What is the difference between QRect and QRectF?

[d_stranz]

why the QRect and the QRectF were built? please explain,thank you.

With Qt 4, the coordinate system used in painting was changed from integer-based (pixels) to floating point (world coordinates). This permitted scaling and other transformations to be specified and performed more precisely, without rounding errors. In order to not break all existing code, a new set of floating point coordinate classes (QRectF, QSizeF, QPointF, etc.) was introduced side-by-side with the integer versions, and painting operations were extended to use the new floating point classes without changing the pre-existing integer methods.