osg学习-3《绘制三维曲面》

 演示了创建曲面节点的函数

（1）首先设置面数据的顶点坐标，设置面数据在I和J方向的网格个数，以及网格间距，随便设置z和颜色。也可以通过读取外部数据的方式获取顶点坐标和网格上的属性值，根据需要的色标计算每个网格的rgb颜色值。

（2）每个网格一个图元，设置它的坐标索引，并设置颜色数组，通过图元绑定的方式渲染进行显示。

效果如下，下面是代码。

// osg_hello.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
#include <random>

#ifdef _WIN32
#include <windows.h>
#endif

#include <osgViewer/Viewer>

#include <osg/Node>
#include <osg/Geode>
#include <osg/Group>

#include <osgDB/ReadFile>
#include <osgDB/WriteFile>

#include <osgUtil/Optimizer>


/// <summary>
/// 创建曲面节点对象
/// </summary>
/// <returns></returns>
osg::ref_ptr<osg::Node> createSurface() {
    //创建一个节点对象
    osg::ref_ptr<osg::Geode> geode = new osg::Geode();
    //创建一个集合对象
    osg::ref_ptr<osg::Geometry> geom = new osg::Geometry();

    //面数据网格的相关参数
    int ni = 20;
    int nj = 20;
    float dx = 10.0f;
    float dy = 5.0f;
    float xMid = ni * dx / 2;
    float yMid = nj * dy / 2;

    //创建顶点数组
    osg::ref_ptr<osg::Vec3Array> vertx = new osg::Vec3Array();
    for (int j = 0; j <= nj; j++) {
        float y = j * dy;
        for (int i = 0; i <= ni; i++) {
            float x = i * dx;
            float z = -0.5 * sqrt(pow(x - xMid, 2) + pow(y - yMid, 2));         
            vertx->push_back(osg::Vec3(x,y,z));
        }
    }

    std::random_device dev;
    std::default_random_engine rnd(dev());
    std::uniform_real_distribution<float> u(0,1);

    //设置顶点数据
    geom->setVertexArray(vertx.get());
    //创建颜色数组
    osg::ref_ptr<osg::Vec4Array> vcolor = new osg::Vec4Array();

    for (int j = 0; j < nj; j++) {
        for (int i = 0; i < ni; i++) {
            int index = j * (ni+1) + i;
            //创建四边形定点数组，指定绘图基元为四边形，注意添加顺序
            osg::ref_ptr<osg::DrawElementsUInt> quad =
                new osg::DrawElementsUInt(osg::PrimitiveSet::QUADS, 0);
            quad->push_back(index);
            quad->push_back(index + 1);
            quad->push_back(index + ni + 2);
            quad->push_back(index + ni + 1);
            
            //添加到几何体
            geom->addPrimitiveSet(quad.get());           
            //vcolor->push_back(osg::Vec4(1.0f, 0.0f, 0.0f, 1.0f));  //red
            vcolor->push_back(osg::Vec4(u(rnd), u(rnd), u(rnd), 1.0f));  //random color for simple
        }
    }

    //设置颜色数组
    geom->setColorArray(vcolor.get());


    //设置颜色的绑定方式为单个顶点
    //geom->setColorBinding(osg::Geometry::BIND_PER_VERTEX);
    geom->setColorBinding(osg::Geometry::BIND_PER_PRIMITIVE_SET);

    // 创建法线数组
    osg::ref_ptr<osg::Vec3Array>nc = new osg::Vec3Array();
    //添加法线
    nc->push_back(osg::Vec3(0.0f, -1.0f, 0.0f));

    // 设置法线数组
    geom->setNormalArray(nc.get());
    //设置法线的绑定方式为全部顶点
    geom->setNormalBinding(osg::Geometry::BIND_OVERALL);

    //添加到叶节点
    geode->addDrawable(geom.get());

    return geode.get();
}

int main()
{
    // 创建Viewer对象，场景浏览器创建一个节点。viewer->setSceneData(root.get())viewer->realize(viewer - un(）;
    osg::ref_ptr<osgViewer::Viewer> viewer = new osgViewer::Viewer();

    //创建场最组节点
    osg::ref_ptr<osg::Group> root = new osg::Group();

    //创建面对象
    osg::ref_ptr<osg::Node> node = createSurface();

    //添加到场景
    root->addChild(node.get());

    //优化场景数据
    osgUtil::Optimizer optimizer;
    optimizer.optimize(root.get());

    //设置场景数据
    viewer->setSceneData(root.get());

    //设置渲染的窗口
    //viewer->setUpViewAcrossAllScreens();  //default on all screens
    viewer->setUpViewOnSingleScreen(0);

    //开始渣染
    viewer->run();

    return 0;
}