Re: Absolute font sizes

[Owen Taylor <otaylor redhat com>]

On Tue, 2006-10-31 at 15:46 -0500, Behdad Esfahbod wrote:
> On Tue, 2006-10-31 at 12:02 +0100, Kristian Rietveld wrote:
> > Hey Behdad,
> 
> Hey Kris,
> 
> > We noticed this week that nothing in GTK+ currently checks whether the 
> > font size returned by pango_font_description_get_size() is absolute or not.
> 
> This is a very unfortunate side effect of the fact that absolute size
> was added in a much later version than normal sizes.  And indeed a
> horrible API design choice to add
> pango_font_description_get_size_is_absolute() instead of
> pango_font_description_get_absolute_size().

And .. how would you implement the latter? :-)

> Now the confusing parts are:
> 
>   - For PS/PDF, a device unit is one point.  This is ok as long as you
> don't mess up with the fontmap resolution which takes a default of 72
> for PS/PDF backends, but if you confuse them and set something like
> 300dpi or 600dpi, god knows what happens :)
> 
>   - All the stuff above completely ignores any scale you may have on
> your PangoContext.  That's not very common though.
> 
> 
> > I hope you can enlighten us, so the backends can be brought in sync and 
> > GTK+ be fixed :)
> 
> I think the Pango uses are fine.  GTK+ never uses
> pango_font_description_set_absolute_size(). That's good.  But I see one
> can set a font_desc property on a texttag, and that may have absolute
> size.  Also, in other places, GTK+ creates a font description from an
> string.  Until very recently that always generated non-absolute font
> descriptions, but (in 1.14 I guess) I added ability to parse sizes like
> 18px to result in font descriptions with absolute sizes.  So, you want
> to check that.

BTW, if you want to size things to match a font description, the best
way to do that is:
 
 pango_context_get_metrics()

I can't think of many cases in which you want to take a font description
and try to figure out what the specified font size is in pixels.
 
					- Owen