[pdf-devel] Predictor filter

[Ed]

Hello

The GNU high priority projects list talked me into trying to
contribute to this again(!) It's not the easiest thing to do!

Anyway I made a start on porting the predictor filters to the new API.
I have the encoder "done" and I could do the decoder fairly easily I
think. The problem is I have no idea how to test this?

I can't persuade bzr to give me any kind of useful history information
(i.e. bzr blame tells me revisions which it then appears unable to
diff reliably). As far as I can tell, there were no test cases for the
predictor stuff before. There are certainly none now, commented out or
otherwise (according to "find -name *.c | xargs grep -i pred").

How do I find out if it works? I re-installed it in the pdf-filter
application, but what can I do with that application? Since it works
by scanlines, and has a large range of formats, typing in test data by
hand to standard input would be both quite challenging and probably
unproductive.

Additionally, is there any documentation for the architecture (beyond
high level fluff?). I copied the implementation of the LZW filter, but
I couldn't work out what the finish_p parameter meant in the apply
function.. Is this some cue to write a trailer if needed? I ignored it
on the basis that the predictor stuff hadn't needed such a flag
before, but this was just a guess.

I appreciate this is a different kind of software project from the
ones I usually contribute to, so apologies if this steps over some
unwritten rules of etiquette.

Ed