Re: clarification on GtkAlignment

[John Finlay <finlay moeraki com>]

Mark Ivey wrote:

> Wow, that's unfortunate.  I didn't really want to just pad it...that
> almost goes back to the bad days of absolute positioning.
>
> Anyone have any idea why the alignments aren't more "exact" with their
> scales?  Is this intended?
>
> -Mark Ivey-
>
> On Tue, 2004-09-28 at 09:58, Stefan Kost wrote:
>  
>
> > In the GNOME HIG they really suggest to use a label containg spaces for padding
> > (I don't like that as well).
> > That means you should put each button in a hbox(2) and put the padding label
> > into the first slot of the hbox and your button into the second one.
> > :-(
> >
> > Stefan
> >
> > Mark Ivey wrote:
> >    
> >
> > > I don't understand something about alignments, hopefully someone can
> > > help me out.  My window contains a 4-row vbox filled with alignments. 
> > > Each alignment has the same settings:
> > >         x align: 1.0
> > >         y align: 0.0
> > >         x scale: 0.5
> > >         y scale: 1.0
> > > Each alignment also contains a 1 button.  The buttons have different
> > > labels, like this:
> > >         a
> > >         as
> > >         asd
> > >         asdf
> > >
> > > Now, I would expect all the buttons to take exactly half the window, but
> > > they don't.  The buttons with shorter labels are slightly wider.  FWIW,
> > > this happens with labels also, not just buttons
> > >
> > > So what's the deal?  
> > >
> > > My ultimate goal is to have a layout like this, where all the widgets
> > > are lined up 1/3 of the way out from the left edge:
> > >
> > > Section heading
> > > ----------------
> > >     widget
> > >     widget
> > >     widget
> > >
> > > Another section
> > > ----------------
> > >     widget
> > >     widget
> > >
> > >
> > > ...is there a better way to do it?
> > >
> > >      
My understanding of aligments is that they deal with the free space 
beyond that required by the child widget. That means the scale factors 
take the fraction of free space and add it to the child widget required 
space. Likewise the align factors determine the fraction of free space 
to be allocated to the left or above the widget. For example:
A GtkButton widget (32 pixels wide by 32 pixels high) is placed inside a 
GtkAlignment widget (256 pixels wide by 128 pixels high) which has 
xalign of 0.25, yalign of 0.25, xscale of 0.25 and yscale of 0.25. The 
horizontal free space is 256-32=224 pixels and the vertical free space 
is 128-32=96 pixels. The button will absorb 0.25x224=56 pixels 
horizontally and 0.25x96=24 pixels vertically since the xscale and 
yscale are 0.25 and become 32+56=88 pixels wide by 32+24=56 pixels high. 
This will leave 256-88=168 pixels of horizontal free space and 128-56=72 
pixels of vertical free space. Since the xalign value is 0.25 the 
horizontal free space will be allocated as 0.25x168=42 pixels to the 
left of the button and 0.72x168=126 pixels to the right. Likewise given 
a yalign value of 0.25 the vertical free space is allocated as 
0.25x72=18 pixels above the button and 0.75*72=54 pixels below.

John