osg19讲（Control）

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最新推荐文章于 2023-05-01 14:24:46 发布

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文章标签： c++

本文链接：https://blog.youkuaiyun.com/qq970767225/article/details/128003752

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本文深入解析了OSG Viewer的构造及关键源码，包括View类的初始化过程与ViewerBase类中渲染循环的具体实现细节。

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osg结构图
在这里插入图片描述
其中每个类分别解析：

osg::view

关键源码：

View::View():
    Object(true)
{
    // OSG_NOTICE<<"Constructing osg::View"<<std::endl;

    setLightingMode(HEADLIGHT);//设置灯光模式 （头灯，环境灯）

    _camera = new osg::Camera;//创建一个默认相机
    _camera->setView(this);

    double height = osg::DisplaySettings::instance()->getScreenHeight();
    double width = osg::DisplaySettings::instance()->getScreenWidth();
    double distance = osg::DisplaySettings::instance()->getScreenDistance();
    double vfov = osg::RadiansToDegrees(atan2(height/2.0f,distance)*2.0);

    _camera->setProjectionMatrixAsPerspective( vfov, width/height, 1.0f,10000.0f);

    _camera->setClearColor(osg::Vec4f(0.2f, 0.2f, 0.4f, 1.0f));//设置背景颜色

    osg::StateSet* stateset = _camera->getOrCreateStateSet();
    stateset->setGlobalDefaults();
}

osg::viewerbase

关键源码：
run->frame

void ViewerBase::frame(double simulationTime)
{
    if (_done) return;

    // OSG_NOTICE<<std::endl<<"CompositeViewer::frame()"<<std::endl<<std::endl;

    if (_firstFrame)
    {
        viewerInit();

        if (!isRealized())
        {
            realize();
        }

        _firstFrame = false;
    }
    advance(simulationTime);

    eventTraversal();
    updateTraversal();
    renderingTraversals();
}

int ViewerBase::run()
{
    if (!isRealized())
    {
        realize();
    }

    unsigned int runTillFrameNumber = osg::UNINITIALIZED_FRAME_NUMBER;
    osg::getEnvVar("OSG_RUN_FRAME_COUNT", runTillFrameNumber);

    while(!done() && (runTillFrameNumber==osg::UNINITIALIZED_FRAME_NUMBER || getViewerFrameStamp()->getFrameNumber()<runTillFrameNumber))//是否关闭
    {
        double minFrameTime = _runMaxFrameRate>0.0 ? 1.0/_runMaxFrameRate : 0.0;
        osg::Timer_t startFrameTick = osg::Timer::instance()->tick();
        if (_runFrameScheme==ON_DEMAND)
        {
            if (checkNeedToDoFrame())
            {
                frame();
            }
            else
            {
                // we don't need to render a frame but we don't want to spin the run loop so make sure the minimum
                // loop time is 1/100th of second, if not otherwise set, so enabling the frame microSleep below to
                // avoid consume excessive CPU resources.
                if (minFrameTime==0.0) minFrameTime=0.01;
            }
        }
        else
        {
            frame();
        }

        // work out if we need to force a sleep to hold back the frame rate
        osg::Timer_t endFrameTick = osg::Timer::instance()->tick();
        double frameTime = osg::Timer::instance()->delta_s(startFrameTick, endFrameTick);
        if (frameTime < minFrameTime) OpenThreads::Thread::microSleep(static_cast<unsigned int>(1000000.0*(minFrameTime-frameTime)));//控制帧数
    }

    return 0;
}

void ViewerBase::viewerBaseInit()
{
    _firstFrame = true;//是否是第一帧，若为第一帧会调用viewerInit（）
    _done = false;//是否继续渲染
    _keyEventSetsDone = osgGA::GUIEventAdapter::KEY_Escape;//设置退出键
    _quitEventSetsDone = true;
    _releaseContextAtEndOfFrameHint = true;//结束后是否释放上下文

    _threadingModel = AutomaticSelection;//渲染线程
    _threadsRunning = false;//线程状态
    _endBarrierPosition = AfterSwapBuffers;//线程同步
    _endBarrierOperation = osg::BarrierOperation::NO_OPERATION;
    _requestRedraw = true;//重新绘制
    _requestContinousUpdate = false;

    _runFrameScheme = CONTINUOUS;//帧更新策略
    _runMaxFrameRate = 0.0f;//帧数（通过计算当前帧数，若大于设置帧数则sleep休眠）

    std::string str;
    if (osg::getEnvVar("OSG_RUN_FRAME_SCHEME", str))
    {
        if      (str=="ON_DEMAND") _runFrameScheme = ON_DEMAND;
        else if (str=="CONTINUOUS") _runFrameScheme = CONTINUOUS;
    }

    osg::getEnvVar("OSG_RUN_MAX_FRAME_RATE", _runMaxFrameRate);

    _useConfigureAffinity = true;
}