[solved] Qt and OpenGL

  • Hi Guys!

    I'm trying to use the power of the OpenGL on a Colibri T20 from Toradex. The card is running Linux (Angstrom) with X11 (Xorg).

    I've developped a small piece of code (which is running fine on Windows) with both QWidget and QGLWidget. It's a simple animation on a picture (fade-in/fade-out) When I'm running the version with the QWidget I can see my processor up to 20% and when I'm running it with the QGLWidget, the processor activity looks like the ECG from a reality TV star, so I concluded that my usage of the QGLWidget is correct. :-)

    The problem is when I'm running the code on the card: the animation I've created is sloooooooooooooooooow (with both QGLWidget and QWidget)

    So my question is: Am I really using the hardware accelaration or not? How can I test it? Should I have receive an error from my project during the compilation if OpenGL wasn't installed on the card? Or, is my code optimized? (my opinion: my code is not optimised at all :-) )

    Here is the code of my test widget:

    @#include "glwidget.h"
    #include "QDebug"

    GLWidget::GLWidget(Helper *helper, QWidget *parent)
    : QGLWidget(QGLFormat(QGL::SampleBuffers), parent), helper(helper)
    elapsed = 1;
    reverse = false;

    void GLWidget::animate()
    //elapsed = (elapsed + qobject_cast<QTimer*>(sender())->interval()) % 1000;
    elapsed = elapsed + 0.01;
    elapsed = elapsed - 0.01;

    if(elapsed <= 0 && reverse == false)
        reverse = true;
    else if(elapsed >= 1 && reverse == true)
        reverse = false;


    void GLWidget::paintEvent(QPaintEvent *event)
    QPainter painter;
    helper->paint(&painter, event, elapsed);



    And here the repaint's call

    @GLWidget *openGL = new GLWidget(&helper, this);


    QTimer *timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), openGL, SLOT(animate()));

    Thanks a looooooot!

  • Lifetime Qt Champion

    Hi and welcome to devnet,

    I'm not sure I'm following you right. Since you want to do OpenGL why are you using paintEvent ?

    Also, you are trying to update at 100fps which might be a bit optimistic for an embedded board.

  • Hi,

    Thanks for welcoming me on the forum and for your answer!

    I followed a tutorial on line to create this widget because I've never worked with OpenGL and paint functions. Should I use paintGL and QGLPainter instead?

    I've try to turn down to 10fps, the result seems the same... For my fade-in/out functions, I'm using the painter's setOpacity function, is it the right way?

    What I want to do is simple, just a smooth fade-in/out on a picture :-)

    Thanks for you answer!

  • Lifetime Qt Champion

    Then you might be overcomplicating things, what about this:

    • QLabel -> for your image
    • QGraphicsOpacityEffect -> self-explaining
    • QPropertyAnimation -> to animate the QGraphicsOpacityEffect

    This way everything is automated for you

  • Thanks, but actually I've started to use OpenGL directly because my first try was QPropertyAnimation and QGraphicsOpacityEffect and the result wasn't good too.

    But, good news! I've found a solution... The problem was the picture it self... I used a too big one and because i'm lazy i downscaled the picture to see it entirely on the screen... So I've changed the picture by a picture of 1920x1080 and... Wow, at 100fps, it's smooth as hell! And it use only 5 to 8 percent of the processor!

    Sorry for this thread... My fault... But I've learned a lot and maybe my code will be usefull for somebody else :-)

    Thanks again!

  • Lifetime Qt Champion

    You're welcome !

    Don't be afraid to ask question :)

    Since you have it working now, please update the thread title prepending [solved] so other forum users may know a solution has been found :)

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