[boost] Re: [gui] rectangles and the CSS box model

From: Reece Dunn (msclrhd_at_[hidden])
Date: 2004-12-22 05:57:58

Alan Gutierrez wrote:
> * Reece Dunn <msclrhd_at_[hidden]> [2004-12-22 05:22]:
> 
>>Hi All,
>>
>>In the "thoughts on a GUI component library" thread there have been 
>>various discussions about the layout of a rectangle and come relating to 
>>CSS. Note that point and size are stable.
>>
>>The CSS3 Values and Units module 
>>(http://www.w3.org/TR/2001/WD-css3-values-20010713/) defines various 
>>units (e.g. inches, picas and em). This is a good basis for a GUI 
>>library metric type. The type should store the values as a floating 
>>point to allow things like 2.71cm and also to support platforms that 
>>store coordinates as floating points (e.g. Cocoa).
>>
>>The CSS3 relative values (em and ex) are dependant on the inherited 
>>font-size property, so it is difficult to use these units as there is no 
>>associated font-size property. Another issue relating to this is how to 
>>resolve metric values between units that are not directly convertable. I 
>>have suggested using a device::resolve method that takes metric, point, 
>>size and rect types, but it may not always be possible to get access to 
>>a device.
> 
> 
>     Maybe, in this sense, a font is a "device" that can resolve?

Maybe what would be better is a css_device, since this would allow 
font-size property inheriting and resolution of the em unit. It should 
therefore be possible to extend/override the default resolution 
behaviour for a device:

struct device
{
    virtual metric resolve_unit( metric v, metric::type t, orientation o );
    inline point resolve( const point & p, metric::type t )
    {
       return point
       (
          resolve_unit( p.x, t, orientation::x_axis ),
          resolve_unit( p.y, t, orientation::y_axis )
       );
    }
    // similar resolve method for size and rect
};

Therefore the css_device would override the resolve_unit method.

Regards,
Reece