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OpenSceneGraph (OSG) 开发入门

news 来源：原创 2025/6/22 23:13:45

一、环境搭建

1. 安装OSG

Windows

下载预编译包：从OSG官方网站下载
设置环境变量：
- 添加OSG_ROOT指向安装目录
- 将%OSG_ROOT%\bin添加到PATH

Linux (Ubuntu)

sudo apt-get install openscenegraph libopenscenegraph-dev openscenegraph-examples

macOS (使用Homebrew)

brew install open-scene-graph

2. 验证安装

osgversion  # 查看版本
osgviewer cow.osgt  # 测试示例模型

二、第一个OSG程序

1. 基本程序结构

#include <osgViewer/Viewer>
#include <osgDB/ReadFile>

int main() {
    // 创建Viewer
    osgViewer::Viewer viewer;
    
    // 加载模型
    osg::Node* node = osgDB::readNodeFile("cow.osgt");
    
    // 设置场景数据
    viewer.setSceneData(node);
    
    // 运行查看器
    return viewer.run();
}

2. 编译命令

Linux/macOS

g++ hello_osg.cpp -losgViewer -losgDB -o hello_osg

Windows (Visual Studio)

新建C++项目
配置包含目录：$(OSG_ROOT)\include
配置库目录：$(OSG_ROOT)\lib
添加依赖库：osgViewer.lib;osgDB.lib;OpenThreads.lib

三、核心概念

1. 场景图结构

场景根(Group)
├─ 变换节点(MatrixTransform)
│  └─ 几何节点(Geode)
│     └─ 几何体(Geometry)
└─ 细节层次节点(LOD)
   ├─ 高细节模型
   └─ 低细节模型

2. 基本组件

组件	说明
`osg::Node`	场景图中所有节点的基类
`osg::Group`	可包含子节点的组节点
`osg::Geode`	几何体节点(叶子节点)
`osg::Geometry`	存储几何数据(顶点、法线等)
`osgViewer::Viewer`	3D场景查看器

四、创建自定义场景

1. 创建简单几何体

osg::Geode* createQuad() {
    osg::ref_ptr<osg::Geode> geode = new osg::Geode;
    osg::ref_ptr<osg::Geometry> geom = new osg::Geometry;
    
    // 设置顶点
    osg::Vec3Array* vertices = new osg::Vec3Array;
    vertices->push_back(osg::Vec3(-1,0,-1));
    vertices->push_back(osg::Vec3(1,0,-1));
    vertices->push_back(osg::Vec3(1,0,1));
    vertices->push_back(osg::Vec3(-1,0,1));
    geom->setVertexArray(vertices);
    
    // 设置颜色
    osg::Vec4Array* colors = new osg::Vec4Array;
    colors->push_back(osg::Vec4(1,0,0,1)); // 红
    colors->push_back(osg::Vec4(0,1,0,1)); // 绿
    colors->push_back(osg::Vec4(0,0,1,1)); // 蓝
    colors->push_back(osg::Vec4(1,1,0,1)); // 黄
    geom->setColorArray(colors);
    geom->setColorBinding(osg::Geometry::BIND_PER_VERTEX);
    
    // 添加图元
    geom->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::QUADS, 0, 4));
    
    geode->addDrawable(geom);
    return geode.release();
}

2. 构建场景图

osg::Group* createScene() {
    osg::ref_ptr<osg::Group> root = new osg::Group;
    
    // 添加多个几何体
    root->addChild(createQuad());
    
    // 添加变换节点
    osg::ref_ptr<osg::MatrixTransform> transform = new osg::MatrixTransform;
    transform->setMatrix(osg::Matrix::translate(2,0,0));
    transform->addChild(createCube());
    root->addChild(transform);
    
    return root.release();
}

五、交互与动画

1. 键盘事件处理

class KeyboardHandler : public osgGA::GUIEventHandler {
public:
    bool handle(const osgGA::GUIEventAdapter& ea, osgGA::GUIActionAdapter& aa) {
        if (ea.getEventType() == osgGA::GUIEventAdapter::KEYDOWN) {
            switch (ea.getKey()) {
                case 'a': 
                    // 处理A键按下
                    return true;
                case osgGA::GUIEventAdapter::KEY_Left:
                    // 处理左箭头
                    return true;
            }
        }
        return false;
    }
};

// 添加到查看器
viewer.addEventHandler(new KeyboardHandler());

2. 简单动画

class AnimationCallback : public osg::NodeCallback {
public:
    void operator()(osg::Node* node, osg::NodeVisitor* nv) {
        osg::MatrixTransform* mt = dynamic_cast<osg::MatrixTransform*>(node);
        if (mt) {
            double time = osg::Timer::instance()->time_s();
            mt->setMatrix(osg::Matrix::translate(0, 0, sin(time)*2));
        }
        traverse(node, nv);
    }
};

// 应用到变换节点
transform->setUpdateCallback(new AnimationCallback());

六、进阶主题

1. 着色器编程

osg::StateSet* addShader(osg::Node* node) {
    osg::ref_ptr<osg::Program> program = new osg::Program;
    program->addShader(osgDB::readShaderFile(osg::Shader::VERTEX, "shader.vert"));
    program->addShader(osgDB::readShaderFile(osg::Shader::FRAGMENT, "shader.frag"));
    
    osg::StateSet* stateset = node->getOrCreateStateSet();
    stateset->setAttributeAndModes(program, osg::StateAttribute::ON);
    
    return stateset;
}

2. 粒子系统

osg::Node* createFireEffect() {
    osgParticle::ParticleSystem* ps = new osgParticle::ParticleSystem;
    // 配置粒子系统...
    
    osgParticle::ModularEmitter* emitter = new osgParticle::ModularEmitter;
    emitter->setParticleSystem(ps);
    // 配置发射器...
    
    osg::Group* root = new osg::Group;
    root->addChild(emitter);
    root->addChild(new osgParticle::ParticleSystemUpdater(ps));
    
    return root;
}