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Forum Update on Monday, May 27th 2025

QT widget based UI rendering slow on qt5 when ported from qt4

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  • SGaistS SGaist

    Widgets are using the rasteriser backend, so if you are thinking GPU, no they are not hardware accelerated.

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    L Offline
    linuxsnail
    wrote on last edited by
    #15

    @SGaist 0_1537246791995_QT_Graphics_Framework.png

    I came across one slide recently about QT presemtation. Does this mean that Qwidget can be accelerated as well?

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    • K Offline
      K Offline
      kuzulis
      Qt Champions 2020
      wrote on last edited by
      #16

      @linuxsnail said in QT widget based UI rendering slow on qt5 when ported from qt4:

      Does this mean that Qwidget can be accelerated as well?

      Seems no.

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      • SGaistS Offline
        SGaistS Offline
        SGaist
        Lifetime Qt Champion
        wrote on last edited by
        #17

        IIRC, DirectFB provided some hardware acceleration depending on the graphic chip you have at your disposal but don't expect NVIDIA Titan X acceleration performances.

        Interested in AI ? www.idiap.ch
        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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        • SGaistS SGaist

          IIRC, DirectFB provided some hardware acceleration depending on the graphic chip you have at your disposal but don't expect NVIDIA Titan X acceleration performances.

          L Offline
          L Offline
          linuxsnail
          wrote on last edited by
          #18

          @SGaist Can I use EGLFS for QWidgets without GPU support? Do you think it can have better performance over LinuxFB?

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          • SGaistS SGaist

            IIRC, DirectFB provided some hardware acceleration depending on the graphic chip you have at your disposal but don't expect NVIDIA Titan X acceleration performances.

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            L Offline
            linuxsnail
            wrote on last edited by
            #19

            @SGaist I am still struggling with this topic, is there any possibility of adding software acceleration for qwidgets ? I'm just wondering what made it render faster on qt 4.8.1? even when we use qt4.8.7 it seems slow like qt5.

            For qt4.8.1 and 4.8.7 my compile configurations are similar.

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            • SGaistS Offline
              SGaistS Offline
              SGaist
              Lifetime Qt Champion
              wrote on last edited by
              #20

              If you are seeing a slowdown between Qt 4.8.1 and Qt 4.8.7, you should compare the code of both backend to see what's going on.

              Interested in AI ? www.idiap.ch
              Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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              • SGaistS SGaist

                If you are seeing a slowdown between Qt 4.8.1 and Qt 4.8.7, you should compare the code of both backend to see what's going on.

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                linuxsnail
                wrote on last edited by
                #21

                @SGaist Sure that's what I am doing right now but on a separate note is it possible to use any software acceleration with QTWidgets?

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                • SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #22

                  What software acceleration do you have in mind ?

                  Interested in AI ? www.idiap.ch
                  Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                  • SGaistS SGaist

                    What software acceleration do you have in mind ?

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                    linuxsnail
                    wrote on last edited by
                    #23

                    @SGaist i just want to understand can opengl or svg libraries be used without gpu or any other backend like directfb can improve performance rendering apart from linuxfb

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                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #24

                      You can use mesa for software based OpenGL rendering (don't expect hight performance).

                      SVG is not a screen rendering backend.

                      IIRC DirectFB should be faster than plain LinuxFB.

                      Interested in AI ? www.idiap.ch
                      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                      • SGaistS SGaist

                        You can use mesa for software based OpenGL rendering (don't expect hight performance).

                        SVG is not a screen rendering backend.

                        IIRC DirectFB should be faster than plain LinuxFB.

                        L Offline
                        L Offline
                        linuxsnail
                        wrote on last edited by
                        #25

                        @SGaist Ok I believe qt 4 has qt-gfx driver which provides some sort of software acceleration when used with linux fb, any idea qt5 has any such driver which I can use?

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                        • SGaistS Offline
                          SGaistS Offline
                          SGaist
                          Lifetime Qt Champion
                          wrote on last edited by
                          #26

                          You have the complete list of backend available here.

                          Interested in AI ? www.idiap.ch
                          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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