Learning OSG programing---Multi Camera in one window 在單視窗中建立多相機

　　在學習OSG提供的例子osgCamera中，由于例子很長，涉及很多細節，考慮将其分解為幾個小例子。本文介紹實作在一個視窗中添加多個相機的功能。

　　此函數接受一個Viewer引用類型參數，設定圖形上下文的特征變量traits,并由它建立圖形上下文。根據需要差建立的相機數量，循環建立相機變量，并将其添加到觀察器變量中，作為從相機。每次建立相機，都需要擷取目前圖形上下文，并設定相機的起點（左下角）坐标和相機的寬度與高度。相機間的差別僅在于相機起點的不同。完整的程式代碼如下。

void singleWindowMultipleCameras(osgViewer::Viewer& viewer)
{
    osg::GraphicsContext::WindowingSystemInterface* wsi = osg::GraphicsContext::getWindowingSystemInterface();
    if (!wsi)
    {   
        osg::notify(osg::NOTICE)<<"Error, no WindowSystemInterface available, cannot create windows."<<std::endl;
        return;
    }

    unsigned int width, height;
    osg::GraphicsContext::ScreenIdentifier main_screen_id;

    main_screen_id.readDISPLAY();
    main_screen_id.setUndefinedScreenDetailsToDefaultScreen();
    wsi->getScreenResolution(main_screen_id, width, height);

    osg::ref_ptr<osg::GraphicsContext::Traits> traits = new osg::GraphicsContext::Traits;
    traits->x = 0;
    traits->y = 0;
    traits->width = width;
    traits->height = height;
    traits->windowDecoration = true;
    traits->doubleBuffer = true;
    traits->sharedContext = 0;
    traits->readDISPLAY();
    traits->setUndefinedScreenDetailsToDefaultScreen();

    osg::ref_ptr<osg::GraphicsContext> gc = osg::GraphicsContext::createGraphicsContext(traits.get());
    if (gc.valid())
    {
        osg::notify(osg::INFO)<<"  GraphicsWindow has been created successfully."<<std::endl;

        // need to ensure that the window is cleared make sure that the complete window is set the correct colour
        // rather than just the parts of the window that are under the camera's viewports
        gc->setClearColor(osg::Vec4f(0.2f,0.2f,0.6f,1.0f));
        gc->setClearMask(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    }
    else
    {
        osg::notify(osg::NOTICE)<<"  GraphicsWindow has not been created successfully."<<std::endl;
    }

    unsigned int numCameras = 3;
    double aspectRatioScale = 1.0;///(double)numCameras;
    for(unsigned int i=0; i<numCameras;++i)
    {
        osg::ref_ptr<osg::Camera> camera = new osg::Camera;
        camera->setGraphicsContext(gc.get());
        camera->setViewport(new osg::Viewport((i*width)/numCameras,(i*height)/numCameras, width/numCameras, height/numCameras));
        GLenum buffer = traits->doubleBuffer ? GL_BACK : GL_FRONT;
        camera->setDrawBuffer(buffer);
        camera->setReadBuffer(buffer);

        viewer.addSlave(camera.get(), osg::Matrixd(), osg::Matrixd::scale(aspectRatioScale,1.0,1.0));
    }
}      

　　之後在主函數中調用建立多相機函數，為觀察器添加從相機，并向觀察器中加入模型，進行顯示。主函數代碼如下：

int main(){
    osgViewer::Viewer viewer;
    singleWindowMultipleCameras(viewer);
    viewer.setSceneData(osgDB::readRefNodeFile("cow.osg"));
    return viewer.run();
}      

　　運作程式，可顯示多相機效果，如下所示：

　　可以更改singleWindowMultipleCameras函數中的numCameras變量，建立更多的從相機。

　　建立多相機的關鍵是相機視點的設定和向觀察器中添加從相機。而程式最開始的建立視窗系統接口，圖形上下文，圖形上下文特征以及相機的緩沖設定，則是一些輔助性工作。

轉載于:https://www.cnblogs.com/SupremeGIS-Developer/p/10685269.html