How to vizualize Images from different threads in real time?

Question

I have 4 camera objects. Each camera Object refreshes frames independently. I would like to visualize these frames on my videowall class. Basicly, my videowall is just a gridlayout child with draw Widget methods.

Each camera object has imageHolder widget. ImageHolder widget is a child of qOpenglWidget with

void OpenGLImageHolder::display(const QImage* img)
{
    m_image = img;
    this->update();
}

void OpenGLImageHolder::paintEvent(QPaintEvent*)
{

    QPainter painter(this);
    painter.drawImage(this->rect(), *m_image);
}

Each Image Holder has a QTimer and QTimer::timeOut() is connected to OpenGLImageHolder::display().

Unfortunatelly, with this setup, I can visualize only 3 cameras simultaniously. If I add 4th camera, one of three (or two) freezes. I know that display was called, because when I resizeWidget, I get a correct Image update.

What is the right way to make videoWall? Shall I make one openglWidget with its own window, and then draw images directly on this openglWidget? Which tools can I use to profile the behaviour (it seems that standart msvs profiler is not enough).

Answer 1

My design:

Each camera uses a thread that prepares an image. The image is created when needed or by a timer. When it's ready, the thread signals the main thread.

The main thread handles the signal. Loads the image to the GPU as a texture an draw it by a simple quad.

The trick is to use an unique window, but a different glViewport for each camera.

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Other solution is to use a texture for the whole window and update the rectangle each camera uses.