[cairo] Re: Cairo font size should be in units

[Robert O'Callahan]

Owen Taylor wrote:

>On Wed, 2004-09-29 at 15:46 -0400, Carl Worth wrote:
>>/ On Wed, 29 Sep 2004 15:16:43 -0400, Owen Taylor wrote:
>/>/ > On Tue, 2004-09-28 at 18:49 -0700, Bill Spitzak wrote:
>/>/ > > On Tuesday 28 September 2004 06:25 pm, graydon hoare wrote:
>/>/ > >
>/>/ > > > well, no, actually that's not true; cairo builds its CTM in terms of
>/>/ > > > physics. when you start up a cairo program, you have no reason to believe
>/>/ > > > that 1 user unit == 1 pixel. if you want that to be true, the first thing
>/>/ > > > you need to do is ask about DPI and reverse the physics-based
>/>/ > > > transformation. cairo's supposed to support writing
>/>/ > > > (semi)resolution-independent clients, after all.
>/>/ > 
>/>/ > I consider this a misfeature of Cairo:
>/>/ 
>/>/ I should point out that Graydon's description of the default CTM in
>/>/ cairo is missing one important aspect. For display-devices[*], the
>/>/ default CTM is computed by computing 1 unit == 1/96 inch, and then
>/>/ rounding that to the nearest pixel size.
>/
>I think I've characterized this in previous mail as a nasty suprise
>awaiting developers as soon as the first user's screen goes above
>the threshold for 2-pixels-per-unit.
>
For the record, what Carl said is exactly what we want for Mozilla. 
There's an extended discussion of units issues, some of which are 
Mozilla-specific, here:
http://www.ocallahan.org/mozilla/units.html

Rob

-- 
Robert O'Callahan <robert at ocallahan.org>
"In the beginning was the Word, and the Word was with God, and the Word
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