Re: [Gnome-print] Pango and gnome-print

[Lauris Kaplinski <lauris ximian com>]

Hello!

First, I am not sure, whether we are talking about the same thing,
or not ;-)
To have glyphlist-like entry point in gnome-print is must be
for WYSIWYG work - where you have to deal with screen-printer
(different resolutions) consistency.
Aso of convenience entry points - that by definition are not
WYSIWYG - yes, we can add pangolayout based method instead of text
based one.
It involves 2 things:
a) Gnome-print has to supply Pango with font metrics for given
   printer. I do not know, how this is handled, but certainly
   it is possible, if pango can use correct metrics for certain
   screen resolution.
b) Pango layout will be converted to glyphlists internally.
Now this theoretically can produce crap in several cases - basically
if final printer resolution is not known during printing. But as
we are talking about convenience methods here, this is not
too big problem. Serious apps have to use glyphlists anyways.

I'll outline the problem with pangolayout one more time.
In pangolayout each glyph has fixed coordinates. So it is
terribly sensitive about real output resolution - if the one
used for metrics and actual one mismatch, you will possibly get
ugly visible artefacts in text (imagine word 'lill' in small
font, where all 3 inter-glyph distances are not equal).
But very probably there are plenty of situations, where the actual
output resolution is not known during job creation. So some
reasonable default (600dpi) should be used. Glyphlists
try to push final glyph placement into further stage of
pipeline, where there is more chance, that resolution is settled.
With Pangolayout, you risk with artefact from the first stage.

Best wishes,
Lauris Kaplinski

On 15 Jun 2001 15:59:00 +0100, Tony Graham wrote:
> Lauris Kaplinski wrote at  2 Jun 2001 00:18:22 +0200:
>  > On 01 Jun 2001 18:03:39 +0100, Tony Graham wrote:
> ...
>  > > >From what I have read in the mail archives, I can't work out why Pango
>  > > is being described as one day being used inside gnome-print as if
>  > > Pango isn't being used by other programs.
> ...
>  > > I'm probably splitting hairs, and it may be exactly what Lauris means, 
>  > > but if your application is concerned with how much goes on the page,
>  > > you just want to worry about the size of the text block, not how to
>  > > translate that into terms that the print system understands.  Since
>  > > Pango already has multiple rendering contexts, it would be useful if
>  > > gnome-print didn't add another one.
>  > 
>  > Agreed. But we need rendering context, suitable for multi-resolution.
> 
> Pango has two: one based on FreeType 2, and one based on XFT (which is 
> based on FreeType).
> 
> ...
>  > But - until XRender is not ubiquitious, it will be major pain
>  > to establish any screen-printer consistency here :(
> 
> I didn't say that I wanted screen-printer consistency.
> 
> If, before I print, I use Pango to work out the extents of a block of
> text that I want to place on a page, and if gnome-print eventually
> uses Pango to work where to place the glyphs representing that text,
> why can't I cut out the second use of Pango (and/or save having to
> build glyphlists) and just pass the Pango layout to gnome-print?
> 
> Regards,
> 
> 
> Tony Graham
> ------------------------------------------------------------------------
> Tony Graham                           mailto:tony.graham@ireland.sun.com
> Sun Microsystems Ireland Ltd                       Phone: +353 1 8199708
> Hamilton House, East Point Business Park, Dublin 3            x(70)19708
> 
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