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[SOLVED] - Save and Draw FrameBufferObject from paintEvent



  • Hello everybody,

    I am new using QGLWidget and frameBufferObjects. I have been reading about framebuffer objects because I need overpaint a GL (never to erase the previous GL) and paint some text and lines with QPainter.
    The only solution that I found was use framebuffer to save the GL and then paint the framebuffer with a QPainter, but it's not working.
    I really need a little help please.

    I add the pseudocode:

    @NewClass::NewClass(QWidget *parent): QGLWidget(QGLFormat(QGL::SampleBuffers), parent){
    m_frameBuffer = new QGLFramebufferObject(500, 500, QGLFramebufferObject::Depth);
    (QImage m_savedImage is defined in the class definition)
    }

    void NewClass::ogldraw(){
    // I use the frameBufferObject for painting the current GL draw
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    m_frameBuffer->bind();
    glBegin(GL_POINTS);
    ...
    glEnd();
    m_frameBuffer->release();
    }

    void NewClass::paintEvent(){
    // I use m_savedImage for overpainting the next GL draw to all previous overpainted draw
    QPainter painterToSavedImage(&m_savedImage);
    painterToSavedImage.setCompositionMode(QPainter::CompositionMode_SourceOver);
    painterToSavedImage.drawImage(0, 0, m_frameBuffer->toImage(), Qt::TransparentMode);

    // I try to show the overpainted frameBufferObject
    QPainter painterW(this);
    painterW.setCompositionMode(QPainter::CompositionMode_SourceOver);
    painterW.drawImage(0, 0, m_savedImage,Qt::TransparentMode);
    

    }@

    I don't know why the ogldraw() always draw to screen even if I don't use updateGL neither repaint.
    Why the m_frameBuffer drawn into m_savedImage is not working?

    Please I want to learn why I don't get the expected result.

    Thanks,

    Fred



  • I got it.
    The makeCurrent context must be set in the constructor or in the initializeGL.

    Fred


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