I have finished the initial implementation of what I call on-the-fly
images in fop. Essentially this is a callback system that has an
object draw itself into a PDFGraphics2D during pdf rendering, rather
than going through intermediate steps such as svg or Images. 

I'm fairly pleased with it, though it did turn up some other
scalability problems.

Initially, plotting one test map took 1.25 minutes; the new version
takes about 8 seconds. The original implementation, using the standard
fop distribution generated an svg
(slow), then loaded the svg (slow), then rendered the svg to the
pdf. The new implementation registers some callbacks for the included
images, and the callbacks render directly.

Memory usage is much better now, as well. We frequently overran the
default 64MB with the original implementation, since the dom-based svg
generation and reloading both ate up the heap. Now I can generally
plot up to E size PDFs (34" x 44"), though for complex maps I still
run out of heap.

Looking into the implementation of PDFRenderer and PDFGraphics2D, it
looks like the memory bottleneck with the new implementation is
probably the fact that 
PDFGraphics2D stores its results in a StringWriter, and then that
StringWriter is appended to the PDFStream's own
ByteArrayOutputStream. This requires twice as much ram as simply
writing directly to the PDFStream.

True scalability, frankly, will require rendering directly to a file,
and keeping as little in RAM as possible. I didn't chase the code to
see how difficult that would be, but I figure it's not trivial. The
benefits would be enormous - for example, I could plot an entire
multi-hundred page map book.

On the other hand, the ability to have PDFGraphics2D write directly to
the PDFStream should be fairly easy to implement. I'm looking into this

I did also uncover some bugs. Most prominently, PDFGraphics2D
instances spawned from others using createGraphics have their own
StringWriters and therefore anything rendered to them kind of
disappears off into space. I rewrote it so they share the same

In any case, I have a few major changes that may be useful. Are they,
and if so should I go ahead and see about getting CVS write access, or
does someone want to "sponsor" me or should I simply send a patch? I
have a feeling I'll be returning to the code in the future in any

Thanks. While I'm finding fop to be kind of a bear, it's still the
only real game in town for what I'm trying to do, and I'm getting some
great results - we just plotted half the state of new hampshire onto
a page the size of a bedsheet, and that's not easy to do without
banging your own postscript - add to that the ability to stick these
plots on nicely-formatted reports with all the power of FO too and it
makes my life a lot easier.


Paul Reavis                                      [EMAIL PROTECTED]
Design Lead
Partner Software, Inc.                        http://www.partnersoft.com

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