Performance Discrepancy Between QOpenGLWidget and freeGLUT in High-FPS Rendering

leom0311

Hello,

I am working on a rendering application where I use both QOpenGLWidget (with Qt) and freeGLUT (in C++) to render images. However, I have noticed a significant performance difference between the two in terms of frames per second (FPS), and I am looking for advice on how to optimize the performance of QOpenGLWidget to match that of freeGLUT.

In my application, I render two 1920x1080 images using freeGLUT, and I am able to achieve around 5000 FPS. However, when rendering a single 1920x1080 image using QOpenGLWidget, the FPS drops significantly to around 1500 FPS. While I understand that Qt might introduce some overhead compared to freeGLUT, I am wondering if there are specific optimization techniques or settings within QOpenGLWidget that could help bring its performance closer to that of freeGLUT.

Here are a few details about my setup:

Both environments are using OpenGL for rendering.
I have disabled VSync in both contexts to maximize FPS.
I am primarily using QOpenGLWidget for its integration with the rest of my Qt-based UI.

Is there any way to optimize QOpenGLWidget in a manner that can help me achieve FPS rates closer to those seen with freeGLUT? Any advice on improving rendering performance in QOpenGLWidget or minimizing Qt-related overhead would be greatly appreciated.

Thanks

// This is my QSurfaceFormat setting
QSurfaceFormat fmt;
fmt.setVersion(2, 0);  // Set to the highest OpenGL version your system supports
fmt.setRenderableType(QSurfaceFormat::OpenGL);
fmt.setSwapBehavior(QSurfaceFormat::DoubleBuffer);
fmt.setSwapInterval(QSurfaceFormat::DefaultSwapBehavior);  // Disable VSync to get the highest FPS
fmt.setProfile(QSurfaceFormat::CoreProfile);  // Use the Core profile for modern OpenGL

// ...
// QMyOpenGLWidget is inherited from QOpenGLWidget
void QMyOpenGLWidget::init() {
    m_qTimer = new QTimer(this);
    m_qTimer->setTimerType(Qt::PreciseTimer);
    connect(m_qTimer, SIGNAL(timeout()), this, SLOT(timeout()));
    m_qTimer->start(0);
}

// ...
void QMyOpenGLWidget::timeout()  {
    update();
}

// ...
void QWidgetPlay::paintGL() {
    if (m_bIsRendering) {
        return;
    }
    m_bIsRendering = true;

    QPainter p;
    p.begin(this);
    p.setRenderHints(QPainter::SmoothPixmapTransform);
    p.drawImage(QPoint(0, 0), m_imgTest1920_1080);
    p.end();
    m_bIsRendering = false;
}

DerReisende

Having no experience with OpenGL I would assume part of the „performance loss“ you see is caused by using the Qt signal slot mechanism. You could measure the delay between timeout calls but I guess this is one of the sources.
But I am asking myself two questions:

Do you really need to render with 1500 or 5000 fps? Noone going to see the differences.
Why don‘t you use a separate render thread and update the UI at a lower rate with the result images?

leom0311

Thanks for your answer.
I don't want to rendering with high-fps like 1500~5000.
I just want to know performance between QOpenGLWidget and freeGLUT.
I mean why QOpenGLWidget is slower than freeGLUT.
Thanks again.

leom0311

I used X2L for game machine.
When I render a1920x1080 image with freeGLUT, I can get fps up to over 100.
But in case of QOpenGLWidget, I can't get even 20 fps.
So I decided to use X4, but I want to know the reason.
Thanks

https://radxa.com/products/x/x2l