用OpenSceneGraph实现的NeHe OpenGL教程 - 第一课
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简介
NeHe教程是目前针对初学者来说最好的OpenGL教程，它可以带领读者由浅入深，循序渐进地掌握OpenGL编程技巧。到目前为止，NeHe教程一共有48节。我的计划是使用OpenSceneGraph来实现所有48节课程同样的效果。目的是在回归OpenGL知识的同时，学习OpenSceneGraph。对于OpenScenGraph(以后简称osg)我自己掌握的并不是太好，希望借助教程的整体学习，对osg有一个更全面的了解，由于本人能力有限，特别是处于学习阶段，因此在代码中不可避免的存在一些不足，我随时期待读者的指正和交流。转载请注明。谢谢。
在本系列教程中，我使用的是VisualStudio 2008作为开发环境，使用Qt4.8.3版本，OpenScenGraph使用的是3.2.0，建立的工程都是Qt Console类的工程
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创建一个osg窗口
osg3.0后的版本在建立窗口时相对比较简单，因为osg引入了osgQt类库帮助我们建立Qt界面
对于需要将 OSG 嵌合到各式各样的GUI 系统（如MFC，Qt，wxWidgets 等）来
说，osg::GraphicsContext 类是经常要打交道的对象之一。一种常用的嵌入方式实现过程如下所示：
例如X、Y 位置，宽度和高度，以及父窗口的句柄（inheritedWindowData）；然后根据特性
的设置创建一个新的图形设备上下文（GraphicsContext），将其赋予场景所用的摄像机。
对于需要将 OSG 嵌合到各式各样的GUI 系统（如MFC，Qt，wxWidgets 等）来
说，osg::GraphicsContext 类是经常要打交道的对象之一。一种常用的嵌入方式实现过程如下所示：
osg::ref_ptr<osg::GraphicsContext::Traits> traits = new osg::GraphicsContext::Traits; osg::ref_ptr<osg::Referenced> windata = new osgViewer::GraphicsWindowWin32::WindowData(hWnd); traits->x = 0; traits->y = 0; …… traits->inheritedWindowData = windata; osg::GraphicsContext* gc = osg::GraphicsContext::createGraphicsContext(traits.get()); Camera* camera = viewer.getCamera(); camera->setGraphicsContext(gc); …… viewer.setCamera(camera);这个过程虽然比较繁杂，但是顺序还是十分清楚的：首先设置嵌入窗口的特性（Traits），
例如X、Y 位置，宽度和高度，以及父窗口的句柄（inheritedWindowData）；然后根据特性
的设置创建一个新的图形设备上下文（GraphicsContext），将其赋予场景所用的摄像机。
由于使用的是Qt，因此首先使用Traits创建一个GraphicsWindowQt
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());将创建好的GraphicsWindow设置给相机，同时设置相机的视口、投影参数 、 背景颜色
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 );
最后声明窗体类，在这里我定义了渲染的窗体ViewerWidget继承于QWidget和osgViewer::Viewer，同时设置一个定时器，在定时器timeout的时候调用viewer的帧重绘函数。
最后在main函数中设置窗体的大小为640x480，编译并运行，一个如NeHe教程中黑色背景的窗口就出现了。
附：本课源码(源码可能存在错误和不足之处，仅供参考)
1.osgNeHe.h
#ifdef _DEBUG #pragma comment(lib, "OpenThreadsd.lib") #pragma comment(lib, "osgd.lib") #pragma comment(lib, "osgAnimationd.lib") #pragma comment(lib, "osgDBd.lib") #pragma comment(lib, "osgFXd.lib") #pragma comment(lib, "osgGAd.lib") #pragma comment(lib, "osgManipulatord.lib") #pragma comment(lib, "osgParticled.lib") #pragma comment(lib, "osgQtd.lib") #pragma comment(lib, "osgShadowd.lib") #pragma comment(lib, "osgSimd.lib") #pragma comment(lib, "osgTerraind.lib") #pragma comment(lib, "osgTextd.lib") #pragma comment(lib, "osgUtild.lib") #pragma comment(lib, "osgViewerd.lib") #pragma comment(lib, "osgVolumed.lib") #pragma comment(lib, "osgWidgetd.lib") #else #pragma comment(lib, "OpenThreads.lib") #pragma comment(lib, "osg.lib") #pragma comment(lib, "osgAnimation.lib") #pragma comment(lib, "osgDB.lib") #pragma comment(lib, "osgFX.lib") #pragma comment(lib, "osgGA.lib") #pragma comment(lib, "osgManipulator.lib") #pragma comment(lib, "osgParticle.lib") #pragma comment(lib, "osgQt.lib") #pragma comment(lib, "osgShadow.lib") #pragma comment(lib, "osgSim.lib") #pragma comment(lib, "osgTerrain.lib") #pragma comment(lib, "osgText.lib") #pragma comment(lib, "osgUtil.lib") #pragma comment(lib, "osgViewer.lib") #pragma comment(lib, "osgVolume.lib") #pragma comment(lib, "osgWidget.lib") #endif
2.main.cpp
#include "../osgNeHe.h"
#include <QtCore/QTimer>
#include <QtGui/QApplication>
#include <QtGui/QVBoxLayout>
#include <osgViewer/Viewer>
#include <osgDB/ReadFile>
#include <osgQt/GraphicsWindowQt>
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 );
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;
};
int main( int argc, char** argv )
{
QApplication app(argc, argv);
ViewerWidget* viewWidget = new ViewerWidget();
viewWidget->setGeometry( 100, 100, 640, 480 );
viewWidget->show();
return app.exec();
}