学习WW有一段时间了，但是若想开发自己基于WW的插件，必然会遇到RendableObject中的DirectX渲染问题，
WorldWind系列十：RendableObject中的DirectX渲染分析：ImageLaye
。所有需要渲染绘制的 WW三维插件，最终是通过继承RendableObject并实现自己的Initialize()、Update()、Render()方法的。想写自己的Render()方法不是简单的事情，你必然要学习DirectX编程，否则，你连看懂示例中的底层Render()方法都很难，谈何开发自己的插件。为了突破DirectX编程对我学习WW插件的阻挠，我“快餐式”地突击学习了DirectX，对基本流程和基本原理有了一定认识。今天下午我也对BMNG插件中RendableObject子类——ImageLayer为例进行了分析学习。现在与大家分享一下。
注：请务必先学过
Direct3D学习（资料收集），否则看下面的内容无异于浪费你宝贵的时间。
Image Layer重载实现的Initialize（）方法。
Initialize方法代码
///
/// Layer initialization code
///
public override void Initialize(DrawArgs drawArgs)
{
try
{
//获取绘制设备对象
this.device = drawArgs.device;
if(_imagePath == null && _imageUrl != null && _imageUrl.ToLower().StartsWith("http://"))
{
//根据URL地址，在本地构建同样层次的文件夹路径。这里有个知识点getFilePathFromUrl（）方法，自己定位学习
_imagePath = getFilePathFromUrl(_imageUrl);
}
FileInfo imageFileInfo = null;
if(_imagePath != null)
imageFileInfo = new FileInfo(_imagePath);
if(downloadThread != null && downloadThread.IsAlive)
return;
if(_imagePath != null &&
cacheExpiration != TimeSpan.MaxValue &&
cacheExpiration.TotalMilliseconds > 0 &&
_imageUrl.ToLower().StartsWith("http://") &&
imageFileInfo != null &&
imageFileInfo.Exists &&
imageFileInfo.LastWriteTime < System.DateTime.Now - cacheExpiration)
{
//attempt to redownload it
//启用新线程，下载影像图片。我稍后分析DownloadImage（）方法，是重点之一
downloadThread = new Thread(new ThreadStart(DownloadImage));
downloadThread.Name = "ImageLayer.DownloadImage";
downloadThread.IsBackground = true;
downloadThread.Start();
return;
}
if(m_TextureStream != null)
{
//从文件流中，更新Texture(纹理)，重点分析
UpdateTexture(m_TextureStream, m_TransparentColor);
verticalExaggeration = World.Settings.VerticalExaggeration;
//创建Mesh,稍后重点分析
CreateMesh();
isInitialized = true;
return;
}
else if(imageFileInfo != null && imageFileInfo.Exists)
{
//从文件路径中更新纹理
UpdateTexture(_imagePath);
verticalExaggeration = World.Settings.VerticalExaggeration;
//创建格网Mesh,为了获取Vertex集合。
CreateMesh();
isInitialized = true;
return;
}
if(_imageUrl != null && _imageUrl.ToLower().StartsWith("http://"))
{
//download it...
downloadThread = new Thread(new ThreadStart(DownloadImage));
downloadThread.Name = "ImageLayer.DownloadImage";
downloadThread.IsBackground = true;
downloadThread.Start();
return;
}
// No image available
Dispose();
isOn = false;
return;
}
catch
{
}
}
398行
DownloadImage（）
方法中关键代码分析学习
关键代码
//WW中负责从Web下载文件（影像和配置文件）的类WebDownload 。（写的很好，可以被我们重用。这里是个知识点，感兴趣地自己学习）
using(WebDownload downloadReq = new WebDownload(this._imageUrl))
{
downloadReq.ProgressCallback += new DownloadProgressHandler(UpdateDownloadProgress);
string filePath = getFilePathFromUrl(_imageUrl);
if(_imagePath==null)
{
// Download to RAM
//将下载的文件放到内存中，然后ImageHelper类从流对象加载转变为纹理对象。
downloadReq.DownloadMemory();
texture = ImageHelper.LoadTexture(downloadReq.ContentStream);
}
else
{
//将加载的文件保存到——imagePath中，然后加载更新纹理
downloadReq.DownloadFile(_imagePath);
UpdateTexture(_imagePath);
}
//创建Mesh(我是自学DirectX,搞不清Mesh该翻译成啥，但我知道是干啥用的)
CreateMesh();
isInitialized = true;
}
ImageHelper中加载纹理的函数真正实现是191行public static Texture LoadTexture(Stream textureStream, int colorKey)。
从流中加载纹理代码
public static Texture LoadTexture(Stream textureStream, int colorKey)
{
try
{
//Direct3D的TextureLoader类的FromStream，从流对象中创建纹理
Texture texture = TextureLoader.FromStream(DrawArgs.Device, textureStream, 0, 0,
1, Usage.None, World.Settings.TextureFormat, Pool.Managed, Filter.Box, Filter.Box, colorKey);
return texture;
}
catch (Microsoft.DirectX.Direct3D.InvalidDataException)
{
}
try
{
// DirectX failed to load the file, try GDI+
// Additional formats supported by GDI+: GIF, TIFF
// TODO: Support color keying. See: System.Drawing.Imaging.ImageAttributes
如果DirectX创建纹理失败，则使用GDI+通过创建Image来实现创建纹理
using (Bitmap image = (Bitmap)Image.FromStream(textureStream))
{
//学过DirectX,下面创建纹理的方法在Demo中很常见（一定要先学DirectX编程）
Texture texture = new Texture(DrawArgs.Device, image, Usage.None, Pool.Managed);
return texture;
}
}
catch
{
throw new Microsoft.DirectX.Direct3D.InvalidDataException("Error reading image stream.");
}
}
通过文件路径中加载纹理，最终也是调用上面的方法，只是先通过文件路径，将文件打开创建了流对象。请看ImageHelper.cs中52行 public static Texture LoadTexture(string textureFileName, int colorKey)。
public static Texture LoadTexture(string textureFileName, int colorKey)
{
try
{
//将文件打开创建了流对象,从影像流中创建纹理
using (Stream imageStream = File.OpenRead(textureFileName))
return LoadTexture(imageStream, colorKey);
}
catch
{
throw new Microsoft.DirectX.Direct3D.InvalidDataException(string.Format("Error reading image file '{0}'.", textureFileName));
}
}
ImageLayer.cs中的956行代码UpdateTexture(string fileName)更新纹理方法，关键代码Texture newTexture = ImageHelper.LoadTexture(fileName);就是从文件路径中创新新的纹理对象，上面已经分析过了，不再赘述。
CreateMesh()方法分析
该方法是最关键的，它创建了Device最终渲染三角面列表所需要的点集合，即 protected CustomVertex.PositionNormalTextured[] vertices;其中CustomVertex.PositionNormalTextured是点类型，就是说所要绘制的点是带纹理的带法线的。（如果要问为什么要这样，那请你先学习好DirectX编程）
构建Mesh代码
protected virtual void CreateMesh()
{
int upperBound = meshPointCount - 1;
float scaleFactor = (float)1/upperBound;
double latrange = Math.Abs(maxLat - minLat);
double lonrange;
if(minLon < maxLon)
lonrange = maxLon - minLon;
else
lonrange = 360.0f + maxLon - minLon;
int pacityColor = System.Drawing.Color.FromArgb(this.m_opacity,0,0,0).ToArgb();
//创建点集合对象vertices，大小为64*64个
vertices = new CustomVertex.PositionNormalTextured[meshPointCount * meshPointCount];
for(int i = 0; i < meshPointCount; i++)
{
for(int j = 0; j < meshPointCount; j++)
{
double height = 0;
if(this._terrainAccessor != null)
height = this.verticalExaggeration * this._terrainAccessor.GetElevationAt(
(double)maxLat - scaleFactor * latrange * i,
(double)minLon + scaleFactor * lonrange * j,
(double)upperBound / latrange);
//将空间坐标转换为矢量坐标（即经纬度和半径，转为X\Y\Z）
Vector3 pos = MathEngine.SphericalToCartesian(
maxLat - scaleFactor*latrange*i,
minLon + scaleFactor*lonrange*j,
layerRadius + height);
//获取点的X,Y,Z Tu Tv
vertices[i*meshPointCount + j].X = pos.X;
vertices[i*meshPointCount + j].Y = pos.Y;
vertices[i*meshPointCount + j].Z = pos.Z;
vertices[i*meshPointCount + j].Tu = j*scaleFactor;
vertices[i*meshPointCount + j].Tv = i*scaleFactor;
// vertices[i*meshPointCount + j].Color = opacityColor;
}
}
//下面的代码是将上面的vertices集合，构建成6个一组，电脑资料
《WorldWind系列十：RendableObject中的DirectX渲染分析：ImageLaye》(https://www.unjs.com)。（注：DirectX中
绘制面
是绘制两个三角形，是要存六个点的）
indices = new short[2 * upperBound * upperBound * 3];
for(int i = 0; i < upperBound; i++)
{
for(int j = 0; j < upperBound; j++)
{
indices[(2*3*i*upperBound) + 6*j] = (short)(i*meshPointCount + j);
indices[(2*3*i*upperBound) + 6*j + 1] = (short)((i+1)*meshPointCount + j);
indices[(2*3*i*upperBound) + 6*j + 2] = (short)(i*meshPointCount + j+1);
indices[(2*3*i*upperBound) + 6*j + 3] = (short)(i*meshPointCount + j+1);
indices[(2*3*i*upperBound) + 6*j + 4] = (short)((i+1)*meshPointCount + j);
indices[(2*3*i*upperBound) + 6*j + 5] = (short)((i+1)*meshPointCount + j+1);
}
}
//计算面的法向量（是重点，高等数学好的话，可以自己学习一下，看看如何求的单位法向量），不想看，调用该方法就行，知道干啥用和怎么用就行啦
calculate_normals(ref vertices, indices);
}
Render()方法分析
ImageLayer.cs中651行
Render()代码
public override void Render(DrawArgs drawArgs)
{
if(downloadThread != null && downloadThread.IsAlive)
//DirectX知识点，可以学习一下
RenderProgress(drawArgs);
if(!this.isInitialized)
return;
try
{
if(texture == null || m_SurfaceImage != null)
return;
//这里是DirectX渲染的关键点之一，
设置渲染纹理。
drawArgs.device.SetTexture(0, this.texture);
if(this._disableZbuffer)
{
if(drawArgs.device.RenderState.ZBufferEnable)
drawArgs.device.RenderState.ZBufferEnable = false;
}
else
{
if(!drawArgs.device.RenderState.ZBufferEnable)
drawArgs.device.RenderState.ZBufferEnable = true;
}
drawArgs.device.RenderState.ZBufferEnable = true;
drawArgs.device.Clear(ClearFlags.ZBuffer, 0, 1.0f, 0);
//设置device.Transform.World
drawArgs.device.Transform.World = Matrix.Translation(
(float)-drawArgs.WorldCamera.ReferenceCenter.X,
(float)-drawArgs.WorldCamera.ReferenceCenter.Y,
(float)-drawArgs.WorldCamera.ReferenceCenter.Z
);
//设置顶点格式为CustomVertex.PositionNormalTextured.Format
device.VertexFormat = CustomVertex.PositionNormalTextured.Format;
//device.DeviceCaps.PixelShaderVersion.Major 获取DirectX中Device的PixelShaderVersion实现主版本号，可以学习一下（device.DeviceCaps）
if (!RenderGrayscale || (device.DeviceCaps.PixelShaderVersion.Major < 1))
{
if (World.Settings.EnableSunShading)
{
//获取太阳在三维空间的照射位置点
Point3d sunPosition = SunCalculator.GetGeocentricPosition(TimeKeeper.CurrentTimeUtc);
//转换为笛卡尔坐标系下的矢量点
Vector3 sunVector = new Vector3(
(float)sunPosition.X,
(float)sunPosition.Y,
(float)sunPosition.Z);
//以下都是设置Device的渲染参数的，DirectX编程中很常见的
//使用灯光
device.RenderState.Lighting = true;
Material material = new Material();
material.Diffuse = System.Drawing.Color.White;
material.Ambient = System.Drawing.Color.White;
//设置材料Material
device.Material = material;
device.RenderState.AmbientColor = World.Settings.ShadingAmbientColor.ToArgb(); //使用法向量
device.RenderState.NormalizeNormals = true;
device.RenderState.AlphaBlendEnable = true;
//设置灯光参数
device.Lights[0].Enabled = true;
device.Lights[0].Type = LightType.Directional;
device.Lights[0].Diffuse = System.Drawing.Color.White;
//灯光方向，来自太阳
device.Lights[0].Direction = sunVector;
//设置纹理参数
device.TextureState[0].ColorOperation = TextureOperation.Modulate;
device.TextureState[0].ColorArgument1 = TextureArgument.Diffuse;
device.TextureState[0].ColorArgument2 = TextureArgument.TextureColor;
}
else
{
device.RenderState.Lighting = false;
device.RenderState.Ambient = World.Settings.StandardAmbientColor;
drawArgs.device.TextureState[0].ColorOperation = TextureOperation.SelectArg1;
drawArgs.device.TextureState[0].ColorArgument1 = TextureArgument.TextureColor;
}
device.RenderState.TextureFactor = System.Drawing.Color.FromArgb(m_opacity, 0, 0, 0).ToArgb();
device.TextureState[0].AlphaOperation = TextureOperation.BlendFactorAlpha;
device.TextureState[0].AlphaArgument1 = TextureArgument.TextureColor;
device.TextureState[0].AlphaArgument2 = TextureArgument.TFactor;
drawArgs.device.VertexFormat = CustomVertex.PositionNormalTextured.Format;
//Device实现渲染绘制,调用的是DrawIndexedUserPrimitives。（如果看不懂，请参考DirectX编程相关知识）
drawArgs.device.DrawIndexedUserPrimitives(PrimitiveType.TriangleList, 0,
vertices.Length, indices.Length / 3, indices, true, vertices);
}
else
{
//以下是使用Effect绘制的
if (grayscaleEffect == null)
{
device.DeviceReset += new EventHandler(device_DeviceReset);
device_DeviceReset(device, null);
}
//设置Effect对象参数
grayscaleEffect.Technique = "RenderGrayscaleBrightness";
grayscaleEffect.SetValue("WorldViewProj", Matrix.Multiply(device.Transform.World, Matrix.Multiply(device.Transform.View, device.Transform.Projection)));
grayscaleEffect.SetValue("Tex0", texture);
grayscaleEffect.SetValue("Brightness", GrayscaleBrightness);
float pacity = (float)m_opacity / 255.0f;
grayscaleEffect.SetValue("Opacity", opacity);
//以下是Effect渲染的关键
int numPasses = grayscaleEffect.Begin(0);
for (int i = 0; i < numPasses; i++)
{
grayscaleEffect.BeginPass(i);
drawArgs.device.DrawIndexedUserPrimitives(PrimitiveType.TriangleList, 0,
vertices.Length, indices.Length / 3, indices, true, vertices);
grayscaleEffect.EndPass();
}
grayscaleEffect.End();
}
drawArgs.device.Transform.World = drawArgs.WorldCamera.WorldMatrix;
}
finally
{
if (m_opacity < 255)
{
// Restore alpha blend state
device.RenderState.SourceBlend = Blend.SourceAlpha;
device.RenderState.DestinationBlend = Blend.InvSourceAlpha;
}
if(this._disableZbuffer)
drawArgs.device.RenderState.ZBufferEnable = true;
}
}
我想通过分析上面的，让大家看看Render()方法渲染的流程，里面的具体渲染知识点大家可以参看一些DirectX编程。因为Update()函数中调用的方法在上面都有介绍，所以就不再另外分析啦。希望对大家深入了解学习WW插件渲染有帮助。