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From Jeremias Maerki <...@jeremias-maerki.ch>
Subject Re: AFP Font Question
Date Wed, 04 Mar 2009 13:33:29 GMT
To a certain degree, it is already possible using the Intermediate
Format. You'd generate the IF file using the font metrics for the PDF
output but render the IF file to AFP output. The tricky thing is to
synchronize the font setups for PDF and AFP (especially the font names)
so there won't be any font selection problems when generating the AFP.
However, the devil is in the detail: for performance reasons we don't
store the position of each individual glyph. This is what would be
necessary to achieve a maximum of "equalness". Otherwise, little
differences in the native font metrics can accumulate to a visible
difference in the final output if you have long strings or use things
like letter-/word-spacing. So much for what is possible today...

It is thinkable that a special subclass of AFPPainter would be written
that has a special drawText() method which could use an additional
FontInfo object set up for a PDF renderer to calculate individual glyph
positions but then paint the glyphs using normal AFP infrastructure.
Just so there are no illusions: that comes with a performance penalty. I
can also not guarantee that the result is much better than the above.
Depends on the documents.

Technically correct is what works and doesn't have a negative impact on
the overall system. ;-) At any rate, it's possible.

So I guess that lists the downsides also. Let's also look at other
possible solutions:

Normal AFP outline fonts are nothing other than Type1 PFB fonts embedded
in a FOCA resource. Type1 fonts are cheap. One could experiment by
writing a program that can turn a Type1 font into a FOCA outline font by
generating the necessary data structures (general and glyph metrics)
from the original font files. However, there's a certain risk that font
generated like this may not have optimal values everywhere so some
differences could result from this. However, I consider the risk here
relatively small as we're speaking about a scalable font. But you also
have to take into account the cost involved writing such a converter.

Another approach would be to generate bitmap fonts from Type 1 or
TrueType fonts. Creating bitmap images of single glyphs is easy. However,
bitmap fonts are usually manually optimized for the various sizes and
target resolutions which an automated program probably couldn't do that
well. The same risk as for the converted Type 1 font applies, only the
risk of suboptimal output is definitely higher.

Going further: modern AFP/IPDS environments allow to directly use
TrueType fonts as data object resources. FOP could be taught to use
TrueType fonts which would make it possible to use the same font for PDF
and AFP. Of course, if it's no option to uprade an old AFP/IPDS
environment...

Finally, there are various tools on the market (ex. Compart's DocBridge
Mill) which can convert AFP to PDF. That would entirely bypass the
problem. However, PDFs generated that way may not offer the same
feature-set that FOP can offer and the generated files might be bigger
than FOP-generated PDFs.

HTH

On 04.03.2009 09:47:11 Chris Bowditch wrote:
> Hi All,
> 
> one of my clients is using the PDF and AFP Renderers to produce the same 
> document via different outputs. PDF is for archiving and AFP for 
> Printing. However, currently the output between the 2 is different. The 
> AFP output line breaks differently to the PDF version, with the text 
> appearing larger and bolder despite the font size being the same between 
> the output channels. After some investigation I realised that the cause 
> of the problem was the use of raster AFP Fonts. When I tested PDF and 
> AFP output using TTF in PDF and an equivalent outline Font in AFP the 
> output looks identical. So I thought great and told the client to switch 
> to Outline Fonts in AFP.
> 
> However, my client doesn't want to do that. Apparently there would be 
> some large costs to purchase all the outline fonts necessary for their 
> large collection of existing documents. My client has asked if it is 
> possible to enhance FOP to use metrics from TTF or Type1 Fonts when 
> working with AFP raster Fonts, and just use the glyphs from the raster 
> font. This would ensure output between PDF and AFP looks identical. I 
> know XEP does something similar. Is this enhancement feasible? Is it 
> technically correct to use metrics from one font type and use the glyphs 
> from other. Is there any downside?
> 
> Comments would be appreciated.
> 
> Thanks,
> 
> Chris



Jeremias Maerki


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