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From Jeremias Maerki <dev.jerem...@greenmail.ch>
Subject Re: PDF Transcoder: Revisiting transcoder setup
Date Mon, 16 Aug 2004 20:02:27 GMT
(comments inline)

On 15.08.2004 22:53:16 Thomas DeWeese wrote:
> Jeremias Maerki wrote:
> > Thomas (and all),
> > 
> > I'm currently tracking down differences between the PDF and PS
> > transcoders. The following thread triggered that:
> > http://nagoya.apache.org/eyebrowse/BrowseList?listName=fop-user@xml.apache.org&by=thread&from=825221
> > 
> > There's an SVG attached to the first post. It's a SVG with width and
> > height specified but without a viewBox. In the EPS transcoder the file
> > showed correctly, at first. At least until I changed the resolution from
> > 96dpi to 300dpi. The PDF transcoder did the whole thing wrong because
> > it's now working at a fixed 72dpi as per your patch:
> > http://marc.theaimsgroup.com/?l=fop-dev&m=106795227230411&w=2
> > 
> > I didn't question that patch back then, but I'm now curious why you
> > think it is necessary to use a fixed resolution. You say it's the
> > default user space of PDFGraphics2D. I'd say there is no resolution in
> > PDF, only the resolution at which some SVG constructs will be rendered
> > as bitmaps when they cannot (yet) be expressed natively. 
>     This is almost right.  The problem is that the PDF transcoder
> starts with one userspace unit equal to one 'pt' (1/72nd of an inch).
> Without my patch the generated PDF files for documents that specified
> a size using a real world unit were off by 96/72.  I suspect that your
> EPS files will have similar issues.

Right. Default userspace unit in PostScript is 1pt. PDF and PostScript
are similar in many aspects.

> > In the EPS transcoder I've managed to make it work at every resolution 
> > in the meantime (fixes not committed, yet) by generating the right initial
> > transforms. I believe this can be applied to PDF, too.
>     Yes, I suspect that we could fix this by adding a scale by
> 72/getPixelUnitToMillimeter() before rendering the document (My
> original thought was to have the PDFGraphics do much of this work,
> which might have some advantages but would be a lot more work).

I'm not sure what you mean here, but if it made the behaviour of
PDFGraphics too much SVG/Batik-specific I wouldn't be too happy. I'd
like to use it for different purposes, too: Java Printing System, custom
printables, a FOP renderer that uses Java2D to render to PDF.... I'm
pretty sure the problems can be handled using the right setup code.

> > The limitation to 72dpi in the PDF transcoder has the undesired side
> > effect of outputting embedded images in a very low quality. Removing it
> > improved quality a lot here.
>      Yah, my original thought was to have the PDFGraphics2D rasterize
> at something like 150-300dpi (configurable of course) but provide an
> initial transform of 1 unit = 72 dpi.

see above.

> > But I still have one problem with the above SVG file without viewBox. In
> > the PDF transcoder the images is too big. If I manually put a viewBox="0
> > 0 533 266" into the SVG file then it comes out correctly in PDF.
> > Obviously, the SVG file is made for a 96dpi environment which explains
> > the behaviour. A solution to this problem would be if I could ask Batik
> > to give me the effective (outermost) viewBox even if none is available.
> > Does something like that exist? I didn't find anything.
>     This would be a violation of the SVG specification.  You should not
> 'create' a transform where the user has not requested one.  The one 
> place you might use something like this is if the user does not
> provide a width and height - in this case the user agent is free to
> select one.

<fx>bulb over my head blinking on</fx>

>     To answer your question in this case you can ask the root GVT node
> for it's bounds (getBounds()).  In the case of a dynamic document you
> can use getBBox() on the DOM nodes (but that generally doesn't apply 
> here). This is the true geometric bounds of the document but often
> this isn't really what people want - which is why it isn't a good
> idea to just use it anyways.
>     I agree that the document is in error.  It is assuming that all
> user agent's will use 96 pixels to the inch for real work conversion.
> This is a bad assumption, in SVG you must include a viewBox if you
> want to ensure your content will show properly in the useragent's
> window.

Ok, but that means we could (!) provide an optional convenience mechanism
for the user to have his faulty SVG display correctly if he can't
(technically) fix his SVG. I'll try that.

> > Sorry for the long post. I'm not sure I understood the whole thing
> > completely and I'm hoping you (or someone else) might have some
> > additional ideas. Thanks!
>     Looking at this raised two new issues for me.
>     1) It looks like a JDK 1.4 dependency has slipped in:
> java.lang.IllegalArgumentException: Illegal pattern character 'Z'
>          at 
> java.text.SimpleDateFormat.subFormat(SimpleDateFormat.java:472)
>          at java.text.SimpleDateFormat.format(SimpleDateFormat.java:432)
>          at java.text.DateFormat.format(DateFormat.java:300)
>          at 
> org.apache.fop.pdf.PDFObject.formatDateTime(PDFObject.java:231)
>          at org.apache.fop.pdf.PDFInfo.toPDF(PDFInfo.java:159)
>          at org.apache.fop.pdf.PDFObject.output(PDFObject.java:150)
>          at org.apache.fop.pdf.PDFDocument.output(PDFDocument.java:794)
>          at 
> org.apache.fop.svg.PDFGraphics2D.drawImage(PDFGraphics2D.java:505)
>        Can this be fixed?  Batik still targets JDK 1.3.x.

Yes. I will see to that. FOP officially still targets JDK 1.3.x, too,
although some would like that requirement dropped. In that case I will
see to it that the Batik-relevant parts remain 1.3-compatible for the
time being.

Worst of all, the issue in PDFObject may even be my fault.

>     2) I was going to commit a patch that adds support for anti-aliased
>        clipping (for shape-rendering="geometricPrecision").  However
>        this may result in a lot more content being rasterized.  This
>        isn't a big deal within Batik but for transcoding this loses a
>        lot of semantic value.  So I will likely add a method to the
>        UserAgent to check if the user agent want's it to use
>        anti-aliased clipping or not.
>        Does this sound like an acceptable solution?

Sounds good to me.

Jeremias Maerki

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