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LinuxFB: top-left offset depends on mmsize - bug or feature?

  • This issue appeared after upgrading Qt from 5.7.1 to 5.12.2. My application running in Debian on BeagleBone Black with LinuxFB backend got shifted by 11x11px from the top-left corner. I discovered that the shift can be controlled by the "mmsize" option, which I never needed to use before.

    The picture below shows how the application is shifted with different values passed with "mmsize". Really big numbers eliminate the offset, e.g. 4000x3000. The LCD's resolution is 800x600 and its physical size is 210x159mm.

    Why it behaves that way? If it's a feature, how it's supposed to be used? Also, the "offset" option doesn't work for me at all.

    By the way, the same setup with VNC backend perfectly works without any additional options.

    Thanks for ideas/directions!


  • Lifetime Qt Champion


    Looks like it could be a regression. Did you check the release logs to see if there's anything related to that ?

  • @SGaist , I couldn't find anything related to that "feature" in the released logs.
    More over, I looked through the source code of 5.12.2 and couldn't find how the variable mPhysicalSize (calculated out of the command-line option) is actually used...

  • Lifetime Qt Champion

    Then you should check the bug report system to see if it's something known. If not, please consider opening a new report providing all the findings you made.

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