本课要实现的效果是让三角形绕自身的轴线Y轴进行旋转， 四边形绕自身X轴进行旋转。
在osg中实现这种效果有很多种方法可以做到，无论哪种方法总体的思路是定时地去修改场景中的空间变换节点，本文采用最简单的一种方式进行修改：使用场景中节点的回调来修改空间变换节点从而达到旋转的效果。
首先我们先定义一个场景节点的Callback类，OSG中的节点主要使用回调(Callback)来完成用户临时定义的、需要每帧执行的工作。这是一种方便的扩展节点功能的方式，根据回调功能被调用的时机，OSG节点回调包括更新回调(UpdateCallback)和人机交互事件回调(EventCallback)两种，前者在每一帧系统遍历到当前节点时自动调用，后者则通过用户操作键盘、鼠标、改变窗口等动作发生，触发事件回调。此处我们需要的是一个节点的更新回调，定义如下：
[cpp] view plain copy class RotateCallback : public osg::NodeCallback { public: RotateCallback(osg::Vec3d rotateAxis, double rotateSpeed) : osg::NodeCallback(), _rotateAxis(rotateAxis), _rotateSpeed(rotateSpeed), _rotateAngle(0.0) { //Nop } virtual void operator()(osg::Node* node, osg::NodeVisitor* nv) { osg::MatrixTransform *currentMT = dynamic_cast<osg::MatrixTransform*>(node); if (currentMT) { //获取当前的平移位置 osg::Vec3d currentTranslate = currentMT->getMatrix().getTrans(); osg::Matrix newMatrix = osg::Matrix::rotate(_rotateAngle, _rotateAxis) * osg::Matrix::translate(currentTranslate); currentMT->setMatrix(newMatrix); _rotateAngle += _rotateSpeed; } traverse(node, nv); } private: osg::Vec3d _rotateAxis; //旋转轴 double _rotateSpeed; //旋转速度 double _rotateAngle; //当前旋转的角度 }; 节点回调类都继承于osg::NodeCallback，我们需要做的是重载它里面的operator()方法来实现自定义的代码，定义好之后将回调加入到三角形和四边形的空间变化节点之中：
[cpp] view plain copy osg::MatrixTransform *triangleMT = new osg::MatrixTransform; triangleMT->setMatrix(osg::Matrix::translate(-1.5, 0.0, -6.0)); RotateCallback *triangleRotateCallback = new RotateCallback(osg::Y_AXIS, 0.2); triangleMT->addUpdateCallback(triangleRotateCallback); 以及
[cpp] view plain copy osg::MatrixTransform *quadMT = new osg::MatrixTransform; quadMT->setMatrix(osg::Matrix::translate(1.5, 0.0, -6.0)); RotateCallback *quadRotateCallback = new RotateCallback(osg::X_AXIS, 0.15); quadMT->addUpdateCallback(quadRotateCallback); 编译并运行程序即看到动态的效果
附：本课源码(源码中可能存在错误和不足，仅供参考)
[cpp] view plain copy #include "../osgNeHe.h" #include <QtCore/QTimer> #include <QtGui/QApplication> #include <QtGui/QVBoxLayout> #include <osgViewer/Viewer> #include <osgDB/ReadFile> #include <osgQt/GraphicsWindowQt> #include <osg/MatrixTransform> #include <osg/NodeVisitor> class ViewerWidget : public QWidget, public osgViewer::Viewer { public: ViewerWidget(osg::Node *scene = NULL) { QWidget* renderWidget = getRenderWidget( createGraphicsWindow(0,0,100,100), scene); QVBoxLayout* layout = new QVBoxLayout; layout->addWidget(renderWidget); layout->setContentsMargins(0, 0, 0, 1); setLayout( layout ); connect( &_timer, SIGNAL(timeout()), this, SLOT(update()) ); _timer.start( 10 ); } QWidget* getRenderWidget( osgQt::GraphicsWindowQt* gw, osg::Node* scene ) { osg::Camera* camera = this->getCamera(); camera->setGraphicsContext( gw ); const osg::GraphicsContext::Traits* traits = gw->getTraits(); camera->setClearColor( osg::Vec4(0.0, 0.0, 0.0, 1.0) ); camera->setViewport( new osg::Viewport(0, 0, traits->width, traits->height) ); camera->setProjectionMatrixAsPerspective(45.0f, static_cast<double>(traits->width)/static_cast<double>(traits->height), 0.1f, 100.0f ); camera->setViewMatrixAsLookAt(osg::Vec3d(0, 0, 1), osg::Vec3d(0, 0, 0), osg::Vec3d(0, 1, 0)); this->setSceneData( scene ); return gw->getGLWidget(); } osgQt::GraphicsWindowQt* createGraphicsWindow( int x, int y, int w, int h, const std::string& name="", bool windowDecoration=false ) { osg::DisplaySettings* ds = osg::DisplaySettings::instance().get(); osg::ref_ptr<osg::GraphicsContext::Traits> traits = new osg::GraphicsContext::Traits; traits->windowName = name; traits->windowDecoration = windowDecoration; traits->x = x; traits->y = y; traits->width = w; traits->height = h; traits->doubleBuffer = true; traits->alpha = ds->getMinimumNumAlphaBits(); traits->stencil = ds->getMinimumNumStencilBits(); traits->sampleBuffers = ds->getMultiSamples(); traits->samples = ds->getNumMultiSamples(); return new osgQt::GraphicsWindowQt(traits.get()); } virtual void paintEvent( QPaintEvent* event ) { frame(); } protected: QTimer _timer; }; // //RotateCallback class RotateCallback : public osg::NodeCallback { public: RotateCallback(osg::Vec3d rotateAxis, double rotateSpeed) : osg::NodeCallback(), _rotateAxis(rotateAxis), _rotateSpeed(rotateSpeed), _rotateAngle(0.0) { //Nop } virtual void operator()(osg::Node* node, osg::NodeVisitor* nv) { osg::MatrixTransform *currentMT = dynamic_cast<osg::MatrixTransform*>(node); if (currentMT) { //获取当前的平移位置 osg::Vec3d currentTranslate = currentMT->getMatrix().getTrans(); osg::Matrix newMatrix = osg::Matrix::rotate(_rotateAngle, _rotateAxis) * osg::Matrix::translate(currentTranslate); currentMT->setMatrix(newMatrix); _rotateAngle += _rotateSpeed; } traverse(node, nv); } private: osg::Vec3d _rotateAxis; //旋转轴 double _rotateSpeed; //旋转速度 double _rotateAngle; //当前旋转的角度 }; osg::Node* buildScene() { osg::Group *root = new osg::Group; osg::MatrixTransform *triangleMT = new osg::MatrixTransform; triangleMT->setMatrix(osg::Matrix::translate(-1.5, 0.0, -6.0)); RotateCallback *triangleRotateCallback = new RotateCallback(osg::Y_AXIS, 0.2); triangleMT->addUpdateCallback(triangleRotateCallback); osg::Geometry *triangleGeometry = new osg::Geometry; osg::Vec3Array *triangleVertexArray = new osg::Vec3Array; triangleVertexArray->push_back(osg::Vec3(0.0f, 1.0f, 0.0f)); triangleVertexArray->push_back(osg::Vec3(-1.0f,-1.0f, 0.0f)); triangleVertexArray->push_back(osg::Vec3(1.0f,-1.0f, 0.0f)); triangleGeometry->setVertexArray(triangleVertexArray); osg::Vec4Array *triangleColorArray = new osg::Vec4Array; triangleColorArray->push_back(osg::Vec4(1.0f, 0.0f, 0.0f, 1.0f)); triangleColorArray->push_back(osg::Vec4(0.0f, 1.0f, 0.0f, 1.0f)); triangleColorArray->push_back(osg::Vec4(0.0f, 0.0f, 1.0f, 1.0f)); triangleGeometry->setColorArray(triangleColorArray); triangleGeometry->setColorBinding(osg::Geometry::BIND_PER_VERTEX); triangleGeometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::TRIANGLES, 0, 3)); osg::Geode *triangleGeode = new osg::Geode; triangleGeode->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF); triangleGeode->addDrawable(triangleGeometry); triangleMT->addChild(triangleGeode); //四边形部分 osg::MatrixTransform *quadMT = new osg::MatrixTransform; quadMT->setMatrix(osg::Matrix::translate(1.5, 0.0, -6.0)); RotateCallback *quadRotateCallback = new RotateCallback(osg::X_AXIS, 0.15); quadMT->addUpdateCallback(quadRotateCallback); osg::Geometry *quadGeometry = new osg::Geometry; osg::Vec3Array *quadVertexArray = new osg::Vec3Array; quadVertexArray->push_back(osg::Vec3(-1.0f, 1.0f, 0.0f)); quadVertexArray->push_back(osg::Vec3(1.0f, 1.0f, 0.0f)); quadVertexArray->push_back(osg::Vec3(1.0f,-1.0f, 0.0f)); quadVertexArray->push_back(osg::Vec3(-1.0f,-1.0f, 0.0f)); quadGeometry->setVertexArray(quadVertexArray); osg::Vec4Array *quadColorArray = new osg::Vec4Array; quadColorArray->push_back(osg::Vec4(0.5f,0.5f,1.0f,1.0f)); quadGeometry->setColorArray(quadColorArray); quadGeometry->setColorBinding(osg::Geometry::BIND_OVERALL); osg::DrawElementsUByte *vertexIndices = new osg::DrawElementsUByte(osg::PrimitiveSet::QUADS, 4); vertexIndices->push_back(0); vertexIndices->push_back(1); vertexIndices->push_back(2); vertexIndices->push_back(3); quadGeometry->addPrimitiveSet(vertexIndices); osg::Geode *quadGeode = new osg::Geode; quadGeode->getOrCreateStateSet()->setMode(GL_LIGHTING, osg::StateAttribute::OFF); quadGeode->addDrawable(quadGeometry); quadMT->addChild(quadGeode); root->addChild(triangleMT); root->addChild(quadMT); return root; } int main( int argc, char** argv ) { QApplication app(argc, argv); ViewerWidget* viewWidget = new ViewerWidget(buildScene()); viewWidget->setGeometry( 100, 100, 640, 480 ); viewWidget->show(); return app.exec(); }
