Re: [boost] GUI coordinate units (Was: GUI foundations)

From: Dave Harris (brangdon_at_[hidden])
Date: 2005-10-05 12:59:18

In-Reply-To: <di0kc7$6th$1_at_[hidden]>
joel_at_[hidden] (Joel de Guzman) wrote (abridged):
> IMO, we should choose one representation and one unit. In my mind,
> that would be float and millimeter (in addition to percentages).

Why float rather than double? Generally picking float is an optimisation, 
and often a premature one. Sooner or later I think you will need the extra 
precision of double, and then you'll have an unnecessary conversion - 
possibly two, if the native device uses ints. Double => float => int.

Why millimeter rather than inch or point? For text, there is a strong 
argument for using imperial rather than metric units. A point is 1/72th of 
an inch, so it converts nicely. Points don't convert so well to 
millimeters. Also, PDF and Postscript are points-oriented. I wouldn't buck 
the trend without a good reason.

-- Dave Harris, Nottingham, UK.