osg绘制立体几何

根据网友的代码，实现了，然后自己画出来立方体什么的，发现并不难。。。加入顶点坐标然后根据坐标数组进行绘制

一、openGL中，定义了10种图元：GL_POINTS, GL_LINES, GL_LINE_STRIP, GL_LINE_LOOP, GL_TRIANGLES, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN, GL_QUADS, GL_QUAD_STRIP, GL_POLYGON

十种图元的作用比较简单，就不多介绍。

二、OSG中图元的设置是通过

bool addPrimitiveSet(PrimitiveSet* primitiveset);

所有图元类都继承于PrimitiveSet，不同的图元类可以以不同的方式解释顶点数组（不仅仅是OpenGL的那些方式）

四、osg::DrawArrays

五、osg::DrawElementsUInt

此类依赖两个东西解释顶点数组，第一个当然是顶点数组了，第二个是个索引数组。索引数组是什么呢？举个例子。

有如下两个三角形（ABC)(BCD)，如果想以GL_TRIANGLES方式绘制，如果用DrawArrays，就要往顶点数组中插6个顶点ABCBCD，如果三角面巨多，有这么多重复顶点是不可接受的。而使用osg::DrawElementsUInt可以解决此问题。

DrawElementsUInt接受一个索引数组IndexArray，是对顶点数组的索引，如此顶点数组中就可以只放ABCD四个顶点，而索引数组为(123234)6个数字，这样存储代价就小了许多。

DrawElemetnsUInt(osg::PrimitiveSet::TRIANGLES, IndexArray->size(), &IndexArray->front())

#include <Windows.h>
#include <osgViewer/Viewer>
#include <osg/Group>
#include <osgDB/ReadFile>

int main(void)
{
osg::ref_ptrosgViewer::Viewer viewer = new osgViewer::Viewer;

osg::ref_ptr<osg::Group> sceneRoot = new osg::Group;

//创建几何体
osg::ref_ptr<osg::Geometry> geometry = new osg::Geometry;
osg::Vec4dArray* color = new osg::Vec4dArray;
color->push_back(osg::Vec4d(0.0, 0.0, 1.0, 1.0));
geometry->setColorArray(color);
osg::Vec3Array* vecArray = new osg::Vec3Array;
vecArray->push_back(osg::Vec3d(0.0,0.0,0.0));
vecArray->push_back(osg::Vec3d(4.0,0.0,0.0));
vecArray->push_back(osg::Vec3d(2.0, 4.0, 0.0));
vecArray->push_back(osg::Vec3d(2.0, 2.0, 4.0));
geometry->setVertexArray(vecArray);

osg::ref_ptr<osg::DrawElementsUInt> drawElemUInt = new osg::DrawElementsUInt(GL_TRIANGLE_FAN);
drawElemUInt->push_back(0);
drawElemUInt->push_back(1);
drawElemUInt->push_back(1);
drawElemUInt->push_back(2);
drawElemUInt->push_back(2);
drawElemUInt->push_back(0);

drawElemUInt->push_back(0);
drawElemUInt->push_back(1);
drawElemUInt->push_back(1);
drawElemUInt->push_back(3);
drawElemUInt->push_back(3);
drawElemUInt->push_back(0);

drawElemUInt->push_back(0);
drawElemUInt->push_back(2);
drawElemUInt->push_back(2);
drawElemUInt->push_back(3);
drawElemUInt->push_back(3);
drawElemUInt->push_back(0);


drawElemUInt->push_back(1);
drawElemUInt->push_back(3);
drawElemUInt->push_back(3);
drawElemUInt->push_back(2);
drawElemUInt->push_back(2);
drawElemUInt->push_back(1);

geometry->addPrimitiveSet(drawElemUInt);
osg::Geode* geode = new osg::Geode;
geode->addDrawable(geometry);

sceneRoot->addChild(geode);

viewer->setSceneData(sceneRoot);
viewer->realize();
return viewer->run();

}