Area Tree vs. subsequent renderer (was Re: FO property expressions)

[Glen Mazza <gl...@yahoo.com>]

Thanks, Peter, for the explanation on the
property/inheritance computations--I have one more
question, perhaps anyone can answer (The Area
Tree/Renderer explanations on the Design Tab is
somewhat vague on this point):  

For those output formats requiring an area tree (i.e.,
non-TXT, RTF, etc.), the area tree is independent of
the renderer, correct?

I.e., the area tree created for a document will be 
the same for all renderers, and the area tree is
created without taking into account its subsequent
renderer.

Thanks,
Glen

--- "Peter B. West" <pb...@powerup.com.au> wrote:
> Glen,
> 
> Sorry about the late reply, but this has only just
> arrived.  See 
> comments below.
> 



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Re: Area Tree vs. subsequent renderer (was Re: FO property expressions)

[Jeremias Maerki <de...@greenmail.ch>]

Peter's right. We've done some loud thinking a few months back (Dec/Jan,
I think) about the possibility to create several output files from the
same area tree. At the moment anyway, the renderer provides the fonts
and the layout engine adjusts to that. So, that means that the area tree
differs depending on the renderer used. That can be improved but only by
making a central font registry. The renderer would then announce which
font sources it supports. It's all in the archives.

On 02.06.2003 14:27:07 Peter B. West wrote:
> > For those output formats requiring an area tree (i.e.,
> > non-TXT, RTF, etc.), the area tree is independent of
> > the renderer, correct?
> > 
> > I.e., the area tree created for a document will be 
> > the same for all renderers, and the area tree is
> > created without taking into account its subsequent
> > renderer.
> 
> In general, no.  Most of the atoms composing the area tree are character 
> glyphs.  How they are composed on the page depends on their metrics. 
> The font metrics may vary from renderer to renderer.  For this reason, 
> the target renderer (or at the very least the font metrics associated 
> with the renderer) must be known.  Jeremias, Victor and others have been 
> concerned with factoring out a fonts subsystem, so they may be able to 
> promise that for FOP this issue will be resolved.
> 
> I know nothing at all about image rendering, but there may also be 
> renderer dependencies in the composition of images.



Jeremias Maerki


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Re: Area Tree vs. subsequent renderer (was Re: FO property expressions)

["Peter B. West" <pb...@powerup.com.au>]

Glen Mazza wrote:
> Thanks, Peter, for the explanation on the
> property/inheritance computations--I have one more
> question, perhaps anyone can answer (The Area
> Tree/Renderer explanations on the Design Tab is
> somewhat vague on this point):  
> 
> For those output formats requiring an area tree (i.e.,
> non-TXT, RTF, etc.), the area tree is independent of
> the renderer, correct?
> 
> I.e., the area tree created for a document will be 
> the same for all renderers, and the area tree is
> created without taking into account its subsequent
> renderer.

Glen,

In general, no.  Most of the atoms composing the area tree are character 
glyphs.  How they are composed on the page depends on their metrics. 
The font metrics may vary from renderer to renderer.  For this reason, 
the target renderer (or at the very least the font metrics associated 
with the renderer) must be known.  Jeremias, Victor and others have been 
concerned with factoring out a fonts subsystem, so they may be able to 
promise that for FOP this issue will be resolved.

I know nothing at all about image rendering, but there may also be 
renderer dependencies in the composition of images.

Peter
-- 
Peter B. West  http://www.powerup.com.au/~pbwest/resume.html


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