osg自动生成法线的方法

所谓的法线是指 物品在光的照射下肉眼能看到的物体的面 而物体里面是看不到的。也就说，计算光照是运算需要法线。未设置法线那么一般情况是看不到物体的，处于一片漆黑状态。

注意自动算法向量要求是添加顶点顺序是逆时针

#include<osgDB/ReadFile>#include<osgViewer/Viewer>#include<osg/Node>#include<osg/Geode>#include<osg/Geometry>#include <osgUtil/SmoothingVisitor>osg::ref_ptr<osg::Node> createQuad();void main(){    osgViewer::Viewer viewer;    osg::Group *root=new osg::Group();    root->addChild(createQuad().get());    viewer.setSceneData(root);    viewer.realize();    viewer.run();}osg::ref_ptr<osg::Node> createQuad(){    osg::ref_ptr<osg::Geometry> geom=new osg::Geometry;    //首先定义四个点    osg::ref_ptr<osg::Vec3Array> v=new osg::Vec3Array;    geom->setVertexArray(v.get());    v->push_back(osg::Vec3(-1.f,0.f,-1.f));    v->push_back(osg::Vec3(1.f,0.f,-1.f));    v->push_back(osg::Vec3(1.f,0.f,1.f));    v->push_back(osg::Vec3(-1.f,0.f,1.f));    //定义颜色数组    osg::ref_ptr<osg::Vec4Array> c=new osg::Vec4Array;    geom->setColorArray(c.get());    geom->setColorBinding(osg::Geometry::BIND_PER_VERTEX);    c->push_back(osg::Vec4(1.f,0.f,0.f,1.f));    c->push_back(osg::Vec4(0.f,1.f,0.f,1.f));    c->push_back(osg::Vec4(0.f,0.f,1.f,1.f));    c->push_back(osg::Vec4(1.f,1.f,1.f,1.f));    //设置定点关联方式    geom->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::QUADS,0,4));    //方法一    //手动定义法线    osg::ref_ptr<osg::Vec3Array> n=new osg::Vec3Array;    geom->setNormalArray(n.get());    geom->setNormalBinding(osg::Geometry::BIND_OVERALL);    n->push_back(osg::Vec3(-2.f,-1.f,10.f));    //方法二    //自动生成法线

//注意这里自动生成法向量是按逆时针即右手定则类似    //osgUtil::SmoothingVisitor::smooth(*(geom.get()));//自动生成法线    osg::ref_ptr<osg::Geode> geode=new osg::Geode;    geode->addDrawable(geom.get());    return geode.get();}