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Qt 15.5.0 DPI scaling touch screen problem (EGLFS)



  • Dear all,

    I have connected a new display to my Raspberry Pi 4B because I had driver problems with my previous one. The new one has a resolution of 800x480 pixels, a capacitive touch screen and a DSI connection. After setting QT_QPA_EGLFS_KMS_ATOMIC=1 my application starts. Display and touch screen seem to work correctly.

    However, due to the high resolution of the display, the displayed characters are very small. As the physical size of the screen is not detected by Qt (veryfied with Qt logging), I have set QT_QPA_EGLFS_PHYSICAL_WIDTH and QT_QPA_EGLFS_PHYSICAL_HEIGHT to the correct values (95 by 54 mm) in /etc/environment. When I now start my application, characters and buttons are bigger but my application does no longer react to touch events, though the touches are recognized by the application (verified with qDebug() << ((QMouseEvent *) event)->screenPos()). The positions that are reported are as expected (between 0,0 and 799,479) and not rotated.

    Has anybody an idea what is going on here?

    Thank you very much for your help!

    Kind regards,

    Ralf


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