October 19, 2011

tiftof tiftof
Lab Rat
7 posts

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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