用OpenSceneGraph实现的NeHe OpenGL教程 - 第一课

时间：2022-06-20 20:09:34

  • 简介



OpenSceneGraph是一个开放源码，跨平台的图形开发包，它为诸如飞行器仿真，游戏，虚拟现实，科学计算可视化这样的高性能图形应用程序开发而设计。它基于场景图的概念，它提供一个在OpenGL之上的面向对象的框架，从而能把开发者从实现和优化底层图形的调用中解脱出来，并且它为图形应用程序的快速开发提供很多附加的实用工具。
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

  • 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：
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。
用OpenSceneGraph实现的NeHe OpenGL教程 - 第一课

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();
}
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