#include <osg/Geometry>
#include <osg/Geode>
#include <osg/Program>
#include <osg/VertexAttribDivisor>
#include <osgViewer/Viewer>
#include <osgViewer/ViewerEventHandlers>
#include <random>
// 创建单个立方体几何体（共享基础形状）
osg::ref_ptr<osg::Geometry> createCubeGeometry(int vtx) {
    osg::ref_ptr<osg::Geometry> geom = new osg::Geometry;

    // 立方体8个顶点（单位立方体，中心在原点）
    osg::Vec3Array* vertices = new osg::Vec3Array;
    vertices->push_back(osg::Vec3(-0.5, -0.5, -0.5)); // 0 左前下
    vertices->push_back(osg::Vec3(0.5, -0.5, -0.5)); // 1 右前下
    vertices->push_back(osg::Vec3(0.5, 0.5, -0.5)); // 2 右后下
    vertices->push_back(osg::Vec3(-0.5, 0.5, -0.5)); // 3 左后下
    vertices->push_back(osg::Vec3(-0.5, -0.5, 0.5)); // 4 左前上
    vertices->push_back(osg::Vec3(0.5, -0.5, 0.5)); // 5 右前上
    vertices->push_back(osg::Vec3(0.5, 0.5, 0.5)); // 6 右后上
    vertices->push_back(osg::Vec3(-0.5, 0.5, 0.5)); // 7 左后上
    geom->setVertexArray(vertices);

    // 立方体6个面的法线（用于光照计算）
    osg::Vec3Array* normals = new osg::Vec3Array;
    normals->push_back(osg::Vec3(0, 0, -1)); // 前面
    normals->push_back(osg::Vec3(0, 0, 1)); // 后面
    normals->push_back(osg::Vec3(-1, 0, 0)); // 左面
    normals->push_back(osg::Vec3(1, 0, 0)); // 右面
    normals->push_back(osg::Vec3(0, -1, 0)); // 底面
    normals->push_back(osg::Vec3(0, 1, 0)); // 顶面
    geom->setNormalArray(normals, osg::Array::BIND_PER_PRIMITIVE_SET);

    std::vector<GLuint> idxbuffer;

    // 前面
    idxbuffer.push_back(0); idxbuffer.push_back(1); idxbuffer.push_back(2);
    idxbuffer.push_back(2); idxbuffer.push_back(3); idxbuffer.push_back(0);
    // 后面
    idxbuffer.push_back(4); idxbuffer.push_back(7); idxbuffer.push_back(6);
    idxbuffer.push_back(6); idxbuffer.push_back(5); idxbuffer.push_back(4);
    // 左面
    idxbuffer.push_back(0); idxbuffer.push_back(3); idxbuffer.push_back(7);
    idxbuffer.push_back(7); idxbuffer.push_back(4); idxbuffer.push_back(0);
    // 右面
    idxbuffer.push_back(1); idxbuffer.push_back(5); idxbuffer.push_back(6);
    idxbuffer.push_back(6); idxbuffer.push_back(2); idxbuffer.push_back(1);
    // 底面
    idxbuffer.push_back(0); idxbuffer.push_back(4); idxbuffer.push_back(5);
    idxbuffer.push_back(5); idxbuffer.push_back(1); idxbuffer.push_back(0);
    // 顶面
    idxbuffer.push_back(3); idxbuffer.push_back(2); idxbuffer.push_back(6);
    idxbuffer.push_back(6); idxbuffer.push_back(7); idxbuffer.push_back(3);

    // 定义12个三角形（每个面2个三角形）
    osg::DrawElementsUInt* indices = new osg::DrawElementsUInt(GL_TRIANGLES, 36, idxbuffer.data(), vtx);

    geom->addPrimitiveSet(indices);

    geom->setUseDisplayList(false);
    geom->setUseVertexBufferObjects(true);
    return geom;
}

// 创建实例化变换矩阵数组
osg::ref_ptr<osg::Vec3Array> createInstancePositions(int count) {
    osg::ref_ptr<osg::Vec3Array> positions = new osg::Vec3Array;
    std::random_device rd;
    std::mt19937 gen(rd());
    const auto len = sqrt(count);
    std::uniform_real_distribution<float> dis(-len, len);

    for (int i = 0; i < count; ++i) {
        positions->push_back(osg::Vec3(dis(gen), dis(gen), dis(gen)));
    }
    return positions;
}
///gl_InstanceID
const std::string  vertex_shader = R"(
                    #version 430 compatibility
                    layout(location = 0) in vec3 vertexPosition;
                    layout(location = 6) in vec3 instancePosition;
                    uniform mat4 osg_ModelViewProjectionMatrix;
                    void main() {
                        vec4 pos = vec4(vertexPosition + instancePosition, 1.0);
                        gl_Position =  gl_ModelViewProjectionMatrix * pos;
                    }
)";
const std::string  frag_shader = R"(
                    #version 430 core
                    out vec4 fragColor;
                    void main() {
                        fragColor = vec4(0.8, 0.3, 0.2, 1.0); 
                    }
)";
int main() {
    // 创建场景根节点
    osg::ref_ptr<osg::Group> root = new osg::Group;

    constexpr int instanceCount = 100; // 实例数量

    // 创建共享几何体
    osg::ref_ptr<osg::Geometry> cube = createCubeGeometry(instanceCount);

    // 设置实例化属性（位置）
    osg::ref_ptr<osg::Vec3Array> instancePositions = createInstancePositions(instanceCount);

    instancePositions->setBinding(osg::Array::Binding::BIND_PER_VERTEX);
    cube->setVertexAttribArray(6, instancePositions); // 绑定到属性索引6

    cube->getOrCreateStateSet()->setAttribute(new osg::VertexAttribDivisor(6, 1));//(顶点属性索引,*实例使用相同的顶点属)

    // 创建几何节点并添加到场景
    osg::ref_ptr<osg::Geode> geode = new osg::Geode;
    geode->addDrawable(cube);
    root->addChild(geode);

    // 配置实例化着色器
    osg::ref_ptr<osg::Program> program = new osg::Program;

    program->addShader(new osg::Shader(osg::Shader::VERTEX, vertex_shader.c_str()));
    program->addShader(new osg::Shader(osg::Shader::FRAGMENT, frag_shader.c_str()));
    geode->getOrCreateStateSet()->setAttribute(program);
    
    // 启动查看器
    osgViewer::Viewer viewer;
    viewer.setUpViewInWindow(100, 100, 800, 600);
    viewer.setSceneData(root);
    viewer.addEventHandler(new osgViewer::StatsHandler());
    viewer.getCamera()->setNearFarRatio(1e-5);
    viewer.getCamera()->setProjectionMatrixAsPerspective(60, 800 / (float)600, 1, 100);
    viewer.getCamera()->setComputeNearFarMode(osg::CullSettings::DO_NOT_COMPUTE_NEAR_FAR);
    return viewer.run();
}