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QGraphicsEffect: difference between drawing source in logical and device coordinates

  • When looking at the source of QGraphicsOpacityEffect, I see this line:

    Qt::CoordinateSystem system = sourceIsPixmap() ? Qt::LogicalCoordinates : Qt::DeviceCoordinates;

    I understand why you would want to use device coordinates when the source is a pixmap (avoid ugly pixmap scaling), but why choose explicitly for logical coordinates when the source is not a pixmap (QImage?)? Why not always draw in device coordinates?

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