Using a QQuickPaintedItem for the rendering. The item gets the library
name from the model and loads the decoration with its own decoration
plugin. Thus each preview has its own plugin which eliminates the need to
constantly recreate the decoration as it is done with the preview.
Having a QQuickItem gives new possibilities. The item accepts hover
events and forwards them as enter and leave events to the widgets inside
the decoration. By that the mouse interaction of e.g. Oxygen is still
functional. If the decoration uses the new update approach the bridge is
forwarding the updates to the item and triggering a repaint so we even
have animations in the preview although the widget is never shown.
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