On Fri, Jul 4, 2014 at 12:37 AM, Sanjoy Mahajan <sanjoy@mit.edu> wrote:

> > context --make does a --generate so you can skip that and the luatools
> > run is not needed either (selfupdate is seldom needed too)
>
> So 'context --make' is all one needs?  I'll update the wiki.
>
> > we get a .5pt height difference somewhere (nothing else different in a
> > trace) ... smells like a luatex bug (testing that now)
>
> That is my suspicion as well.  But I couldn't reproduce it with plain
> luatex.  Though maybe I needed to use equation numbers, however that is
> done in plain tex (the context run doesn't show the problem without the
> \placeformula).
>
> I suspect some internal state is getting slightly corrupted and getting
> progressively worse with the 30,000 repetitions.
>
> I've been finding many unexplained 0.5pt or so differences, which may be
> related to the underbrace problem.  The context, so to speak, is that I
> am putting in the last edits to the book, after having gone through and
> checked every page many times.  So I want to ensure that none of the
> small changes has a big effect, but I don't want to check every page
> again (or I'll vomit).
>
> Thus, I run my compare-pdfs.sh script on the previous and the latest
> pdf. It renders each page to a B/W png (using mupdf) and then compares
> corresponding pages using 'compare' (one of the ImageMagick tools).  Any
> differing pixels are in red, and the shared pixels are in very light
> gray.  Then all the pages with enough differences are viewed with 'feh',
> in order of most-to-least differences.  And I check that nothing major
> has changed.
>
> What I keep finding is that pages long after where I make a small change
> somehow get changed, with roughly one-pixel shifts to parts of the page.
> I'm attaching an example pixel diff.  It shows changes on p.72 of the
> mss.  However, the only change to the source code was on p.58 (and was
> designed not to change any page breaks, which it didn't).  That same
> page (p.72) often gets similar changes with all kinds of small changes.
>
> [Note to me: In case I need to recreate the source for debugging
> purposes, it's the change from rev 41ff54 to 2467d5]
>
> In case the script is useful to others (earlier versions are in the
> contexttest repository somewhere), I am attaching it.  I use it as
> follows with a bash command line.  (The awk in the pipeline makes sure
> that only pages with some difference make it to the viewer.)
>
> DPI=72 compare-pdfs.sh old.pdf new.pdf | tee book-print.compare72dpi | awk
> '{if (($3 > 0.02)) print;}' | sort -nr -k3 | awk '{print $1}' | xargs -r feh
>
> Thank you for the script.
Under linux you can also try diffpdf
$> aptitude search diffpdf
i   diffpdf
                                                        - compare two PDF
files textually or visually

p   diffpdf:i386
                                                         - compare two PDF
files textually or visually


-- 
luigi