[osg-users] Resizing FBO camera while rendering

Rômulo Cerqueira romulogcerqueira at gmail.com
Mon Oct 1 20:34:58 PDT 2018


I have rendered a FBO camera to image by using a callback (as seen in the code below), however some OpenGL warnings/erros are raised when I resize at runtime by setupViewer() method. I debugged the code by using 


and got the following error:

Warning: detected OpenGL error 'invalid operation' after applying attribute Viewport 0x7fb35406e500

How can I properly do the resizing of my FBO camera?

// create a RTT (render to texture) camera
osg::Camera *ImageViewerCaptureTool::createRTTCamera(osg::Camera* cam, osg::Camera::BufferComponent buffer, osg::Texture2D *tex, osg::GraphicsContext *gfxc)
    osg::ref_ptr<osg::Camera> camera = cam;
    camera->setClearColor(osg::Vec4(0, 0, 0, 1));
    camera->setClearMask(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    camera->setRenderOrder(osg::Camera::PRE_RENDER, 0);
    camera->setViewport(0, 0, tex->getTextureWidth(), tex->getTextureHeight());
    camera->attach(buffer, tex);
    return camera.release();

// create float textures to be rendered in FBO
osg::Texture2D* ImageViewerCaptureTool::createFloatTexture(uint width, uint height)
    osg::ref_ptr<osg::Texture2D> tex2D = new osg::Texture2D;
    tex2D->setTextureSize( width, height );
    tex2D->setInternalFormat( GL_RGB32F_ARB );
    tex2D->setSourceFormat( GL_RGBA );
    tex2D->setSourceType( GL_FLOAT );
    tex2D->setResizeNonPowerOfTwoHint( false );
    tex2D->setFilter( osg::Texture2D::MIN_FILTER, osg::Texture2D::LINEAR );
    tex2D->setFilter( osg::Texture2D::MAG_FILTER, osg::Texture2D::LINEAR );
    return tex2D.release();

void ImageViewerCaptureTool::setupViewer(uint width, uint height, double fovY)
    // set graphics contexts
    osg::ref_ptr<osg::GraphicsContext::Traits> traits = new osg::GraphicsContext::Traits;
    traits->x = 0;
    traits->y = 0;
    traits->width = width;
    traits->height = height;
    traits->pbuffer = true;
    osg::ref_ptr<osg::GraphicsContext> gfxc = osg::GraphicsContext::createGraphicsContext(traits.get());

    // set the main camera
    _viewer = new osgViewer::Viewer;
    osg::ref_ptr<osg::Texture2D> tex = createFloatTexture(width, height);
    osg::ref_ptr<osg::Camera> cam = createRTTCamera(_viewer->getCamera(), osg::Camera::COLOR_BUFFER0, tex, gfxc);
    cam->setProjectionMatrixAsPerspective(osg::RadiansToDegrees(fovY), (width * 1.0 / height), 0.1, 1000);

    // render texture to image
    _capture = new WindowCaptureScreen(gfxc, tex);

osg::ref_ptr<osg::Image> ImageViewerCaptureTool::grabImage(osg::ref_ptr<osg::Node> node)
    // set the current node

    // if the view matrix is invalid (NaN), use the identity
    if (_viewer->getCamera()->getViewMatrix().isNaN())

    // grab the current frame
    return _capture->captureImage();

////WindowCaptureScreen METHODS

WindowCaptureScreen::WindowCaptureScreen(osg::ref_ptr<osg::GraphicsContext> gfxc, osg::Texture2D* tex) {
    _mutex = new OpenThreads::Mutex();
    _condition = new OpenThreads::Condition();
    _image = new osg::Image();

    // checks the GraficContext from the camera viewer
    if (gfxc->getTraits()) {
        _tex = tex;
        int width = gfxc->getTraits()->width;
        int height = gfxc->getTraits()->height;
        _image->allocateImage(width, height, 1, GL_RGBA, GL_FLOAT);

WindowCaptureScreen::~WindowCaptureScreen() {
    delete (_condition);
    delete (_mutex);

osg::ref_ptr<osg::Image> WindowCaptureScreen::captureImage() {
    //wait to finish the capture image in call back
    return _image;

void WindowCaptureScreen::operator ()(osg::RenderInfo& renderInfo) const {
    osg::ref_ptr<osg::GraphicsContext> gfxc = renderInfo.getState()->getGraphicsContext();

    if (gfxc->getTraits()) {

        // read the color buffer as 32-bit floating point
        renderInfo.getState()->applyTextureAttribute(0, _tex);
        _image->readImageFromCurrentTexture(renderInfo.getContextID(), true, GL_FLOAT);

        // grants the access to image


Thanks in advance,


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