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  1. Qt
  2. QTBUG-98048

Drag and drop with pixmap laggy on KDE



    • Bug
    • Resolution: Done
    • P3: Somewhat important
    • 6.5.0 Beta1
    • 6.2.1
    • GUI: Drag and Drop
    • Arch Linux KDE Plasma 5.23.2, Qt 6.2.1, Compositor enabled, Morphing Popups Effect enabled
    • Linux/X11
    • 180b496b53 (qt/qtbase/dev) 180b496b53 (qt/tqtc-qtbase/dev)


      Drag and drop is very sluggish and laggy when attaching a Pixmap to the drag and when having the compositor enabled on KDE. This is because KDE animates the position of all tooltip windows, which means that KDE interpolates the position of the image, which causes very high latency.

      This is because Qt sets the Qt::ToolTip flag for QShapedPixmapWindow here: https://code.woboq.org/qt5/qtbase/src/gui/kernel/qshapedpixmapdndwindow.cpp.html#59

       setFlags(Qt::ToolTip | Qt::FramelessWindowHint | Qt::X11BypassWindowManagerHint | Qt::WindowTransparentForInput | Qt::WindowDoesNotAcceptFocus);

      In my opinion, it should not set the Qt::ToolTip flag, as this is not a tooltip, but a pixmap that follows the cursor across the whole desktop. Would it be a problem if that specific flag was removed?


      Related Qt forum post from 2016: https://forum.qt.io/topic/73975/qml-drag-drop-starts-late-lags-behind-and-is-sluggish


      The relevant source code of the KDE compositor animation can be found here: https://github.com/KDE/kwin/blob/master/src/effects/morphingpopups/package/contents/code/morphingpopups.js#L20


      The imageSource example right from the Qt docs is a minimal reproducable example to cause the high latency of the drag and drop image: https://doc-snapshots.qt.io/qt6-dev/qml-qtquick-drag.html#imageSource-attached-prop


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              vimpostor Magnus Groß
              vimpostor Magnus Groß
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