On 2/15/12 9:26 AM, "ext Thiago Macieira" <thiago.macie...@intel.com> wrote:
>On quarta-feira, 15 de fevereiro de 2012 07.38.44, >gunnar.sle...@nokia.com >wrote: >> Our initial idea was to change "qreal" to "double" to avoid any >>potential >> regression but the impact on size combined with the fact that the added >> precision is almost never needed changed our minds >> (https://bugreports.qt-project.org/browse/QTBUG-23758) > >There is one reason for choosing double though: it can store any 32-bit >integer without loss of precision. So doubles can be used to pass around >pixel >coordinates that are 32-bit integers. That's the reason Wayland chose to >use >it for all coordinates. > >Float has 24 bits of mantissa precision, which is enough for >16777216x16777216 >pixels. Probably good enough I'd say. > >I think the most important thing is to unify the definition. Every time I >met >someone from Canonical, they asked me about it because trying to build Qt- >based software on ARM revealed lots of float-double mistakes. > >Note: changing qreal to float is source-incompatible and requires manual >fixups >where it breaks. But it's not silent. I don't think it'll break too many places though, so I'm not too worried about the change. Choosing float has my vote, as it'll use a lot less memory and is the right thing in the common case. It also directly maps to OpenGL types. Let's rather use double explicitly where needed. Cheers, Lars _______________________________________________ Development mailing list Development@qt-project.org http://lists.qt-project.org/mailman/listinfo/development
