OSG嵌入QT的简明总结

目录

1.解决方案

不得不说关于osg的资料实在太零散了，搜索了很多关于osg在qt下的解决方案，都是各有各的说法，有的说的不是很清楚，有的已经过时了。这里提供一下自己的解决方案吧。
在远古的osg里面，应该是提供对qt的支持的；不过应该是由于qt版本变动比较大，现在的osg版本应该已经没有了。但是在github上又有了新的osgqt项目（地址：https://github.com/openscenegraph/osgqt） 用来解决这个问题。
osgqt是个简单的小项目，其实没有必要额外的编译，最核心的是个名为graphicswindowqt的类，只需要复制graphicswindowqt.h和graphicswindowqt.cpp到qt工程里面就可以使用了。同时osgqt给出了一个名为osgviewerqt的样例，也仅仅只是个cpp文件。结合两者，一个简单的示例就出来了。
qt工程如下：

编译运行后如下：

2.存在问题

1) 警告提示

上述项目直接运行，会出现诸如“qopenglcontext::swapbuffers() called with non-exposed window, behavior is undefined”的警告。查阅网上的英文资料，大意说是因为opengl环境未初始化产生的。在osgviewerqt中绑定了一个定时器，每隔10ms就调用frame()来绘制一帧，而这个定时器是在构造函数的时候就开始调用了，没有等待qt中opengl环境的生成。在这里我把定时器的部分给改进了一下，等待osg的环境初始化完成在启动定时器，这个警告就没有了。osgviewerqt改进后的代码如下：

#include <qtimer>
#include <qapplication>
#include <qgridlayout>

#include <osgviewer/compositeviewer>
#include <osgviewer/viewereventhandlers>

#include <osgga/multitouchtrackballmanipulator>

#include <osgdb/readfile>

#include "graphicswindowqt"

#include <iostream>

class viewerwidget : public qwidget, public osgviewer::compositeviewer
{
public:
    viewerwidget(qwidget* parent = 0, qt::windowflags f = 0, osgviewer::viewerbase::threadingmodel threadingmodel=osgviewer::compositeviewer::singlethreaded) : qwidget(parent, f)
    {
        setthreadingmodel(threadingmodel);

        // disable the default setting of viewer.done() by pressing escape.
        setkeyeventsetsdone(0);

        qwidget* widget1 = addviewwidget( creategraphicswindow(0,0,100,100), osgdb::readrefnodefile("d:/work/osgbuild/openscenegraph-data/cow.osgt") );
        qwidget* widget2 = addviewwidget( creategraphicswindow(0,0,100,100), osgdb::readrefnodefile("d:/work/osgbuild/openscenegraph-data/glider.osgt") );
        qwidget* widget3 = addviewwidget( creategraphicswindow(0,0,100,100), osgdb::readrefnodefile("d:/work/osgbuild/openscenegraph-data/axes.osgt") );
        qwidget* widget4 = addviewwidget( creategraphicswindow(0,0,100,100), osgdb::readrefnodefile("d:/work/osgbuild/openscenegraph-data/fountain.osgt") );
//        qwidget* popupwidget = addviewwidget( creategraphicswindow(900,100,320,240,"popup window",true), osgdb::readrefnodefile("d:/work/osgbuild/openscenegraph-data/dumptruck.osgt") );
//        popupwidget->show();

        qgridlayout* grid = new qgridlayout;
        grid->addwidget( widget1, 0, 0 );
        grid->addwidget( widget2, 0, 1 );
        grid->addwidget( widget3, 1, 0 );
        grid->addwidget( widget4, 1, 1 );
        setlayout( grid );

        //connect( &_timer, signal(timeout()), this, slot(update()) );
        //_timer.start( 10 );
    }

    qwidget* addviewwidget( osgqt::graphicswindowqt* gw, osg::ref_ptr<osg::node> scene )
    {
        osgviewer::view* view = new osgviewer::view;
        addview( view );

        osg::camera* camera = view->getcamera();
        camera->setgraphicscontext( gw );

        const osg::graphicscontext::traits* traits = gw->gettraits();

        camera->setclearcolor( osg::vec4(0.2, 0.2, 0.6, 1.0) );
        camera->setviewport( new osg::viewport(0, 0, traits->width, traits->height) );

        // set the draw and read buffers up for a double buffered window with rendering going to back buffer
        camera->setdrawbuffer(gl_back);
        camera->setreadbuffer(gl_back);

        camera->setprojectionmatrixasperspective(30.0f, static_cast<double>(traits->width)/static_cast<double>(traits->height), 1.0f, 10000.0f );

        view->setscenedata( scene );
        view->addeventhandler( new osgviewer::statshandler );
        view->setcameramanipulator( new osgga::multitouchtrackballmanipulator );
        gw->settoucheventsenabled( true );
        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(); }

    //定时器事件
    void timerevent(qtimerevent* )
    {
        frame();
    }

    //启动定时器绘制
    void show()
    {
        qwidget::show();
        _timerid = starttimer(10);
    }


protected:

    //qtimer _timer;
    int _timerid;               //定时器id
};

int main( int argc, char** argv )
{
    osg::argumentparser arguments(&argc, argv);

#if qt_version >= 0x050000
    // qt5 is currently crashing and reporting "cannot make qopenglcontext current in a different thread" when the viewer is run multi-threaded, this is regression from qt4
    osgviewer::viewerbase::threadingmodel threadingmodel = osgviewer::viewerbase::singlethreaded;
#else
    osgviewer::viewerbase::threadingmodel threadingmodel = osgviewer::viewerbase::culldrawthreadpercontext;
#endif

    while (arguments.read("--singlethreaded")) threadingmodel = osgviewer::viewerbase::singlethreaded;
    while (arguments.read("--culldrawthreadpercontext")) threadingmodel = osgviewer::viewerbase::culldrawthreadpercontext;
    while (arguments.read("--drawthreadpercontext")) threadingmodel = osgviewer::viewerbase::drawthreadpercontext;
    while (arguments.read("--cullthreadpercameradrawthreadpercontext")) threadingmodel = osgviewer::viewerbase::cullthreadpercameradrawthreadpercontext;

#if qt_version >= 0x040800
    // required for multithreaded qglwidget on linux/x11, see http://blog.qt.io/blog/2011/06/03/threaded-opengl-in-4-8/
    if (threadingmodel != osgviewer::viewerbase::singlethreaded)
        qapplication::setattribute(qt::aa_x11initthreads);
#endif

    qapplication app(argc, argv);
    viewerwidget* viewwidget = new viewerwidget(0, qt::widget, threadingmodel);
    viewwidget->setgeometry( 100, 100, 800, 600 );
    viewwidget->show();
    return app.exec();
}

2) 多线程问题

在osg中提供了诸如culldrawthreadpercontext等多线程模式，但是在这里是没办法支持这些多线程模式的，只能支持单线程。在网上查阅了一些解决方案，但是最后都不是很完美，有空再把其解决方案写出来。

3) 其他

graphicswindowqt最终继承的还是qt中的qglwidget类，提供opengl功能。而在新版本的qt中，这个类已经被废弃了，取而代之的是一个叫做qopenglwidget的类。所以这里面问题还是不少的，好在内容相对较少，以后有空可以自己改进。