int)Math.Round(dm.Y * this.Height);                    Rectangle posRect = new Rectangle(xPos, yPos, this.Width, this.Height);                    this.drawArgs.defaultDrawingFont.DrawText(null,                         dm.Message, posRect,                        DrawTextFormat.NoClip | DrawTextFormat.WordBreak,                         Color.White);                 }             }            catch (Exception){}         }          m_Device3d.EndScene();     }    catch (Exception ex){ Log.Write(ex);}     finally{ this.drawArgs.EndRender();}     drawArgs.UpdateMouseCursor(this); }

 

图像逻辑处理线程方法：

private void WorkerThreadFunc() {     const int refreshIntervalMs = 150; // 更新频率：Max 6 updates per second     while(m_WorkerThreadRunning)      {          try          {               long startTicks = 0;              PerformanceTimer.QueryPerformanceCounter(ref startTicks);                 m_World.Update(this.drawArgs);                long endTicks = 0;              PerformanceTimer.QueryPerformanceCounter(ref endTicks);                float elapsedMilliSeconds = 1000*(float)(endTicks - startTicks)/PerformanceTimer.TicksPerSecond;              float remaining = refreshIntervalMs - elapsedMilliSeconds;              if(remaining > 0) Thread.Sleep((int)remaining);          }          catch(Exception caught){ Log.Write(caught);}      } }

 

WorldWind渲染循环：

/// <summary> /// The world render loop. Borrowed from FlightGear and Tom Miller's blog /// </summary> public void OnApplicationIdle(object sender, EventArgs e) {     // Sleep will always overshoot by a bit so under-sleep by 2ms in the hopes of never oversleeping.     const float SleepOverHeadSeconds = 2e-3f;     // Overhead associated with displaying the frame     const float PresentOverheadSeconds = 0;//3e-4f;     try      {          if (Parent.Focused && !Focused) Focus();           while (IsAppStillIdle)          {                Render();               if (World.Settings.ThrottleFpsHz > 0)               {                   // optionally throttle the frame rate (to get consistent frame rates or reduce CPU usage.                   float frameSeconds = 1.0f / World.Settings.ThrottleFpsHz - PresentOverheadSeconds;                   // Sleep for remaining period of time until next render                   float sleepSeconds = frameSeconds - SleepOverHeadSeconds - DrawArgs.SecondsSinceLastFrame;                   if(sleepSeconds > 0)                    {                       // Don't sleep too long. We don't know the accuracy of Thread.Sleep                       Thread.Sleep((int) (1000 * sleepSeconds));                       // Burn off what little time still remains at 100% CPU load                       while(DrawArgs.SecondsSinceLastFrame < frameSeconds)                        {                            // Patience                        }                    }               }               drawArgs.Present();          }      }     catch(DeviceLostException){ AttemptRecovery();}     catch(Exception caught){ Log.Write(caught);} }

 

IsAppStillIdle属性 

/// <summary> /// Determine whether any window messages is queued. /// </summary> private static bool IsAppStillIdle {     get      {          NativeMethods.Message msg;          return !NativeMethods.PeekMessage(out msg, IntPtr.Zero, 0, 0, 0);      } }

 

 

WorldWind的渲染循环是在 Application Idle 时进行的：

Application.ThreadException += new ThreadExceptionEventHandler(Application_ThreadException); MainApplication app = new MainApplication(); Application.Idle += new EventHandler(app.WorldWindow.OnApplicationIdle); Application.Run(app);