PagedGeometry笔记

PagedGeometry版本：1.1

ONE.静态树
a).创建PagedGeometry对象，用于管理草体的细节
PagedGeometry *trees = new PagedGeometry();

1    trees->setCamera(camera);    //Set the camera so PagedGeometry knows how to calculate LODs
2    trees->setPageSize(80);    //Set the size of each page of geometry
3    trees->setInfinite();        //Use infinite paging mode
4    trees->addDetailLevel<BatchPage>(150, 50);        //Use batches up to 150 units away, and fade for 30 more units
5    trees->addDetailLevel<ImpostorPage>(500, 50);    //Use impostors up to 400 units, and for for 50 more units

b).创建草体加载器，用于加载加载草体，铺草
TreeLoader3D *treeLoader = new TreeLoader3D(trees, TBounds(0, 0, 1500,1500));

 1    trees->setPageLoader(treeLoader);    //Assign the "treeLoader" to be used to load geometry for the PagedGeometry instance
 2
 3    //Load a tree entity
 4    Entity *myEntity = sceneMgr->createEntity("Tree", "tree2.mesh");
 5
 6    //Setup the height function (so the Y values of trees can be calculated when they are placed on the terrain)
 7    HeightFunction::initialize(sceneMgr);
 8
 9    //Randomly place 20,000 copies of the tree on the terrain
10    Vector3 position;
11    Radian yaw;
12    Real scale;
13    for (int i = 0; i < 20000; i++){
14        yaw = Degree(Math::RangeRandom(0, 360));
15
16        position.x = Math::RangeRandom(0, 1500);
17        position.z = Math::RangeRandom(0, 1500);
18        position.y = HeightFunction::getTerrainHeight(position.x, position.z);
19
20        scale = Math::RangeRandom(0.5f, 0.6f);
21
22        treeLoader->addTree(myEntity, position, yaw, scale);
23    }

c).帧循环中进行更新

trees->update();

其内部有3个动作：
1.更新loader
2.更新内部对象：GeometryPageManager
3. Update misc. subsystems

StaticBillboardSet::updateAll(_convertToLocal(getCamera()->getDerivedDirection()));

d).退出时清理内存

 1    //[NOTE] Always remember to delete any PageLoader(s) and PagedGeometry instances in order to avoid memory leaks.
 2
 3    //Delete the TreeLoader3D instance
 4    delete trees->getPageLoader();
 5
 6    //Delete the PagedGeometry instance
 7    delete trees;
 8
 9    //Also delete the tree entity
10    sceneMgr->destroyEntity("Tree");

---

TWO.动态草体

动态草和静态树的创建如出一辙，只是将植物加载器换从“TreeLoader3D”换成了“GrassLoader”而已，顺利成章的，如果要家长其他不同类的植物，只需使用一个该植物的“XXXLoader”即可。其实整个PagedGeometry中的加载器只有三个，PageLoader派生了3个加载器：
 - Forests::GrassLoader
 - Forests::TreeLoader2D
 - Forests::TreeLoader3D

GrassLoader创建如下：

1    grassLoader = new GrassLoader(grass);
2    grass->setPageLoader(grassLoader);    //Assign the "treeLoader" to be used to load geometry for the PagedGeometry instance
3
4    //Supply a height function to GrassLoader so it can calculate grass Y values
5    HeightFunction::initialize(sceneMgr);
6    grassLoader->setHeightFunction(&HeightFunction::getTerrainHeight);

GrassLoader借助一个GrassLayer对象来“植树”：

 1    //Add some grass to the scene with GrassLoader::addLayer()
 2    GrassLayer *l = grassLoader->addLayer("grass");
 3
 4    //Configure the grass layer properties (size, density, animation properties, fade settings, etc.)
 5    l->setMinimumSize(2.0f, 2.0f);
 6    l->setMaximumSize(2.5f, 2.5f);
 7    l->setAnimationEnabled(true);        //Enable animations
 8    l->setSwayDistribution(10.0f);        //Sway fairly unsynchronized
 9    l->setSwayLength(0.5f);                //Sway back and forth 0.5 units in length
10    l->setSwaySpeed(0.5f);                //Sway 1/2 a cycle every second
11    l->setDensity(1.5f);                //Relatively dense grass
12    l->setFadeTechnique(FADETECH_GROW);    //Distant grass should slowly raise out of the ground when coming in range
13    l->setRenderTechnique(GRASSTECH_QUAD);    //Draw grass as scattered quads
14
15    //This sets a color map to be used when determining the color of each grass quad. setMapBounds()
16    //is used to set the area which is affected by the color map. Here, "terrain_texture.jpg" is used
17    //to color the grass to match the terrain under it.
18    l->setColorMap("terrain_texture.jpg");
19    l->setMapBounds(TBounds(0, 0, 1500, 1500));    //(0,0)-(1500,1500) is the full boundaries of the terrain

a).源码中队GrassLayer的说明

A data structure giving you full control over grass properties.Grass is added to the scene through GrassLoader::addLayer(). Through this class you can configure your grass layer any way you like - size, density, render technique,animation, etc. Simply call the appropriate "set" member function to set the desired property.Remember that you cannot create or delete layers directly. Layers can only be created with GrassLoader::addLayer(), and may not be deleted manually (they will be deleted when the associated GrassLoader is deleted).
 - GrassLayer只能通过GrassLoader::addLayer()来创建
 - GrassLoader不能直接创建或删除
 - GrassLoader不能进行手动删除

    addlayer传给GrassLayer的参数是一个字符串，这个字符串是一个material的名字，以便渲染手动创建的草体mesh时使用。

1GrassLayer *GrassLoader::addLayer(const String &material)
2{
3    GrassLayer *layer = new GrassLayer(geom, this);
4    layer->setMaterialName(material);
5    layerList.push_back(layer);
6
7    return layer;
8}

b).草实体的创建
草体是在GrassLoader::loadPage中创建的

                    mesh = generateGrass_QUAD(page, layer, position, grassCount);

而loadPage是在帧循环调用“GeometryPageManager::update”时调用的，通过GeometryPageManager::update的“cacheInterval”技术实现渲染前调用一次，好比在帧循环中设置一个标志位，如果发现草实体没有创建，则创建之。这里的generateGrass_QUAD实现了一个手动创建mesh的方法。

THREE.静态树和动态草一起

创建2个PagedGeometry对象，分别互不干涉的各管各即可。当然需要在帧循环中分别更新了。


FOUR.2D树和3D树的区别

If the inability to supply a vertical coordinate to addTree() is too limiting, or you are unable to implement
a fast enough height function, please refer to TreeLoader3D. TreeLoader3D allows you to provide full 3D x/y/z
coordinates, although 40% more memory is required per tree.
更多说明见<pagedGeometry-1.1.0/include/TreeLoader2D.h>
 - 2D树非常省内存
 - 2D树对放置的3D坐标有限制
 - 3D树可以设置完全的3D坐标
 - 3D树的每一颗树都比2D树多占用40%的内存