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Does a qt5 virtual framebuffer exist?

  • Ok, so i'm totally new to Qt and am trying to get up to speed for a new embedded project that I'm going to be working on. I have both Qt4 and Qt5 installed on my host machine (running Fedora). I can successfully create a Qt5 Widget Application that runs from Qt Creator. I can also compile and run my app using qmake-qt5 and make.

    But now I would like to see what the app would look like on a monochrome display so I thought i could run it with -platform linuxfb while running the Qt Virtual Framebuffer from Qt4. However, when i do this, the virtual frame buffer runs just fine (with a blank screen obviously) but my app shows the following errors:

    Unable to figure out framebuffer device. Specify it manually.
    linuxfb: Failed to initialize screen
    no screens available, assuming 24-bit color
    Cannot create window: no screens available
    Abort (core dumped)

    The error implies that I need to tell it which display to actually use but I am not sure how to do that. I have tried various things, such as using -display QVFb:0 as described here:

    But that didn't seem to work.

    I feel like I am missing something fundamental here. Can i run a Qt 5 application against a Virtual Framebuffer or is that not supported?

    Thanks in advance for any help you can give me.

  • Lifetime Qt Champion

    Hi and welcome to devnet,

    AFAIK, QVfb is a Qt 4 only feature

  • @SGaist Ok thanks for the response!

  • Lifetime Qt Champion

    Out of curiosity, why monochrome ?

  • @SGaist not my choice :-) Our hardware / business team has price targets they need to meet. I guess they feel that color is too expensive!

  • Lifetime Qt Champion

    I see...

    Depending on your device you should directly work with it like e.g. the Raspberry Pi

  • @SGaist yes i plan to do that eventually... i'm just waiting on co-worker to provide me the proper toolchain / deployment mechanism for our custom board. I was hoping to jumpstart my development using the virtual framebuffer capabilities. Maybe i should just do my app in QT4? Is there any benefit to QT5 that I'd be missing... as you can imagine the GUI will be a very simple monochrome display with no touch screen or mouse. The end product is a desk phone so the input is just buttons.

    Thanks for your time! I appreciate it.

  • Lifetime Qt Champion

    To jumpstart you can indeed go with Qt 4 and the virtual frame buffer. Be aware however that Qt 4 will only see one more patch release (AFAIK) but no more minor release. Once you have your board, you can always go on Qt 5

  • @SGaist Do you have any idea why they dropped support for the virtual framebuffer in Qt5?

  • Lifetime Qt Champion

    No, I don't know that. You can try asking in the #qt IRC channel on freenode or the interest mailing list

  • sir,i am using qt5 version with beaglebone black and 7'' inch lcd screen to display through hdmi cable and i am project using following command
    sudo QT_QPA_PLATFORM=linuxfb ./BBB-Qt

    but i get following errror,

    Unable to figure out framebuffer device. Specify it manually.
    linuxfb: Failed to initialize screen
    Segmentation fault

    can you please help me

  • @neha9 I had the same problem:

    Failed to mmap framebuffer (Invalid argument)
    linuxfb: Failed to initialize screen
    Segmentation fault

    Have you solved it yet?

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