Ogre TerrainGroup地形賞析
1.1 參考
http://www.ogre3d.org/tikiwiki/tiki-index.php?page=Ogre+Terrain+System
http://www.ogre3d.org/tikiwiki/tiki-index.php?page=Ogre+Terrain+Component+FAQ
New Terrain Early Shots
http://www.ogre3d.org/forums/viewtopic.php?f=11&t=50674
http://tulrich.com/geekstuff/sig-notes.pdf
ogre_src_v1-8-1\Components\Terrain
├─include
│ OgreTerrain.h
│ OgreTerrainGroup.h
│ OgreTerrainLayerBlendMap.h
│ OgreTerrainMaterialGenerator.h
│ OgreTerrainMaterialGeneratorA.h
│ OgreTerrainPagedWorldSection.h
│ OgreTerrainPaging.h
│ OgreTerrainPrerequisites.h
│ OgreTerrainQuadTreeNode.h
│
└─src
OgreTerrain.cpp
OgreTerrainGroup.cpp
OgreTerrainLayerBlendMap.cpp
OgreTerrainMaterialGenerator.cpp
OgreTerrainMaterialGeneratorA.cpp
OgreTerrainPagedWorldSection.cpp
OgreTerrainPaging.cpp
OgreTerrainQuadTreeNode.cpp
Sample
ogre_src_v1-8-1\Samples\Terrain
1.2 類圖
<帖不了圖圖>
1.3 使用流程
1、首先需要創(chuàng)建terrain options
TerrainGlobalOptions* mTerrainGlobals;
TerrainGroup* mTerrainGroup;
mTerrainGlobals = OGRE_NEW TerrainGlobalOptions();
mTerrainGlobals->setMaxPixelError(8);
mTerrainGlobals->setCompositeMapDistance(3000);
mTerrainGlobals->setLightMapDirection(l->getDerivedDirection());
mTerrainGlobals->setCompositeMapAmbient(mSceneMgr->getAmbientLight());
mTerrainGlobals->setCompositeMapDiffuse(l->getDiffuseColour());
2、其次要創(chuàng)建TerrainGroup對象
mTerrainGroup = OGRE_NEW Ogre::TerrainGroup(mSceneMgr, Ogre::Terrain::ALIGN_X_Z, 513, 12000.0f);
mTerrainGroup->setFilenameConvention(Ogre::String("BasicTutorial3Terrain"), Ogre::String("dat"));
mTerrainGroup->setOrigin(Ogre::Vector3::ZERO);
3、然后設(shè)置Terrain Group
// Configure default import settings for if we use imported image
Terrain::ImportData& defaultimp = mTerrainGroup->getDefaultImportSettings();
defaultimp.terrainSize = TERRAIN_SIZE;
defaultimp.worldSize = TERRAIN_WORLD_SIZE;
defaultimp.inputScale = 600;
defaultimp.minBatchSize = 33;
defaultimp.maxBatchSize = 65;
// textures
defaultimp.layerList.resize(3);
defaultimp.layerList[0].worldSize = 100;
defaultimp.layerList[0].textureNames.push_back("dirt_grayrocky_diffusespecular.dds");
defaultimp.layerList[0].textureNames.push_back("dirt_grayrocky_normalheight.dds");
defaultimp.layerList[1].worldSize = 30;
defaultimp.layerList[1].textureNames.push_back("grass_green-01_diffusespecular.dds");
defaultimp.layerList[1].textureNames.push_back("grass_green-01_normalheight.dds");
defaultimp.layerList[2].worldSize = 200;
defaultimp.layerList[2].textureNames.push_back("growth_weirdfungus-03_diffusespecular.dds");
defaultimp.layerList[2].textureNames.push_back("growth_weirdfungus-03_normalheight.dds");
4、最后執(zhí)行加載
mTerrainGroup->loadAllTerrains(true)
后續(xù)需要計算blendmaps
6、清理Terrain Group
mTerrainGroup->freeTemporaryResources();
Terrain Group是Terrain的集合，如此可以取到集合里的terrain：
TerrainGroup::TerrainIterator ti = mTerrainGroup->getTerrainIterator();
while(ti.hasMoreElements())
{
Terrain* t = ti.getNext()->instance;
}
至此完成了ogre最新的TerrainGroup的生命周期。
1.4 地形文件
1.4.1 Terrain文件格式
TerrainData (Identifier 'TERR')
[Version 1]
|
Name
|
Type
|
Description
|
|
Terrain orientation
|
uint8
|
The orientation of the terrain; XZ = 0, XY = 1, YZ = 2
|
|
Terrain size
|
uint16
|
The number of vertices along one side of the terrain
|
|
Terrain world size
|
Real
|
The world size of one side of the terrain
|
|
Max batch size
|
uint16
|
The maximum batch size in vertices along one side
|
|
Min batch size
|
uint16
|
The minimum batch size in vertices along one side
|
|
Position
|
Vector3
|
The location of the centre of the terrain
|
|
Height data
|
float[size*size]
|
List of floating point heights
|
|
LayerDeclaration
|
LayerDeclaration*
|
The layer declaration for this terrain (see below)
|
|
Layer count
|
uint8
|
The number of layers in this terrain
|
|
LayerInstance list
|
LayerInstance*
|
A number of LayerInstance definitions based on layer count (see below)
|
|
Layer blend map size
|
uint16
|
The size of the layer blend maps as stored in this file
|
|
Packed blend texture data
|
uint8*
|
layerCount-1 sets of blend texture data interleaved as either RGB or RGBA depending on layer count
|
|
Optional derived map data
|
TerrainDerivedMap list
|
0 or more sets of map data derived from the original terrain
|
|
Delta data
|
float[size*size]
|
At each vertex, delta information for the LOD at which this vertex disappears
|
|
Quadtree delta data
|
float[quadtrees*lods]
|
At each quadtree node, for each lod a record of the max delta value in the region
|
TerrainLayerDeclaration (Identifier 'TDCL')
[Version 1]
TerrainLayerSampler (Identifier 'TSAM')
[Version 1]
|
Name
|
Type
|
Description
|
|
Alias
|
String
|
Alias name of this sampler
|
|
Format
|
uint8
|
Desired pixel format
|
TerrainLayerSamplerElement (Identifier 'TSEL')
[Version 1]
|
Name
|
Type
|
Description
|
|
Source
|
uint8
|
Sampler source index
|
|
Semantic
|
uint8
|
Semantic interpretation of this element
|
|
Element start
|
uint8
|
Start of this element in the sampler
|
|
Element count
|
uint8
|
Number of elements in the sampler used by this entry
|
LayerInstance (Identifier 'TLIN')
[Version 1]
|
Name
|
Type
|
Description
|
|
World size
|
Real
|
The world size of this layer (determines UV scaling)
|
|
Texture list
|
String*
|
List of texture names corresponding to the number of samplers in the layer declaration
|
TerrainDerivedData (Identifier 'TDDA')
[Version 1]
|
Name
|
Type
|
Description
|
|
Derived data type name
|
String
|
Name of the derived data type ('normalmap', 'lightmap', 'colourmap', 'compositemap')
|
|
Size
|
uint16
|
Size of the data along one edge
|
|
Data
|
varies based on type
|
The data
|
1.4.2 加載地形文件
OgreTerrain_d.dll!Ogre::Terrain::determineLodLevels
OgreTerrain_d.dll!Ogre::Terrain::prepare
OgreTerrain_d.dll!Ogre::Terrain::prepare
OgreTerrain_d.dll!Ogre::TerrainGroup::handleRequest
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::RequestHandlerHolder::handleRequest
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::processRequest
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::processRequestResponse
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::addRequest
OgreTerrain_d.dll!Ogre::TerrainGroup::loadTerrainImpl
OgreTerrain_d.dll!Ogre::TerrainGroup::loadAllTerrains
Sample_Terrain_d.dll!Sample_Terrain::setupContent
首先加載全局選項TerrainGlobalOptions
然后從本地terrain文件中讀取(@Terrain::prepare)
18:12:36: DefaultWorkQueueBase('Root') - QUEUED(thread:main): ID=1 channel=1 requestType=1
18:12:36: DefaultWorkQueueBase('Root') - PROCESS_REQUEST_START(main): ID=1 channel=1 requestType=1
18:12:36: Terrain created; size=513 minBatch=33 maxBatch=65 treeDepth=4 lodLevels=5 leafLods=2
18:12:36: Terrain::distributeVertexData processing source terrain size of 513
18:12:36: Assigning vertex data, resolution=513 startDepth=2 endDepth=4 splits=4
18:12:36: Assigning vertex data, resolution=129 startDepth=0 endDepth=2 splits=1
18:12:36: Terrain::distributeVertexData finished
18:12:36: DefaultWorkQueueBase('Root') - PROCESS_REQUEST_END(main): ID=1 channel=1 requestType=1 processed=1
18:12:36: DefaultWorkQueueBase('Root') - PROCESS_RESPONSE_START(thread:main): ID=1 success=1 messages=[] channel=1 requestType=1
18:12:36: Font Default/Vera using texture size 512x256
18:12:36: Info: Freetype returned null for character 160 in font Default/Vera
18:12:36: Texture: Default/VeraTexture: Loading 1 faces(PF_BYTE_LA,512x256x1) with 0 generated mipmaps from Image. Internal format is PF_BYTE_LA,512x256x1.
18:12:36: Mesh: Loading axes.mesh.
18:12:36: WARNING: axes.mesh is an older format ([MeshSerializer_v1.30]); you should upgrade it as soon as possible using the OgreMeshUpgrade tool.
18:12:36: Texture: axes.png: Loading 1 faces(PF_R8G8B8,256x256x1) Internal format is PF_X8R8G8B8,256x256x1.
18:12:36: DefaultWorkQueueBase('Root') - PROCESS_RESPONSE_END(thread:main): ID=1 success=1 messages=[] channel=1 requestType=1
1.4.3 地形表面網(wǎng)格
已經(jīng)不存在一個具體的地形表面網(wǎng)格的概念了，地形是“分層分批處理”的東西，地形對象不再擁有一個具體的地形頂點(diǎn)數(shù)據(jù)，這些數(shù)據(jù)是在LODs中的。
http://www.ogre3d.org/forums/viewtopic.php?f=11&t=50674&start=275#p365005
Actually, the Terrain object doesn't hold this information. The terrain is what I call "hierarchically batched" which means there is no set of vertex data at the highest LOD which covers the entire terrain - instead there are a series of hierarchical nodes which each store a specific range of LODs, each of which has a different coverage of the terrain. The only batch which has the whole terrain stored in one are the lowest LOD levels - used when the terrain is very far away. This allows us to efficiently render the entire terrain in one batch when far away, but closer up smaller (physically) batches are used for higher LODs but overall the vertex data for each batch is of the same size (or within a small range). This also allows us to deal with terrains that would be impossible to address with 16-bit indexes - any patch with more than 256 vertices on each side is actually impossible to address as one batch anyway without 32-bit indexes, which I avoid for compatibility. My hierarchical batch system allows very large terrain patches while still respecting 16-bit indexes and generally giving better performance. Unfortunately, it can never be as simple as a single top-level set of vertex data.
So, if I gave you access to what we use internally, I think you'd just be very confused You really do just need to extract the raw heights or just walk across the terrain using getPoint() if you want something 'raw'. I suppose I could provide an API which dumps unindexed full-LOD triangles into a buffer (or maybe with 32-bit indexing), but this will be really inefficient if you then have to re-process the buffer yourself anyway. It's much better just to hook out the points and plug those into your system directly.
1.5 四叉樹結(jié)構(gòu)
每個葉子節(jié)點(diǎn)的size都是允許劃分的批次最大size，也即65。它有2個LodLevel，其size是33，這個LodLevel已經(jīng)是不可劃分的批次最小size了。而非葉子節(jié)點(diǎn)的size都比允許的批次最大size大，并且它只有一個LodLevel，其size也是批次最大size。
由此可見，允許的批次最大和最小size是劃分樹節(jié)點(diǎn)和LodLevel的直接依據(jù)，它們約束了節(jié)點(diǎn)和Lod劃分的頂點(diǎn)尺寸。對于樹節(jié)點(diǎn)，簡單來說劃分的方法是將其平均分割成4塊，如果每塊比允許的批次最大size還要大，則用同樣的方式對它再次遞歸分割。對于Lod來說，如果其所有者樹節(jié)點(diǎn)不是葉子，那這個Lod就讓其大小設(shè)為批次的最大size，否則，就對其進(jìn)行Lod細(xì)分，讓每個Lod盡量的小，但是不能小于批次允許的最小值。
批次最大最小size約束存在的意義是，一方面讓每個lod的頂點(diǎn)盡可能的少，這樣在渲染的時候可以更準(zhǔn)確的找出最少的空間分割塊，以便選擇盡可能少的頂點(diǎn)；另一方面每個Lod的頂點(diǎn)又不能太少，否則會增加顯卡的渲染批次。
+[0]New Node,size:513,lod:4,depth:0,quadrant:0,batch range[33,65]
+[1]New Node,size:257,lod:3,depth:1,quadrant:0,batch range[33,65]
+[2]New Node,size:129,lod:2,depth:2,quadrant:0,batch range[33,65]
+[ 3]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[ 4]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[ 5]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[ 6]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[7]New Node,size:129,lod:2,depth:2,quadrant:1,batch range[33,65]
+[ 8]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[ 9]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[10]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[11]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[12]New Node,size:129,lod:2,depth:2,quadrant:2,batch range[33,65]
+[13]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[14]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[15]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[16]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[17]New Node,size:129,lod:2,depth:2,quadrant:3,batch range[33,65]
+[18]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[19]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[20]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[21]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[22]New Node,size:257,lod:3,depth:1,quadrant:1,batch range[33,65]
+[23]New Node,size:129,lod:2,depth:2,quadrant:0,batch range[33,65]
+[24]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[25]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[26]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[27]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[28]New Node,size:129,lod:2,depth:2,quadrant:1,batch range[33,65]
+[29]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[30]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[31]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[32]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[33]New Node,size:129,lod:2,depth:2,quadrant:2,batch range[33,65]
+[34]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[35]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[36]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[37]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[38]New Node,size:129,lod:2,depth:2,quadrant:3,batch range[33,65]
+[39]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[40]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[41]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[42]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[43]New Node,size:257,lod:3,depth:1,quadrant:2,batch range[33,65]
+[44]New Node,size:129,lod:2,depth:2,quadrant:0,batch range[33,65]
+[45]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[46]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[47]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[48]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[49]New Node,size:129,lod:2,depth:2,quadrant:1,batch range[33,65]
+[50]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[51]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[52]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[53]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[54]New Node,size:129,lod:2,depth:2,quadrant:2,batch range[33,65]
+[55]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[56]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[57]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[58]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[59]New Node,size:129,lod:2,depth:2,quadrant:3,batch range[33,65]
+[60]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[61]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[62]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[63]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[64]New Node,size:257,lod:3,depth:1,quadrant:3,batch range[33,65]
+[65]New Node,size:129,lod:2,depth:2,quadrant:0,batch range[33,65]
+[66]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[67]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[68]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[69]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[70]New Node,size:129,lod:2,depth:2,quadrant:1,batch range[33,65]
+[71]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[72]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[73]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[74]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[75]New Node,size:129,lod:2,depth:2,quadrant:2,batch range[33,65]
+[76]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[77]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[78]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[79]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
+[80]New Node,size:129,lod:2,depth:2,quadrant:3,batch range[33,65]
+[81]New Node,size: 65,lod:1,depth:3,quadrant:0,batch range[33,65]
+[82]New Node,size: 65,lod:1,depth:3,quadrant:1,batch range[33,65]
+[83]New Node,size: 65,lod:1,depth:3,quadrant:2,batch range[33,65]
+[84]New Node,size: 65,lod:1,depth:3,quadrant:3,batch range[33,65]
|
Depth
|
Size
|
LOD
|
節(jié)點(diǎn)數(shù)
|
|
0
|
513
|
4
|
1
|
|
1
|
257
|
3
|
4
|
|
2
|
129
|
2
|
16
|
|
3
|
65
|
1
|
64
|
1.5.1 葉子節(jié)點(diǎn)
葉子節(jié)點(diǎn)的順序如下
每個節(jié)點(diǎn)記錄了一個當(dāng)前節(jié)點(diǎn)的偏移值，這個偏移值是相對于父節(jié)點(diǎn)的繼承偏移方式計算出的數(shù)值，有點(diǎn)類似場景管理器中的Node._getDerivedPosition，也即是相對于當(dāng)前地形的偏移值，準(zhǔn)確來說是相對于當(dāng)前地形左上角的偏移，而不是相對其父節(jié)點(diǎn)。這個偏移值需要注意2點(diǎn)：
u 偏移用+x向下，+y向左的二維坐標(biāo)系計算
u 偏移值與頂點(diǎn)數(shù)有-1差，也即最小的格子（LOD=1）的寬度的整數(shù)倍，當(dāng)前是64。
1.6 預(yù)計算基礎(chǔ)數(shù)據(jù)
首先，預(yù)先計算好一些全局基礎(chǔ)數(shù)據(jù)，例如樹深度，最大Lod，葉子節(jié)點(diǎn)的Lod。見Terrain::determineLodLevels。例如，計算結(jié)果如下：
18:12:36: DefaultWorkQueueBase('Root') - QUEUED(thread:main): ID=1 channel=1 requestType=1
18:12:36: DefaultWorkQueueBase('Root') - PROCESS_REQUEST_START(main): ID=1 channel=1 requestType=1
18:12:36: Terrain created; size=513 minBatch=33 maxBatch=65 treeDepth=4 lodLevels=5 leafLods=2
18:12:36: Terrain::distributeVertexData processing source terrain size of 513
18:12:36: Assigning vertex data, resolution=513 startDepth=2 endDepth=4 splits=4
18:12:36: Assigning vertex data, resolution=129 startDepth=0 endDepth=2 splits=1
18:12:36: Terrain::distributeVertexData finished
18:12:36: DefaultWorkQueueBase('Root') - PROCESS_RESPONSE_END(thread:main): ID=1 success=1 messages=[] channel=1 requestType=1
由于我們預(yù)先定義好了批次中最大最小頂點(diǎn)數(shù)、地形的頂點(diǎn)尺寸（分別是65，33，513），通過這個預(yù)先定義好的值，可以生成一個基于四叉樹的LOD關(guān)系數(shù)據(jù)結(jié)構(gòu)。這個數(shù)據(jù)結(jié)構(gòu)可以“映射”到任意面積尺寸的地形中，例如一個單邊為12000的正方形的地形。
1.7 分配地形頂點(diǎn)
地形定義都取到后，就開始分配地形頂點(diǎn)數(shù)據(jù)了。
OgreTerrain_d.dll!Ogre::Terrain::distributeVertexData
OgreTerrain_d.dll!Ogre::Terrain::prepare
OgreTerrain_d.dll!Ogre::Terrain::prepare
OgreTerrain_d.dll!Ogre::TerrainGroup::handleRequest
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::RequestHandlerHolder::handleRequest
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::processRequest
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::processRequestResponse
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::addRequest
OgreTerrain_d.dll!Ogre::TerrainGroup::loadTerrainImpl
OgreTerrain_d.dll!Ogre::TerrainGroup::loadAllTerrains
Sample_Terrain_d.d
（分配頂點(diǎn)的流程圖...只能看pdf了）
1.7.1 算法思想
現(xiàn)在需要找出如何分配頂點(diǎn)數(shù)據(jù)。我們要兼容16位的索引，這意味著我們最多可以拼湊129x129個地形，即使是松散的拼湊低細(xì)節(jié)的LODs也如此，因為下一個可拼湊數(shù)是257x257，這個數(shù)字太大了，所以不用它。
因此，我們需要將頂點(diǎn)數(shù)據(jù)分割成129塊。主要地磚上創(chuàng)建的的數(shù)目也即表明了它上面的點(diǎn)，如果不使用其他的頂點(diǎn)數(shù)據(jù)我們在樹節(jié)點(diǎn)中就不能在更低的LODs中合并地磚了。例如，使用如上所述的257x257的輸入，頂點(diǎn)數(shù)據(jù)為了適合129x129的范圍將不得不被分為2個（在每個維度上）。這些數(shù)據(jù)可以被樹深度從1開始的所有的樹共享，不過Lods 3-1將會從129x129的稀疏數(shù)據(jù)中采樣，而LOD0將會從所有頂點(diǎn)數(shù)據(jù)中采樣。
然而，最低的LOD4將不能使用同樣的頂點(diǎn)數(shù)據(jù)進(jìn)行處理，因為它需要覆蓋整個地形。這里有2個選擇：在17x17上創(chuàng)建另一組僅用于LOD4的頂點(diǎn)數(shù)據(jù)的，或者在出現(xiàn)樹深度為1的時候用LOD4（例如仍舊分拆），并且沿著每一邊像2x9一樣渲染。
由于渲染非常小的批次不理想，以及頂點(diǎn)總數(shù)本質(zhì)上不會很大，所以創(chuàng)建一個單獨(dú)的頂點(diǎn)集還是有可行性。在出現(xiàn)遙遠(yuǎn)的地形時也將會讓頂點(diǎn)緩存機(jī)制更高效。
我們可能需要一個更大尺寸的例子，因為在這種情況下只有層級1（LOD0）需要使用這種單獨(dú)的頂點(diǎn)數(shù)據(jù)。較高細(xì)節(jié)的地形將會需要多種層次，這里有一個65/33批次設(shè)置的2049x2049的例子：
LODlevels = log2(2049 - 1) - log2(33 - 1) + 1 = 11 - 5 + 1 = 7
TreeDepth = log2((2049 - 1) / (65 - 1)) + 1 = 6
在最多細(xì)節(jié)層次上拆分的頂點(diǎn)數(shù)
(size - 1) / (TERRAIN_MAX_BATCH_SIZE - 1) = 2048 / 128 = 16
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LOD
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0:
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2049
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vertices
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32 x 65
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vertex
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tiles
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(tree depth 5)
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vdata
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0-15
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[129x16]
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LOD
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1:
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1025
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vertices
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32 x 33
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vertex
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tiles
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(tree depth 5)
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vdata
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0-15
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[129x16]
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LOD
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2:
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513
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vertices
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16 x 33
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vertex
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tiles
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(tree depth 4)
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vdata
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0-15
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[129x16]
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LOD
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3:
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257
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vertices
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8 x 33
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vertex
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tiles
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(tree depth 3)
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vdata
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16-17
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[129x2]
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|
LOD
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4:
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129
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vertices
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4 x 33
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vertex
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tiles
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(tree depth 2)
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vdata
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16-17
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[129x2]
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|
LOD
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5:
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65
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vertices
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2 x 33
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vertex
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tiles
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(tree depth 1)
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vdata
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16-17
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[129x2]
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LOD
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6:
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33
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vertices
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1 x 33
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vertex
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tiles
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(tree depth 0)
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vdata
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18
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[33]
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所有的頂點(diǎn)總數(shù)都是一個平方數(shù)，它們正好是沿著一條邊的情形。所以，你可以看到我們需要有3個級別的頂點(diǎn)數(shù)據(jù)來滿足（誠然，相當(dāng)極端）這個情況，并且一共有19個頂點(diǎn)數(shù)據(jù)集。完整的細(xì)節(jié)幾何，129的16個子集（X16）這樣的有完全細(xì)節(jié)的幾何體被用作LODs0-2。 LOD3不能使用這個子集，因為它需要通過這些子集進(jìn)行組合，而且它只有8塊地磚，所以我們需要在每一個頂點(diǎn)數(shù)據(jù)段最大是129個頂點(diǎn)的時候構(gòu)造出另外一個集合來滿足這個情況。因為在這種情況下LOD3需要整個257（X257）個的頂點(diǎn)，所以我們?nèi)匀粚?/span>129分割成2（X2）個集合。雖然這一套集合是好用了，也包括了LOD5，但LOD6需要一個單一且連續(xù)的頂點(diǎn)集，所以我們?yōu)樗鼧?gòu)造了一個33x33的頂點(diǎn)集。
在頂點(diǎn)的數(shù)據(jù)存儲方面，這意味著當(dāng)我們的主要數(shù)據(jù)是：
2049^ 2 =4198401個頂點(diǎn)
最終我們存儲的頂點(diǎn)數(shù)據(jù)是
（16 *129）^ 2+（2* 129）^ 2+ 33^ 2 =4327749個頂點(diǎn)
這相當(dāng)于有3%的頂點(diǎn)冗余，但是為了從分組中減少批次它既必要又值得。此外，在LODs3和6（或樹深度為3和0）中將有機(jī)會釋放被更多細(xì)節(jié)LODs使用的數(shù)據(jù)，這在有巨大的地形的時候很重要。例如，如果我們在中等距離時為LOD0-2釋放（GPU）頂點(diǎn)數(shù)據(jù)，就會為地形節(jié)省平均有98%的內(nèi)存開銷。
1.7.2 頂點(diǎn)數(shù)據(jù)
LODs在當(dāng)前4叉樹節(jié)點(diǎn)構(gòu)造時候被創(chuàng)建，其中有個字段指向頂點(diǎn)數(shù)據(jù)，這個頂點(diǎn)數(shù)據(jù)在讀取地形文件時被創(chuàng)建。
J 創(chuàng)建頂點(diǎn)數(shù)據(jù)
//---------------------------------------------------------------------
void TerrainQuadTreeNode::createGpuIndexData()
{
for (size_t lod = 0; lod < mLodLevels.size(); ++lod)
{
LodLevel* ll = mLodLevels[lod];
if (!ll->gpuIndexData)
{
// clone, using default buffer manager ie hardware
ll->gpuIndexData = OGRE_NEW IndexData();
populateIndexData(ll->batchSize, ll->gpuIndexData);
}
}
}
J 取回頂點(diǎn)數(shù)據(jù)
//---------------------------------------------------------------------
//渲染數(shù)據(jù)
void TerrainQuadTreeNode::getRenderOperation(RenderOperation& op)
{
mNodeWithVertexData->updateGpuVertexData();
op.indexData = mLodLevels[mCurrentLod]->gpuIndexData;
op.operationType = RenderOperation::OT_TRIANGLE_STRIP;
op.useIndexes = true;
op.vertexData = getVertexDataRecord()->gpuVertexData;
}
1.7.3 同步-異步機(jī)制
異步加載機(jī)制是Steven Streeting離開前奉獻(xiàn)的一個重量級模塊Paging的核心功能，Paging的異步加載實(shí)現(xiàn)了一個通用的分頁機(jī)制，目前只知道在地形中有應(yīng)用。但是這個優(yōu)秀的分頁機(jī)制可以在所有時間、幀率、消息、事件、渲染命令出現(xiàn)瓶頸的時候使用其擴(kuò)展的各種靈活策略進(jìn)行異步和有區(qū)分度的分解處理從而降低單幀負(fù)載。其算法思想Steven Streeting在Ogre官網(wǎng)有詳細(xì)闡述，見章節(jié)“Page系統(tǒng)設(shè)計思想”。
為了區(qū)別異步加載給地形帶來的復(fù)雜度，關(guān)閉了異步線程和地形Paging 。
#define OGRE_THREAD_SUPPORT 0
//#define PAGING
Root維護(hù)一個默認(rèn)的工作隊列DefaultWorkQueue，執(zhí)行類似壓入執(zhí)行命令的邏輯用這個工作隊列完成。由于關(guān)閉了異步，壓入請求后會立即執(zhí)行響應(yīng)請求的子程序。
Class DefaultWorkQueue : public DefaultWorkQueueBase
OgreTerrain_d.dll!Ogre::TerrainQuadTreeNode::load
OgreTerrain_d.dll!Ogre::Terrain::load
OgreTerrain_d.dll!Ogre::TerrainGroup::handleResponse
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::processResponse
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::processRequestResponse
OgreMain_d.dll!Ogre::DefaultWorkQueueBase::addRequest
OgreTerrain_d.dll!Ogre::TerrainGroup::loadTerrainImpl
OgreTerrain_d.dll!Ogre::TerrainGroup::loadAllTerrains
Sample_Terrain_d.dll!Sample_Terrain::setupContent
Sample_Terrain_d.dll!OgreBites::SdkSample::_setup
1.8 動態(tài)LOD計算
動態(tài)LOD計算主要目的是通過相機(jī)與四叉樹節(jié)點(diǎn)的相對關(guān)系計算出幾個關(guān)鍵指標(biāo)：
u 當(dāng)前Lod，標(biāo)記當(dāng)前節(jié)點(diǎn)LodLevel中第N個被使用的Lod
u 當(dāng)前節(jié)點(diǎn)是否渲染，標(biāo)記當(dāng)前節(jié)點(diǎn)帶領(lǐng)的子樹是否有節(jié)點(diǎn)需要被渲染
LodLevel定義
Struct LodLevel{
/// Number of vertices rendered down one side (not including skirts)
uint16 batchSize;
/// Index data on the gpu
IndexData* gpuIndexData;
/// Maximum delta height between this and the next lower lod
Real maxHeightDelta;
/// Temp calc area for max height delta
Real calcMaxHeightDelta;
/// The most recently calculated transition distance
Real lastTransitionDist;
/// The cFactor value used to calculate transitionDist
Real lastCFactor;
LodLevel() : gpuIndexData(0), maxHeightDelta(0), calcMaxHeightDelta(0),
lastTransitionDist(0), lastCFactor(0) {}
};
1.8.1 LodLevel數(shù)據(jù)細(xì)節(jié)
一個節(jié)點(diǎn)聚合了4個LOD相關(guān)屬性
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基礎(chǔ)Lod(Base Lod)
|
預(yù)先計算好，最深的葉子節(jié)點(diǎn)是0，然后由內(nèi)向外遞增，且兄弟節(jié)點(diǎn)一樣
|
|
當(dāng)前Lod(Current Lod)
|
動態(tài)計算，@TerrainQuadTreeNode::calculateCurrentLod
|
|
Lod層級(Lod Level)
|
保存Lod對應(yīng)的具體頂點(diǎn)信息，每個節(jié)點(diǎn)“掛”一個或多個LodLevel
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Lod層級列表(Lod Level List)
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|
所有節(jié)點(diǎn)的Lod相關(guān)屬性大部分都是初始化時就計算好，只有當(dāng)前LOD是動態(tài)計算的。非葉子節(jié)點(diǎn)只有一個LodLevel，其頂點(diǎn)數(shù)量(LodLevel.batchSize)是當(dāng)前terrain的批次頂點(diǎn)最小值；非葉子節(jié)點(diǎn)的基礎(chǔ)Lod是父節(jié)點(diǎn)的基礎(chǔ)Lod-1。葉子節(jié)點(diǎn)有多個LodLevel，其數(shù)量是由當(dāng)前terrain預(yù)先計算好(NumLodLevelsPerLeaf)，每個LodLevel中的頂點(diǎn)數(shù)量(LodLevel.batchSize)是當(dāng)前terrain的批次頂點(diǎn)最大值(MaxBatchSize)------與非葉子節(jié)點(diǎn)的情況正好相反;葉子節(jié)點(diǎn)的基礎(chǔ)LOD總是0。
可以看到，節(jié)點(diǎn)的Lod值由內(nèi)從0開始向外逐漸遞增，且同一深度(depth)的節(jié)點(diǎn)Lod也一樣。而每個節(jié)點(diǎn)都會“掛”上一個或多個LodLevel，非葉子節(jié)點(diǎn)只“掛”一個，葉子節(jié)點(diǎn)“掛”多個，這個數(shù)量是有terrain根據(jù)世界尺寸、最大、最小單批次頂點(diǎn)數(shù)等值預(yù)先計算好的。
非葉子節(jié)點(diǎn)“掛”的LodLevel所包含的頂點(diǎn)數(shù)是terrain的允許的單個批次頂點(diǎn)最小數(shù)量。葉子節(jié)點(diǎn)的情況則不同，“掛”的第一個LodLevel所包含的頂點(diǎn)數(shù)是單個批次頂點(diǎn)的最大數(shù)，然后第二個減少一半---實(shí)際情況稍微復(fù)雜，數(shù)量由公式(((sz - 1) * 0.5) + 1)給出，也即幾何學(xué)上的四邊形頂點(diǎn)減半。有點(diǎn)類似D3DX中的層級紋理。
一切都很天衣無縫，只等當(dāng)前Lod動態(tài)計算時，按照特定的規(guī)則決定哪些頂點(diǎn)需要被渲染，也即哪些LodLevel參與渲染。
1.8.2 動態(tài)計算Lod
一般的，Lod表示的值從0開始，依次遞增，越到后面對象的細(xì)節(jié)越少。典型的如層級紋理。在地形中也如此。首先，在整個四叉樹節(jié)點(diǎn)中，每個節(jié)點(diǎn)有自己的Lod，或者叫基礎(chǔ)Lod，這個值是固定的：葉子節(jié)點(diǎn)的Lod占用0~M；兄弟關(guān)系的Lod一樣；非葉子節(jié)點(diǎn)占用1個Lod，從M+1開始，越往樹根走Lod越大。這樣Lod最大的節(jié)點(diǎn)就是樹根了。
動態(tài)計算Lod的關(guān)鍵因素是相機(jī)到節(jié)點(diǎn)中心的距離與節(jié)點(diǎn)中LodLevel的過渡距離，后者好比是一把尺子，用于判斷這個Lod是否可以被相機(jī)可見。計算方法見TerrainQuadTreeNode::calculateCurrentLod。
每幀地形的Lod計算過程是對四叉樹遞歸遍歷的過程。首先遍歷所有子樹，然后在進(jìn)行自身的計算。將計算過錯分解為第一類計算過程和第二類計算過程：
bool TerrainQuadTreeNode::calculateCurrentLod(const Camera* cam, Real cFactor)
{
mSelfOrChildRendered = false;
///------------------------------------------------------------------------
//深度優(yōu)先的遍歷，首先檢查第一個葉子節(jié)點(diǎn)，考察其可見性，然后是兄弟節(jié)點(diǎn)，軟后是父節(jié)點(diǎn)
int childRenderedCount = 0;
if (!isLeaf())
{
for (int i = 0; i < 4; ++i)
{
if (mChildren[i]->calculateCurrentLod(cam, cFactor))
++childRenderedCount;
}
}
//需要渲染的子節(jié)點(diǎn)數(shù)是0,或者是葉子節(jié)點(diǎn)，或者是所有子節(jié)點(diǎn)都不參與渲染的子樹
//所有葉子節(jié)點(diǎn)都不需要渲染，那就只有考察節(jié)點(diǎn)自身是否需要渲染了
if (childRenderedCount == 0)
{
/// 第一類計算過程 ///
}
//當(dāng)前節(jié)點(diǎn)有子節(jié)點(diǎn)參與渲染，那自身就不需要參與渲染了，
//如果需要渲染的子節(jié)點(diǎn)數(shù)量大于或等于4，只需做個標(biāo)記，不用再計算當(dāng)前節(jié)點(diǎn)了
else
{
/// 第二類計算過程 ///
//跳過自身的渲染
mCurrentLod = -1;
//當(dāng)前子樹需要被渲染
mSelfOrChildRendered = true;
//只考慮需要渲染的子節(jié)點(diǎn)小于4的情形
if (childRenderedCount < 4)
{
// only *some* children decided to render on their own, but either
// none or all need to render, so set the others manually to their lowest
for (int i = 0; i < 4; ++i)
{
TerrainQuadTreeNode* child = mChildren[i];
if (!child->isSelfOrChildRenderedAtCurrentLod())
{
child->setCurrentLod(child->getLodCount()-1);
child->setLodTransition(1.0);
}
}
} // (childRenderedCount < 4)
} // (childRenderedCount == 0)
}
1.8.3 LOD第一類計算過程
// no children were within their LOD ranges, so we should consider our own
Vector3 localPos = cam->getDerivedPosition() - mLocalCentre - mTerrain->getPosition();
//相機(jī)到當(dāng)前節(jié)點(diǎn)中心的絕對距離
Real dist = localPos.length();
dist -= (mBoundingRadius * 0.5f);
// For each LOD, the distance at which the LOD will transition *downwards*
// is given by
// distTransition = maxDelta * cFactor;
uint lodLvl = 0;
mCurrentLod = -1;
for (LodLevelList::iterator i = mLodLevels.begin(); i != mLodLevels.end(); ++i, ++lodLvl)
{
// If we have no parent, and this is the lowest LOD, we always render
// this is the 'last resort' so to speak, we always enoucnter this last
if (lodLvl+1 == mLodLevels.size() && !mParent)
{
mCurrentLod = lodLvl;
mSelfOrChildRendered = true;
mLodTransition = 0;
}
else
{
// check the distance
///------------------------------------------------------------------------
//計算過渡距離distTransition
// Calculate or reuse transition distance
Real distTransition;
LodLevel* ll = *i;
if (Math::RealEqual(cFactor, ll->lastCFactor))
distTransition = ll->lastTransitionDist;
else
{
distTransition = ll->maxHeightDelta * cFactor;
ll->lastCFactor = cFactor;
ll->lastTransitionDist = distTransition;
}
///------------------------------------------------------------------------
//相機(jī)是否離Lod足夠近
//相機(jī)到節(jié)點(diǎn)中心的距離小于過渡距離，則讓其顯示
//對于葉子節(jié)點(diǎn)，Lod0的過渡距離小于Lod1
if (dist < distTransition)
{
// we're within range of this LOD
mCurrentLod = lodLvl;
mSelfOrChildRendered = true;
// Lod在節(jié)點(diǎn)中的存儲順序是用最高細(xì)節(jié)Lod到最低細(xì)節(jié)Lod的順序
// 碰到第一個Lod就結(jié)束了，因為這個Lod細(xì)節(jié)已經(jīng)是最高了
// 一般是葉子的第一個Lod，也即Lod0
break;
}//~相機(jī)足夠近
}
}//~foreach LodLevelList
1.8.4 LOD第二類計算過程
//跳過自身的渲染；we should not render ourself
mCurrentLod = -1;
//當(dāng)前子樹需要被渲染
mSelfOrChildRendered = true;
//只考慮需要渲染的子節(jié)點(diǎn)小于4的情形
if (childRenderedCount < 4)
{
// only *some* children decided to render on their own, but either
// none or all need to render, so set the others manually to their lowest
for (int i = 0; i < 4; ++i)
{
TerrainQuadTreeNode* child = mChildren[i];
if (!child->isSelfOrChildRenderedAtCurrentLod())
{
child->setCurrentLod(child->getLodCount()-1);
child->setLodTransition(1.0);
}
}
} // (childRenderedCount < 4)
第二類計算步驟比較簡單，當(dāng)前節(jié)點(diǎn)有子節(jié)點(diǎn)參與渲染，那自身就不需要參與渲染了。首先標(biāo)記下這個子樹需要被渲染，然后考察其遞歸子節(jié)點(diǎn)需要被渲染的數(shù)量，如果數(shù)量在[1,3]這個區(qū)間，則需要處理這個節(jié)點(diǎn)的4個直接子節(jié)點(diǎn)。
需要處理當(dāng)前節(jié)點(diǎn)的4個直接子節(jié)點(diǎn)的了，如果這個子節(jié)點(diǎn)包含自身的樹都不需要渲染，則將這個節(jié)點(diǎn)的Lod數(shù)量-1。之前在預(yù)計算全局基礎(chǔ)數(shù)據(jù)時已經(jīng)知道，就當(dāng)前這個實(shí)例而言，葉子節(jié)點(diǎn)的Lod數(shù)量是2，非葉子節(jié)點(diǎn)的Lod數(shù)量是0。這樣，對于當(dāng)前節(jié)點(diǎn)的4個子樹，如果這個子樹不參與渲染，則其當(dāng)前Lod=0。
1.9 渲染
地形四叉樹的渲染使用了2個小技巧。一是每個樹節(jié)點(diǎn)Hook了一個內(nèi)嵌類TerrainQuadTreeNode.Rend和Movable參與到場景的管理，而它們并不是一個真實(shí)的場景對象和渲染對象，可以將它們理解為很多人喜歡使用的虛擬對象，在真正需要渲染的時候，將邏輯還是傳遞給TerrainQuadTreeNode。二是地形監(jiān)聽了場景管理器預(yù)渲染方法，這個方法正好在場景管理器八叉樹遍歷場景對象前執(zhí)行。好處顯而易見：讓復(fù)雜的程序結(jié)構(gòu)清晰易讀。
首先，地形四叉樹只應(yīng)用于到地形，而不干涉場景。地形在渲染方面主要做了三件事，一是構(gòu)建了一個四叉樹和對應(yīng)的Lod；二是構(gòu)建了與每個Lod關(guān)聯(lián)的頂點(diǎn)數(shù)據(jù)；三是每個四叉樹節(jié)點(diǎn)都構(gòu)造一個影子render對象和movable對象。
影子moveable對象在地形初次load的時候構(gòu)建完成，每個四叉樹節(jié)點(diǎn)都會新建一個場景節(jié)點(diǎn)，并關(guān)節(jié)上這個引子movable對象，這樣讓每個地形四叉樹節(jié)點(diǎn)參與到場景八叉樹節(jié)點(diǎn)的可見性計算中(當(dāng)前考慮的場景管理器是默認(rèn)的八叉樹場景管理器)。
而在最開始，地形對象監(jiān)聽了場景管理器的SceneManager.firePreFindVisibleObjects方法,而這個方法正好僅僅在計算場景可見渲染對象的前一步:
Class Terrain : public SceneManager::Listener
void SceneManager::_renderScene(Camera* camera, Viewport* vp,
bool includeOverlays)
{
firePreFindVisibleObjects(vp);
findVisibleObjects(camera);
firePostFindVisibleObjects(vp);
// Begin the frame
mDestRenderSystem->_beginFrame();
// Set rasterisation mode
mDestRenderSystem->_setPolygonMode(camera->getPolygonMode());
// Set initial camera state
mDestRenderSystem->_setProjectionMatrix(mCameraInProgress->getProjectionMatrixRS());
// Render scene content
renderVisibleObjects();
// End frame
mDestRenderSystem->_endFrame();
......
于是在渲染場景的時候，每個地形的四叉樹節(jié)點(diǎn)由2個緊鄰的分計算完成。首先預(yù)計算地形Lod，然后的計算其實(shí)是一個通用的場景管理器計算過程，地形并未與場景中其他節(jié)點(diǎn)有所不同。
OgreTerrain_d.dll!Ogre::TerrainQuadTreeNode::calculateCurrentLod
OgreTerrain_d.dll!Ogre::Terrain::calculateCurrentLod
OgreTerrain_d.dll!Ogre::Terrain::preFindVisibleObjects
OgreMain_d.dll!Ogre::SceneManager::firePreFindVisibleObjects
OgreMain_d.dll!Ogre::SceneManager::_renderScene
OgreMain_d.dll!Ogre::Camera::_renderScene
OgreMain_d.dll!Ogre::Viewport::update
OgreMain_d.dll!Ogre::RenderTarget::_updateViewport
RenderSystem_Direct3D9_d.dll!Ogre::D3D9RenderWindow::_updateViewport
OgreMain_d.dll!Ogre::RenderTarget::_updateAutoUpdatedViewports
OgreMain_d.dll!Ogre::RenderTarget::updateImpl
OgreMain_d.dll!Ogre::RenderTarget::update
OgreMain_d.dll!Ogre::RenderSystem::_updateAllRenderTargets
OgreMain_d.dll!Ogre::Root::_updateAllRenderTargets
OgreMain_d.dll!Ogre::Root::renderOneFrame
(地形預(yù)計算Lod )
OgreMain_d.dll!Ogre::RenderQueue::addRenderable
OgreTerrain_d.dll!Ogre::TerrainQuadTreeNode::updateRenderQueue
OgreTerrain_d.dll!Ogre::TerrainQuadTreeNode::Movable::_updateRenderQueue
OgreMain_d.dll!Ogre::RenderQueue::processVisibleObject
Plugin_OctreeSceneManager_d.dll!Ogre::OctreeNode::_addToRenderQueue
Plugin_OctreeSceneManager_d.dll!Ogre::OctreeSceneManager::walkOctree
Plugin_OctreeSceneManager_d.dll!Ogre::OctreeSceneManager::walkOctree
Plugin_OctreeSceneManager_d.dll!Ogre::OctreeSceneManager::walkOctree
Plugin_OctreeSceneManager_d.dll!Ogre::OctreeSceneManager::walkOctree
Plugin_OctreeSceneManager_d.dll!Ogre::OctreeSceneManager::_findVisibleObjects
OgreMain_d.dll!Ogre::SceneManager::_renderScene
OgreMain_d.dll!Ogre::Camera::_renderScene
OgreMain_d.dll!Ogre::Viewport::update
OgreMain_d.dll!Ogre::RenderTarget::_updateViewport
RenderSystem_Direct3D9_d.dll!Ogre::D3D9RenderWindow::_updateViewport
OgreMain_d.dll!Ogre::RenderTarget::_updateAutoUpdatedViewports
OgreMain_d.dll!Ogre::RenderTarget::updateImpl
OgreMain_d.dll!Ogre::RenderTarget::update
OgreMain_d.dll!Ogre::RenderSystem::_updateAllRenderTargets
OgreMain_d.dll!Ogre::Root::_updateAllRenderTargets
OgreMain_d.dll!Ogre::Root::renderOneFrame
(場景管理器通用渲染過程)
實(shí)際計算場景中的可見對象時，如果當(dāng)前地形四叉樹的影子Movable對象在相機(jī)中可見，那么只要這個四叉樹節(jié)點(diǎn)中的當(dāng)前Lod不是-1，就將其加入到渲染隊列。還記得當(dāng)前Lod表示的時候這個四叉樹節(jié)點(diǎn)LodLevel層級中需要被渲染的那個Lod，這樣在這里，這個渲染對象還是間接的渲染的一個LodLevel，這個真實(shí)的渲染對象在于場景管理器打交道的時候，表現(xiàn)為它的影子渲染對象TerrainQuadTreeNode.Rend。
如此這般，場景中需要渲染的對象都組裝好了，好好的躺在渲染隊列中。萬事俱備只欠東風(fēng)，是時候渲染了，這個渲染方法SceneManager.renderVisibleObjects在場景對象的預(yù)計算、實(shí)際計算兩個步驟之后。
OgreTerrain_d.dll!Ogre::TerrainQuadTreeNode::getRenderOperation
OgreTerrain_d.dll!Ogre::TerrainQuadTreeNode::Rend::getRenderOperation
OgreMain_d.dll!Ogre::SceneManager::renderSingleObject
OgreMain_d.dll!Ogre::SceneManager::SceneMgrQueuedRenderableVisitor::visit
OgreMain_d.dll!Ogre::QueuedRenderableCollection::acceptVisitorGrouped
OgreMain_d.dll!Ogre::QueuedRenderableCollection::acceptVisitor
OgreMain_d.dll!Ogre::SceneManager::renderObjects
OgreMain_d.dll!Ogre::SceneManager::renderBasicQueueGroupObjects
OgreMain_d.dll!Ogre::SceneManager::_renderQueueGroupObjects
OgreMain_d.dll!Ogre::SceneManager::renderVisibleObjectsDefaultSequence
OgreMain_d.dll!Ogre::SceneManager::_renderVisibleObjects
OgreMain_d.dll!Ogre::SceneManager::_renderScene
OgreMain_d.dll!Ogre::Camera::_renderScene
OgreMain_d.dll!Ogre::Viewport::update
OgreMain_d.dll!Ogre::RenderTarget::_updateViewport
RenderSystem_Direct3D9_d.dll!Ogre::D3D9RenderWindow::_updateViewport
OgreMain_d.dll!Ogre::RenderTarget::_updateAutoUpdatedViewports
OgreMain_d.dll!Ogre::RenderTarget::updateImpl
OgreMain_d.dll!Ogre::RenderTarget::update
OgreMain_d.dll!Ogre::RenderSystem::_updateAllRenderTargets
OgreMain_d.dll!Ogre::Root::_updateAllRenderTargets
OgreMain_d.dll!Ogre::Root::renderOneFrame
//渲染數(shù)據(jù)
void TerrainQuadTreeNode::getRenderOperation(RenderOperation& op)
{
mNodeWithVertexData->updateGpuVertexData();
op.indexData = mLodLevels[mCurrentLod]->gpuIndexData;
op.operationType = RenderOperation::OT_TRIANGLE_STRIP;
op.useIndexes = true;
op.vertexData = getVertexDataRecord()->gpuVertexData;
}
之前說過，加入到渲染隊列的是影子渲染對象，真實(shí)渲染對象是一個LodLevel，這是一個很好的橋接模式，避免了地形四叉樹場景八叉樹之間的耦合。其實(shí)實(shí)現(xiàn)原理也非常簡單，不能直接交互的2個對象之間需要交互，就讓可以變通的對象投其所好，構(gòu)建一個讓另外那個對象熟悉的影子對象給它使用，只是在這個引子對象被訪問的時候，將訪問權(quán)限還是還給它的“真身”。
這樣在渲染具體的LodLevel的時候，立即通過當(dāng)前Lod標(biāo)記找到這個具體的LodLevel，裝配好需要的數(shù)據(jù)交給GPU完成圖形設(shè)備的渲染流程。