WorldWind学习系列六：渲染过程解析篇

WorldWind学习系列六：渲染过程解析篇

　　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

　　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：

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

　　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




加载渲染对象代码

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。




分类分层次地调用渲染代码

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

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

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);

}

}

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



　　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。