Title: A day as an OpenBSD developer
Author: Solène
Date: 19 February 2020
Tags: life openbsd
Description:
This is a little story that happened a few days ago, it explains well
how I
usually get involved into ports in OpenBSD.
## 1 - Lurking into ports/graphics/
At first, I was looking in various ports there are in the graphics
category,
searching for an image editor that would run correctly on my offline
laptop.
Grafx2 is laggy when using the zoom mode and GIMP won't run, so I just
open
ports randomly to read their pkg/DESCR file.
This way, I often find gems I reuse later, sometimes I have less luck
and I
only tried 20 ports which are useless to me. It happens I find issues
in ports
looking randomly like this...
## 2 - Find the port « comix »
Then, the second or third port I look at is « comix », here is the
DESCR file.
Comix is a user-friendly, customizable image viewer. It is
specifically
designed to handle comic books, but also serves as a generic
viewer. It
reads images in ZIP, RAR or tar archives (also gzip or bzip2
compressed)
as well as plain image files.
That looked awesome, I have lot of books as PDF I want to read but it's
not
convenient in a "normal" PDF reader, so maybe comix would help!
## 3 - Using comix
Once comix was compiled (a mix of python and gtk), I start it and I get
errors
opening PDFs... I start it again from console, and in the output I get
the
explanation that PDF files are not usable in comix.
Then I read about the CBZ or CBT files, they are archives (zip or tar)
containing pictures, definitely not what a PDF is.
## 4 - mcomix > comix
After a few searches on the Internet, I find that comix last release is
from
2009 and it never supported PDF, so nothing wrong here, but I also
found comix
had a fork named mcomix.
mcomix forked a long time ago from comix to fix issues and add support
for new
features (like PDF support), while last release is from 2016, it works
and
still receive commits (last is from late 2019). I'm going for using
comix!
## 5 - Installing mcomix from ports
Best way to install a program on OpenBSD is to make a port, so it's
correctly
packaged, can be deinstalled and submit to ports@ mailing list later.
I did copy comix folder into mcomix, use a brain dead sed command to
replace all
occurrence of comix by mcomix, and it mostly worked! I won't explain
little
details, but I got mcomix to work within a few minutes and I was quite
happy!
Fun fact is that **comix** port Makefile was mentioning mcomix as a
suggestion
for upgrade.
## 6 - Enjoying a CBR reader
With mcomix installed, I was able to read some PDF, it was a good
experience
and I was pretty happy with it. I've spent a few hours reading, a few
moments
after mcomix was installed.
## 7 - mcomix works but not all the time
After reading 2 longs PDFs, I got issues with the third, some pages
were not
rendered and not displayed. After digging this issue a bit, I found
about
mcomix internals. Reading PDF is done by rendering every page of the
PDF using
**mutool** binary from **mupdf** software, this is quite CPU intensive,
and for
some reason in mcomix the command execution fails while I can do the
exact same
command a hundred time with no failure. Worse, the issue is not
reproducible in
mcomix, sometimes some pages will fail to be rendered, sometimes not!
## 8 - Time to debug some python
I really want to read those PDF so I take my favorite editor and start
debugging some python, adding more debug output (mcomix has a -W
parameter
to enable debug output, which is very nice), to try to understand why
it
fails at getting output of a working command.
Sadly, my python foo is too low and I wasn't able to pinpoint the
issue. I just
found it fail, sometimes, but I wasn't able to understand why.
## 9 - mcomix on PowerPC
While mcomix is clunky with PDF, I wanted to check if it was working on
PowerPC, it took some times to get all the dependencies installed on my
old
computer but finally I got mcomix displayed on the screen... and dying
on PDF
loading! Crash seems related to GTK and I don't want to touch that,
nobody will
want to patch GTK for that anyway so I've lost hope there.
## 10 - Looking for alternative
Once I knew about mcomix, I was able to search the Internet for
alternatives of
it and also CBR readers. A program named **zathura** seems well known
here and
we have it in the OpenBSD ports tree.
Weird thing is that it comes with two different PDF plugins, one named
**mupdf** and the other one **poppler**. I did try quickly on my amd64
machine
and zathura was working.
## 11 - Zathura on PowerPC
As Zathura was working nice on my main computer, I installed it on the
PowerPC,
first with the **poppler** plugin, I was able to view PDF, but
installing this
plugin did pull so many packages dependencies it was a bit sad. I
deinstalled
the poppler PDF plugin and installed mupdf plugin.
I opened a PDF and... error. I tried again but starting zathura from
the
terminal, and I got the message that PDF is not a supported format,
with a lot
of lines related to mupdf.so file not being usable. The mupdf plugin
work on
amd64 but is not usable on powerpc, this is a bug I need to report, I
don't
understand why this issue happens but it's here.
## 12 - Back to square one
It seems that reading PDF is a mess, so why couldn't I convert the PDF
to CBT
files and then use any CBT reader out there and not having to deal with
that
PDF madness!!
## 13 - Use big calibre for the job
I have found on the Internet that Calibre is the most used tool to
convert a
PDF into CBT files (or into something else but I don't really care
here). I
installed calibre, which is not lightweight, started it and wanted to
change
the default library path, the software did hang when it displayed the
file
dialog. This won't stop me, I restart calibre and keep the default
path, I
click on « Add a book » and then it hang again on file dialog. I did
report
this issue on ports@ mailing list, but it didn't solve the issue and
this mean
calibre is not usable.
## 14 - Using the command line
After all, CBT files are images in a tar file, it should be easy to
reproduce
the mcomix process involving mutool to render pictures and make a tar
of that.
**IT WORKED.**
I found two ways to proceed, one is extremely fast but may not make
pages in
the correct order, the second requires CPU time.
#### Making CBT files - easiest process
The first way is super easy, it requires **mutool** (from mupdf
package) and it
will extract the pictures from the PDF, given it's not a vector PDF,
not sure
what would happen on those. The issue is that in the PDF, the embedded
pictures
have a name (which is a number from the few examples I found), and it's
not
necessarily in the correct order. I guess this depend how the PDF is
made.
$ mutool extract The_PDF_file.pdf
$ tar cvf The_PDF_file.tar *jpg
That's all you need to have your CBT file. In my PDF there was jpg
files in it,
but it may be png in others, I'm not sure.
#### Making CBT files - safest process (slow)
The other way of making pictures out of the PDF is the one used in
mcomix, call
**mutool** for rendering each page as a PNG file using width/height/DPI
you
want. That's the tricky part, you may not want to produce pictures with
larger
resolution than the original pictures (and mutool won't automatically
help you
for this) because you won't get any benefit. This is the same for the
DPI. I
think this could be done automatically using a correct script checking
each PDF
page resolution and using mutool to render the page with the exact same
resolution.
As a rule of thumb, it seems that rendering using the same width as
your screen
is enough to produce picture of the correct size. If you use large
values, it's
not really an issue, but it will create bigger files and take more time
for
rendering.
$ mutool draw -w 1920 -o page%d.png The_PDF_file.pdf
$ tar cvf The_PDF_file.tar page*.png
You will get PNG files for each page, correctly numbered, with a width
of 1920
pixels. Note that instead of tar, you can use zip to create a zip file.
## 15 - Finally reading books again
After all this LONG process, I was finally able to read my PDF with any
CBR
reader out there (even on phone), and once the process is done, it uses
no cpu
for viewing files at the opposite of mcomix rendering all the pages
when you
open a file.
I have to use zathura on PowerPC, even if I like it less due to the
continuous
pages display (can't be turned off), but mcomix definitely work great
when not
dealing with PDF. I'm still unsure it's worth committing mcomix to the
ports
tree if it fails randomly on random pages with PDF.
## 16 - Being an open source activist is exhausting
All I wanted was to read a PDF book with a warm cup of tea at hand.
It ended into learning new things, debugging code, making ports,
submitting
bugs and writing a story about all of this.