用OpenSceneGraph实现的NeHe OpenGL教程 - 第四课
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简介
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。
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实现
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：
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：
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
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)
#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();
}