WorldWind学习系列六：渲染过程解析篇

原文转自：http://www.cnblogs.com/wuhenke/archive/2009/12/14/1624122.html

今天主要是分析学习了Render问题，搞明白了WorldWind中整个Render绘制处理过程。其中关键类是：RenderableObject.cs ,RenderobjectList.cs.
　　WW中所有需要绘制的对象都RenderableObject，WW的各功能的执行显示都是不断地调用相应的Render方法。
        1.RenderableObject整个绘制对象继承图

WW绘制都是通过RenderableObject类，将所有的要绘制对象都看做是RenderableObject，从而统一了整个系统WW的绘制对象的绘制过程。
　　2.RenderableObjectList也继承自RenderableObject，先看看它的继承图

摘录内容：

　　“实际的点线，平面纹理等渲染对象都是从RenderableObject继承，最终的渲染实现也是在从它继续下来的类中，RenderableObjectList的成员m_children（protected ArrayList m_children = new ArrayList();）包含WW中所有的渲染对象，绘制过程中按如下的优先级进行：

public enum RenderPriority

     {

         SurfaceImages = 0,

         TerrainMappedImages = 100,

         AtmosphericImages = 200,

         LinePaths = 300,

         Icons = 400,

         Placenames = 500,

         Custom = 600

     }

这里对WW调试过程中的m_children的成员做个截图，需要注意的是m_children的成员大部分还是RenderableObjectList对象，向下包含的层次很多，但只有最底层的从RenderableObject继续的对象才是渲染的最终实现。”摘自：http://blog.sina.com.cn/s/blog_467b6cd601008mmd.html~type=v5_one&label=rela_nextarticle
　　RenderableObjectList可以简单看作RenderableObject对象的集合，但实质上存储RenderableObject对象集合的仅仅是其中的属性m_children，它有很多特有的针对m_children管理的方法，如：Add(RenderableObject ro)、Remove(RenderableObject layer)。RenderableObjectList里通过该Timer.Elapsed 事件实现了自动刷新渲染的功能。这里还有个知识点，我们可以学习一下，就是Timer.Elapsed 事件使用,请参考MS的http://msdn.microsoft.com/zh-cn/library/system.timers.timer.elapsed(VS.80).aspx。
 3.下面让我们一起看看WW实现渲染绘制的整个代码调用流程，主要分为两部分：一、获取到所有的要绘制对象集合，二、绘制所有要绘制的对象。分析入口还是从WorldWind.cs的MainAppliaction()方法开始的。
 
        3.1获取到所有的要绘制对象集合，存放到World.cs中的 RenderableObjects属性里
MainAppliaction()中调用OpenStartupWorld()
——》2974行OpenWorld( curWorldFile );调用了private void OpenWorld(string worldXmlFile)方法
——》3049行 worldWindow.CurrentWorld = WorldWind.ConfigurationLoader.Load(worldXmlFile, worldWindow.Cache);调用了CongfigurationLoader.cs的public static World Load(string filename, Cache cache)方法

 

——》CongfigurationLoader.cs 的110行 newWorld.RenderableObjects = getRenderablesFromLayerDirectory(layerDirectory, newWorld, cache); 看代码

加载渲染对象代码 


Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->        public static World Load(string filename, Cache cache)
        {
            Log.Write(Log.Levels.Debug, "CONF", "Loading " + filename);

            // get the World Wind Settings through reflection to avoid changing the signature of Load().
            Assembly a = Assembly.GetEntryAssembly();
            Type appType = a.GetType("WorldWind.MainApplication");
            System.Reflection.FieldInfo finfo = appType.GetField("Settings", BindingFlags.Static | BindingFlags.Public | BindingFlags.GetField);
            WorldWindSettings settings = finfo.GetValue(null) as WorldWindSettings;

            XmlReaderSettings readerSettings = new XmlReaderSettings();

            if (settings.ValidateXML)
            {
                Log.Write(Log.Levels.Debug, "CONF", "validating " + filename + " against WorldXmlDescriptor.xsd and LayerSet.xsd");
                readerSettings.ValidationType = ValidationType.Schema;
                /* load the schema to validate against instead of hoping for an inline schema reference */
                XmlSchemaSet schemas = new XmlSchemaSet();
                schemas.Add(null, settings.ConfigPath + "/WorldXmlDescriptor.xsd");
                schemas.Add(null, settings.ConfigPath + "/Earth/LayerSet.xsd");


                readerSettings.Schemas = schemas;
                readerSettings.ValidationEventHandler += new ValidationEventHandler(XMLValidationCallback);
                readerSettings.ValidationFlags |= System.Xml.Schema.XmlSchemaValidationFlags.ReportValidationWarnings;
            }
            else
            {
                Log.Write(Log.Levels.Debug, "CONF", "loading " + filename + " without validation");
                readerSettings.ValidationType = ValidationType.None;
            }

            try
            {
                XmlReader docReader = XmlReader.Create(filename, readerSettings);
                XPathDocument docNav = new XPathDocument(docReader);
                XPathNavigator nav = docNav.CreateNavigator();

                XPathNodeIterator worldIter = nav.Select("/World[@Name]");
                if (worldIter.Count > 0)
                {
                    worldIter.MoveNext();
                    string worldName = worldIter.Current.GetAttribute("Name", "");
                    double equatorialRadius = ParseDouble(worldIter.Current.GetAttribute("EquatorialRadius", ""));
                    string layerDirectory = worldIter.Current.GetAttribute("LayerDirectory", "");

                    if (layerDirectory.IndexOf(":") < 0)
                    {
                        layerDirectory = Path.Combine(Path.GetDirectoryName(filename), layerDirectory);
                    }

                    TerrainAccessor[] terrainAccessor = getTerrainAccessorsFromXPathNodeIterator(worldIter.Current.Select("TerrainAccessor"),
                        System.IO.Path.Combine(cache.CacheDirectory, worldName));

                    World newWorld = new World(
                        worldName,
                        new Microsoft.DirectX.Vector3(0, 0, 0),
                        new Microsoft.DirectX.Quaternion(0, 0, 0, 0),
                        equatorialRadius,
                        cache.CacheDirectory,
                        (terrainAccessor != null ? terrainAccessor[0] : null)//TODO: Oops, World should be able to handle an array of terrainAccessors
                        );

                    //加载所有要渲染绘制的对象
                    newWorld.RenderableObjects = getRenderablesFromLayerDirectory(layerDirectory, newWorld, cache);

                    return newWorld;
                }
            }
            catch (XmlSchemaException ex)
            {
                Log.Write(Log.Levels.Error, "CONF", "Exception caught during XML parsing: " + ex.Message);
                Log.Write(Log.Levels.Error, "CONF", "File " + filename + " was not read successfully.");
                // TODO: should pop up a message box or something.
                return null;
            }

            return null;
        }

 ——》170 public static RenderableObjectList getRenderableFromLayerFile(string layerFile, World parentWorld, Cache cache, bool enableRefresh)方法，真正加载绘制对象集合的函数。

　　3.2绘制所有要绘制的对象
　　WorldWind.cs中MainAppliaction()中
——》675worldWindow.Render();调用了WorldWindow.cs的Render()方法
——》785 m_World.Render(this.drawArgs);调用World.cs的public override void Render(DrawArgs drawArgs)方法

分类分层次地调用渲染代码 


Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> public override void Render(DrawArgs drawArgs)
        {
            try
            {

                if (m_WorldSurfaceRenderer != null && World.Settings.UseWorldSurfaceRenderer)
                {
                    m_WorldSurfaceRenderer.RenderSurfaceImages(drawArgs);
                }

                //  Old method -- problems with RenderPriority sorting
                //    RenderableObjects.Render(drawArgs);

                RenderStars(drawArgs, RenderableObjects);

                if (drawArgs.CurrentWorld.IsEarth && World.Settings.EnableAtmosphericScattering)
                {
                    float aspectRatio = (float)drawArgs.WorldCamera.Viewport.Width / drawArgs.WorldCamera.Viewport.Height;
                    float zNear = (float)drawArgs.WorldCamera.Altitude * 0.1f;
                    double distToCenterOfPlanet = (drawArgs.WorldCamera.Altitude + equatorialRadius);
                    double tangentalDistance = Math.Sqrt(distToCenterOfPlanet * distToCenterOfPlanet - equatorialRadius * equatorialRadius);
                    double amosphereThickness = Math.Sqrt(m_outerSphere.m_radius * m_outerSphere.m_radius + equatorialRadius * equatorialRadius);
                    Matrix proj = drawArgs.device.Transform.Projection;
                    drawArgs.device.Transform.Projection = Matrix.PerspectiveFovRH((float)drawArgs.WorldCamera.Fov.Radians, aspectRatio, zNear, (float)(tangentalDistance + amosphereThickness));
                    drawArgs.device.RenderState.ZBufferEnable = false;
                    drawArgs.device.RenderState.CullMode = Cull.CounterClockwise;
                    m_outerSphere.Render(drawArgs);
                    drawArgs.device.RenderState.CullMode = Cull.Clockwise;
                    drawArgs.device.RenderState.ZBufferEnable = true;

                    drawArgs.device.Transform.Projection = proj;
                }

                if (World.Settings.EnableSunShading)
                    RenderSun(drawArgs);
                //分类、分层次地调用渲染方法
                //render SurfaceImages
                Render(RenderableObjects, WorldWind.Renderable.RenderPriority.TerrainMappedImages, drawArgs);

                if (m_projectedVectorRenderer != null)
                    m_projectedVectorRenderer.Render(drawArgs);

                //render AtmosphericImages
                Render(RenderableObjects, WorldWind.Renderable.RenderPriority.AtmosphericImages, drawArgs);

                //render LinePaths
                Render(RenderableObjects, WorldWind.Renderable.RenderPriority.LinePaths, drawArgs);

                //render Placenames
                Render(RenderableObjects, WorldWind.Renderable.RenderPriority.Placenames, drawArgs);

                //render Icons
                Render(RenderableObjects, WorldWind.Renderable.RenderPriority.Icons, drawArgs);

                //render Custom
                Render(RenderableObjects, WorldWind.Renderable.RenderPriority.Custom, drawArgs);

                if (Settings.showPlanetAxis)
                    this.DrawAxis(drawArgs);
            }
            catch (Exception ex)
            {
                Log.Write(ex);
            }
        }

 

——》分类绘制过程中是调用 485行的private void Render(WorldWind.Renderable.RenderableObject renderable, WorldWind.Renderable.RenderPriority priority, DrawArgs drawArgs)方法。

 

被各类对象调用的渲染方法 


Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->private void Render(WorldWind.Renderable.RenderableObject renderable, WorldWind.Renderable.RenderPriority priority, DrawArgs drawArgs)
        {
            if (!renderable.IsOn || (renderable.Name != null && renderable.Name.Equals("Starfield")))
                return;

            try
            {
                if (priority == WorldWind.Renderable.RenderPriority.Icons && renderable is Icons)
                {
　　　　　　　　　　　//关键代码,真正调用DirectX实施渲染绘制的，Render（）方法被RenderObject类的子类渲染对象重载，实际上调用的是子类的Render()方法。 
                   renderable.Render(drawArgs);
                }
                else if (renderable is WorldWind.Renderable.RenderableObjectList)
                {
                    WorldWind.Renderable.RenderableObjectList rol = (WorldWind.Renderable.RenderableObjectList)renderable;
                    for (int i = 0; i < rol.ChildObjects.Count; i++)
                    {
                        Render((WorldWind.Renderable.RenderableObject)rol.ChildObjects[i], priority, drawArgs);
                    }
                }
                // hack at the moment
                else if (priority == WorldWind.Renderable.RenderPriority.TerrainMappedImages)
                {
                    if (renderable.RenderPriority == WorldWind.Renderable.RenderPriority.SurfaceImages || renderable.RenderPriority == WorldWind.Renderable.RenderPriority.TerrainMappedImages)
                    {
                        renderable.Render(drawArgs);
                    }
                }
                else if (renderable.RenderPriority == priority)
                {
                    renderable.Render(drawArgs);
                }
            }
            catch (Exception ex)
            {
                Log.Write(ex);
            }
        }

 

说明：该方法中596行 renderable.Render(drawArgs);实质上是调用各个RenderableObject具体的子类重写的Render()方法，实现绘制的。

　　4.以WavingFlagLayer.cs类重写的588行Render()方法为例，看看是如何完成绘制的。

WavingFlagLayer类渲染代码 


Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> public override void Render(DrawArgs drawArgs)
        {
            if (!isInitialized)
                return;
            if (m_polygonFeature == null || !drawArgs.WorldCamera.ViewFrustum.Intersects(m_polygonFeature.BoundingBox))
                return;
            try
            {
                double offset = 0;

                if (Bar3D != null && Bar3D.IsOn)
                {

                    Bar3D.Render(drawArgs);
                    offset = Bar3D.RenderedHeight;

                }

                Cull cull = drawArgs.device.RenderState.CullMode;

                drawArgs.device.RenderState.CullMode = Cull.None;

                drawArgs.device.RenderState.ZBufferEnable = true;

                drawArgs.device.TextureState[0].ColorOperation = TextureOperation.SelectArg1;

                drawArgs.device.TextureState[0].ColorArgument1 = TextureArgument.TextureColor;

                Vector3 surfacePos = MathEngine.SphericalToCartesian(m_latitude, m_longitude, World.EquatorialRadius);

                Vector3 rc = new Vector3(

                    (float)drawArgs.WorldCamera.ReferenceCenter.X,

                    (float)drawArgs.WorldCamera.ReferenceCenter.Y,

                    (float)drawArgs.WorldCamera.ReferenceCenter.Z

                    );

                Vector3 projectedPoint = drawArgs.WorldCamera.Project(surfacePos - rc);

                int mouseBuffer = 15;
                if (projectedPoint.X > DrawArgs.LastMousePosition.X - mouseBuffer &&

                        projectedPoint.X < DrawArgs.LastMousePosition.X + mouseBuffer &&

                        projectedPoint.Y > DrawArgs.LastMousePosition.Y - mouseBuffer &&

                        projectedPoint.Y < DrawArgs.LastMousePosition.Y + mouseBuffer)
                {

                    if (!m_isMouseInside)
                    {

                        m_isMouseInside = true;

                        if (OnMouseEnterEvent != null)
                        {

                            OnMouseEnterEvent(this, null);

                        }

                    }

                }

                else
                {

                    if (m_isMouseInside)
                    {

                        m_isMouseInside = false;

                        if (OnMouseLeaveEvent != null)
                        {

                            OnMouseLeaveEvent(this, null);

                        }

                    }

                }

                drawArgs.device.RenderState.CullMode = Cull.None;

                if (ShowHighlight)

                    renderHighlight(drawArgs);

                RenderFlag(drawArgs, offset);

                drawArgs.device.RenderState.CullMode = cull;

            }

            catch (Exception ex)
            {

                Log.Write(ex);

            }

        }