Custom QQuickPaintedItem looks bad on Raspberry Pi



  • Hello all,
    I wrote a QtQml-based application for a Raspberry Pi 2B+ earlier this year, with plenty of help from these forums :) It's a data recorder for sampling electric values.

    I'm expanding its capabilities, and have run into a problem. It can now support over 240 separate values. Originally I used a custom QQuickPaintedItem, and put in a Flickable so users could scroll through the values. When I run the new version with 240 values, the text becomes blurry, like it's been resized.

    I have some screenshots that show what I mean: https://imgur.com/a/w1LWQ

    My QQuickPaintedItem draws onto a QImage. It appears that when the QImage's height is greater than 2048 pixels, it gets blurry/resized. I wonder if this is related to the Pi's maximum texture size of 2048?

    Can anyone point me in the right direction for making my images not look like a blurry mess?


  • Moderators

    Hi! Not sure what causes it, but your texture-size guess sounds reasonable. For the solution: Wouldn't it be easier anyway to replace the huge image with a listview?



  • I had considered a listview, and cannot recall now why I decided against using it. I will investigate it again.



  • Just a guess, but I also had some issues displaying QQuickPaintedItem with
    large images and it turned out, that the memory split was at a low value.
    After changing it to e.g. 256 M, the Images got displayed correctly.



  • @sneubert How big were your images? I tried setting the GPU memory to 256M, but it didn't make any difference.



  • I rendered pdf DIN A4 pages with 600 dpi via poppler



  • @sneubert Wow that's pretty big. Do you have any other tips for getting good quality? Like maybe the format used for QImage?



  • Sorry i´m just using the QImage generated by poppler. I have no control about the generator.


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