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Displaying images outside the GUI thread (Boost thread)



  • Hi all,
    I am developing a C++ library realizing its interface by means of Qt, using VS2015. On the library side, 3 boost threads continously load images from 3 folders. I am trying to display these images in 3 different QLabel (or equivalent QWidgets), so the thread body consists of this functionality, in particular by exploiting the setPixmap method. Although the call to the function is protected by a boost mutex, I got exceptions probably due to threads synchronization. Looking for a solution, I already awared that the QPixmap widget is not "thread-safe" (non-reentrant). I also tried to use QGraphicsView but it in turn relies on QPixmap, thus I came across the same problem. So my question is: does an alternative to QPixmap exist to display images in Qt in a thread-safe manner?



  • Hi, welcome to the forum.
    All painting has to be done in the GUI thread.



  • Thanks for the anwer! By the way I solved using signal/slot: the "non-GUI" thread emits a signal instead of displaying the images and the called slot paints the QLabel inside the GUI thread!


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    Note that you can use QImage which is hardware independent for painting on from threads (see the mandelbrot example) however as @Wieland wrote the GUI itself can only be update from the main thread.


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