On 2/15/12 12:53 PM, "ext andre.poen...@nokia.com" <andre.poen...@nokia.com> wrote:
> >> Sletta Gunnar (Nokia-MP/Oslo) wrote: >> - Using "double" is pure waste for a lot of use cases. QRectF, >>QPointF, QPainter, QPolygonF, >> OpenGL, QMouseEvent, QTouchEvent, to name a few. None of these require >>the precision >> offered by double precision floating point. > >Whether having doubles in a QPolygonF or a QRectF is necessary depends on >what you are doing with it. If you restrict it to the the current >Qt-internal use cases, 'float' is possibly fine, if you use it for >general coordinate handling in, say, GIS it is certainly not. > >> The only questionable use case is geolocation. We know for a fact that >>floats have limitations >> in this area and both Qt3D and QtLocation make use of QVector[2|3|4]D >>and QMatrix4x4 which >> will now be a float. However, this is no worse (for device) than it >>already is, > >It won't be worse in the _embedded_ case (and even there only for the >embedded cases that did not use a custom build of Qt with hard-coded >'double' for qreal). Right... > >I seem to remember we had this kind of discussion in ~2006 already, and >back then the resolution was to have "double" at least on the desktop >side to cover the GIS cases. Sending someone to the wrong side of a 100m >wide river just because the navigation system insisted on using single >precision float seemed inacceptable at that time. Just a small nitpick: You won't end up on the wrong side of the river. The earth has a diameter of around 40000km. With 24 bits precision, you end up with a jitter of just above 2m. You might get wet feet though ;-) Cheers, Lars > > >Anyway. It's probably better to go for any kind of uniformity. If that's >single precision, it should be made clear that QPolygonF/QRectF are not >meant for applications needing "polygons" in general. Maybe one should >consider adding some QPolygonD/QRectD/... later to get the functionality >back. Until these exist, it might be worthwhile to keep the (then >unconditional) typedef though, to allow easy creation of custom builds of >Qt with double precision coordinates. > >Andre' >_______________________________________________ >Development mailing list >Development@qt-project.org >http://lists.qt-project.org/mailman/listinfo/development _______________________________________________ Development mailing list Development@qt-project.org http://lists.qt-project.org/mailman/listinfo/development
