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

From: Joel de Guzman (joel_at_[hidden])
Date: 2005-10-05 08:27:31

Vladimir Prus wrote:

> I'm trying to say that the choice of coordinate unit -- pixel, millimeter,
> inch, whatever, is only important if you need to write:
> 
>    window.setWidth(10cm);
> 
> and in a proper GUI library you should never set width to absolute value
> like that. Instead, you should do:
> 
>    window.setWidth(screen_width()*some_constant);
> 
> In that case "screen_width()" can return SomeVeryOpaqueType that you can
> multiply by float, but can't convert to pixel, or to to inch, or to
> anything else.

Hmmmm....

I'm not sure about this. Say for example that I am writing a WYSIWYG
CAD application and I'd like to draw vertical and horizontal rulers.
At 100% page view, I'd like the ruler to be a 1:1 with the actual
screen at the designated resolution (say 72 DPI). How would I draw
my ruler if the coordinates are abstracted in terms of percentage?

(Aside: I'd want my app to remain consistent when in the future we
get 200 DPI screens, BTW).

IMO, we should choose one representation and one unit. In my mind,
that would be float and millimeter (in addition to percentages).

Cheers,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net