Message-ID: <20161109102750.5cee0d70@vento.lan>
Date:   Wed, 9 Nov 2016 10:27:50 -0200
From:   Mauro Carvalho Chehab <mchehab@...pensource.com>
To:     Jani Nikula <jani.nikula@...el.com>
Cc:     Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-doc@...r.kernel.org,
        ksummit-discuss@...ts.linuxfoundation.org
Subject: Re: Including images on Sphinx documents

Em Mon, 07 Nov 2016 12:53:55 +0200
Jani Nikula <jani.nikula@...el.com> escreveu:

> On Mon, 07 Nov 2016, Mauro Carvalho Chehab <mchehab@...pensource.com> wrote:
> > Hi Jon,
> >
> > I'm trying to sort out the next steps to do after KS, with regards to
> > images included on RST files.
> >
> > The issue is that Sphinx image support highly depends on the output
> > format. Also, despite TexLive support for svg and png images[1], Sphinx
> > doesn't produce the right LaTeX commands to use svg[2]. On my tests
> > with PNG on my notebook, it also didn't seem to do the right thing for
> > PNG either. So, it seems that the only safe way to support images is
> > to convert all of them to PDF for latex/pdf build.
> >
> > [1] On Fedora, via texlive-dvipng and texlive-svg
> > [2] https://github.com/sphinx-doc/sphinx/issues/1907
> >
> > As far as I understand from KS, two decisions was taken:
> >
> > - We're not adding a sphinx extension to run generic commands;
> > - The PDF images should be build in runtime from their source files
> >   (either svg or bitmap), and not ship anymore the corresponding
> >   PDF files generated from its source.
> >
> > As you know, we use several images at the media documentation:
> > 	https://www.kernel.org/doc/html/latest/_images/
> >
> > Those images are tightly coupled with the explanation texts. So,
> > maintaining them away from the documentation is not an option.
> >
> > I was originally thinking that adding a graphviz extension would solve the
> > issue, but, in fact, most of the images aren't diagrams. Instead, there are 
> > several ones with images showing the result of passing certain parameters to
> > the ioctls, explaining things like scale and cropping and how bytes are
> > packed on some image formats.
> >
> > Linus proposed to call some image conversion tool like ImageMagick or
> > inkscape to convert them to PDF when building the pdfdocs or latexdocs
> > target at Makefile, but there's an issue with that: Sphinx doesn't read
> > files from Documentation/output, and writing them directly at the
> > source dir would be against what it is expected when the "O=" argument
> > is passed to make. 
> >
> > So, we have a few alternatives:
> >
> > 1) copy (or symlink) all rst files to Documentation/output (or to the
> >    build dir specified via O= directive) and generate the *.pdf there,
> >    and produce those converted images via Makefile.;
> >
> > 2) add an Sphinx extension that would internally call ImageMagick and/or
> >    inkscape to convert the bitmap;
> >
> > 3) if possible, add an extension to trick Sphinx for it to consider the 
> >    output dir as a source dir too.  
> 
> Looking at the available extensions, and the images to be displayed,
> seems to me making svg work, somehow, is the right approach. (As opposed
> to trying to represent the images in graphviz or whatnot.)

I guess answered this one already, but it got lost somehow...

The problem is not just with svg. Sphinx also do the wrong thing with
PNG, despite apparently generating the right LaTeX image include command.

> IIUC texlive supports displaying svg directly, but the problem is that
> Sphinx produces bad latex for that. Can we make it work by manually
> writing the latex? If yes, we wouldn't need to use an external tool to
> convert the svg to something else, but rather fix the latex. Thus:
> 
> 4a) See if this works:
> 
> .. only:: html
> 
>    .. image:: foo.svg

We're currently using .. figure:: instead, as it allow optional caption
and legend, but I got the idea.

> .. raw:: latex
> 
>    <the correct latex commands required to display foo.svg>

That is a horrible hack, and will lose other attributes at
image:: (or figure::), like :align:

Also, it won't solve, as the images will need to be copied to the
build dir via Makefile, as Spinx only copies the images it recognizes.

So, in practice, the only difference is that Makefile would be calling
"cp" instead of "convert", plus we'll have to hack all ReST sources.

> 4b) Add a directive extension to make the above happen automatically.

If doable, I agree that this is the best solution. Any volunteers to write
such extension?

> Of course, the correct fix is to have this fixed in upstream Sphinx, but
> as a workaround an extension doing the above seems plausible, and not
> too much effort - provided that we can make the raw latex work.

Yeah, fixing it on Sphinx upstream would be the best, but we'll still
need to maintain the workaround for a while for the unpatched versions
of Sphinx.

Thanks,
Mauro

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