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  1. Qt
  2. QTBUG-133057

Guard shaders from eating too much RAM sliently

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    • Linux/Yocto

    Description

      This is something I cannot reproduce, but it is said that on 1GB version of Raspberry Pi 4 (I only have 4GB version so I couldn't reproduce the issue whatsoever), if there are too many shadows and blurs with paddingRect then the entire application is going to freeze and crash due to:

      Out of memory: Killed process 1709.
      

      Indeed, we warn users about performance considerations:
      https://doc.qt.io/qt-6/qml-qtquick-effects-multieffect.html#paddingRect-prop
      and like:
      https://doc.qt.io/qt-6/qml-qtquick-effects-multieffect.html#blur-prop
      But maybe we can improve it by making it even clearer? Or have some sort of warning output in the code? Because a crash, especially on certain target due to RAM capacity, feels quite serious a problem.

      Update: the original reporter mentioned that the problem does not happen back in Qt6.5. But their app starts to crash since 6.8. Still, I cannot reproduce. But if anyone has a 1GB RPi4, he/she can try that. And this may imply a regression in performance and this report may worth a P1.

      Update: reproducer attached. There is a TextInput whose text is copied into a Text which is further used as the source of MultiEffect. That is where problem happens - the Multieffect applies shadows and blurs with paddingRect. Reportedly, on a 1BG RPi4 when you input enough letters then the app is going to freeze and possibly get killed. Like what the video shows.

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            kagro Kaj Grönholm
            luqiaochen Luqiao Chen
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