使用“告示板”

osg中有一种结点叫做告示板结点，其从osg::Geode类派生，它与其他的osg::Geode类相似，但它有一个特点就是能够让自己的一面朝向观察屏幕。这样就可以有很多的应用，比如说，可以用多个这种结点做成一片森林。

osg::Billboard类有两种朝向方式，一种是平行于观察平面，一种是垂直与观察点。

#include <osg/Image>#include <osg/Geometry>#include <osg/Billboard>#include <osg/StateSet>#include <osg/Group>#include <osg/Texture2D>#include <osg/PositionAttitudeTransform>#include <osgDB/readfile>#include <osgViewer/Viewer>#include <iostream>#ifdef _DEBUG#pragma comment(lib,"osgd.lib")#pragma comment(lib,"osgDBd.lib")#pragma comment(lib,"osgViewerd.lib")#else#pragma comment(lib,"osg.lib")#pragma comment(lib,"osgDB.lib")#pragma comment(lib,"osgViewer.lib")#endif//生成一个矩形osg::ref_ptr<osg::Geometry> createTree(){//绘制四边形osg::ref_ptr<osg::Geometry> rect = new osg::Geometry;//顶点坐标osg::ref_ptr<osg::Vec3Array> vectexArray = new osg::Vec3Array;vectexArray->push_back(osg::Vec3(-0.5f,0.0f,-0.5f));vectexArray->push_back(osg::Vec3(0.5f,0.0f,-0.5f));vectexArray->push_back(osg::Vec3(0.5f,0.0f,0.5f));vectexArray->push_back(osg::Vec3(-0.5f,0.0f,0.5f));rect->setVertexArray(vectexArray.get());//法向osg::ref_ptr<osg::Vec3Array> normalArray = new osg::Vec3Array;normalArray->push_back(osg::Vec3(1.0f,0.0f,0.0f)^osg::Vec3(0.0f,0.0f,1.0f));rect->setNormalArray(normalArray.get());rect->setNormalBinding(osg::Geometry::BIND_OVERALL);//纹理映射osg::ref_ptr<osg::Vec2Array> coordArray = new osg::Vec2Array;coordArray->push_back(osg::Vec2(0.0f,0.0f));coordArray->push_back(osg::Vec2(1.0f,0.0f));coordArray->push_back(osg::Vec2(1.0f,1.0f));coordArray->push_back(osg::Vec2(0.0f,1.0f));rect->setTexCoordArray(0,coordArray.get());rect->addPrimitiveSet(new osg::DrawArrays(GL_QUADS,0,4));return rect;}int main(int args,char** argv){osg::ref_ptr<osg::Group> root = new osg::Group;osg::ref_ptr<osg::Image> treeImage = osgDB::readImageFile("Images/tree0.rgba");//定义三种不同的告示板结点osg::ref_ptr<osg::Billboard> treeBillboard_rot_world = new osg::Billboard;treeBillboard_rot_world->setMode(osg::Billboard::POINT_ROT_WORLD);treeBillboard_rot_world->addDrawable(createTree().get());osg::ref_ptr<osg::Billboard> treeBillboard_rot_eye = new osg::Billboard;treeBillboard_rot_eye->setMode(osg::Billboard::POINT_ROT_EYE);treeBillboard_rot_eye->addDrawable(createTree().get());osg::ref_ptr<osg::Billboard> treeBillboard_rot_axial = new osg::Billboard;treeBillboard_rot_axial->setMode(osg::Billboard::AXIAL_ROT);treeBillboard_rot_axial->addDrawable(createTree().get());//普通结点osg::ref_ptr<osg::Geode> tree = new osg::Geode;tree->addDrawable(createTree().get());//分别贴上大树纹理if (treeImage.get()){osg::ref_ptr<osg::Texture2D> treeTexture = new osg::Texture2D;treeTexture->setDataVariance(osg::Object::DYNAMIC);treeTexture->setImage(treeImage.get());osg::ref_ptr<osg::StateSet> treeStateSet = new osg::StateSet;treeStateSet->setTextureAttributeAndModes(0,treeTexture.get());treeStateSet->setMode(GL_LIGHTING,osg::StateAttribute::OFF);treeStateSet->setMode(GL_BLEND,osg::StateAttribute::ON);treeBillboard_rot_world->setStateSet(treeStateSet.get());treeBillboard_rot_eye->setStateSet(treeStateSet.get());treeBillboard_rot_axial->setStateSet(treeStateSet.get());tree->setStateSet(treeStateSet.get());}treeBillboard_rot_eye->setPosition(0,osg::Vec3(10.0f,5.0f,5.0f));treeBillboard_rot_world->setPosition(0,osg::Vec3(5.0f,5.0f,5.0f));treeBillboard_rot_axial->setPosition(0,osg::Vec3(15.0f,0.0f,0.0f));osg::ref_ptr<osg::PositionAttitudeTransform> treePos = new osg::PositionAttitudeTransform;treePos->setPosition(osg::Vec3(0.0f,0.0f,0.0f));treePos->addChild(tree.get());root->addChild(treeBillboard_rot_axial.get());root->addChild(treeBillboard_rot_world.get());root->addChild(treeBillboard_rot_eye.get());root->addChild(treePos.get());osgViewer::Viewer myViewer;myViewer.setSceneData(root.get());myViewer.realize();myViewer.run();return 0;}