Re: gEDA-user: gschem with cairo rendering

[Peter Clifton <pcjc2@xxxxxxxxx>]

On Sun, 2008-05-04 at 16:34 +0100, Peter Clifton wrote:
> On Sun, 2008-05-04 at 15:22 +0000, Kai-Martin Knaak wrote:
> > On Sat, 03 May 2008 15:10:14 +0100, Peter Clifton wrote:
> > 
> > > Yes, that's exactly the right diagnosis. Cairo supports glyphs and
> > > fonts, just not ones defined at run-time by the user of its API. (IE.
> > > gschem can't yet describe to cairo what it thinks the various glyphs
> > > should look like),
> > 
> > I couldn't care less for the font currently used by gschem. It is just 
> > plain ugly when zoomed in. If it were replaced by a real font, the only 
> > important property is a compatible font metrics. 
> 
> I think gschem's font is a little larger than its metrics claim. Ales
> can correct me if I'm wrong, but I believe the code defines a 2pt font
> as 26 mils high. (That matches roughly the "real" conversion factor of
> 27.7778). I've tried either, but the "Sans" font on my system
> consistently comes out smaller than the gschem font.

Judging by the code, which scales line lengths of the primitive font by
"size / 2" (size being in points), this would suggest that gschem's
primitive font is a 2pt font, and whichever metric corresponds to the
notional point size of a font, should measure 26 mils in those glyph
definitions.

> Looking at its metrics (dig into gschem/src/o_text.c and change the
> #undef DEBUG_TEXT #define DEBUG_TEXT), I see that its ascent and height
> are quite large compared to the size of the glyphs I'm actually seeing.
> 
> BTW.. Please take a play and see what fonts you like. Search for "Sans"
> in o_text.c.
> 
> > > Unfortunately, the glyph caching won't help with zoom either, since the
> > > first time you render a glyph at a given size, it will be slow.
> > 
> > A glyph like "a" is reused many times on a view with lots of text. So it 
> > has to be rendered only once and can be copied for the rest of the 
> > instances. I'd expect glyph caching to help in this situation. If the 
> > current view contains only little text, speed is no issue in the first 
> > place.  
> 
> Yes, it helps lots over the case where I was rendering text using lines
> (old code, converted to cairo lines). The main thing is that you have up
> to 26 x 2 + (extras) glyphs to render for each size you zoom to. That
> can take time a noticable time, and is one of the things limiting the
> zoom frame-rate.
> 
> Best wishes,
> 
-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)



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