From: Jonathan Corbet <corbet@lwn.net>
Date: Thu, 10 Feb 2022 00:29:05 +0000 (-0700)
Subject: Merge branch 'pdf-conversion' into docs-next
X-Git-Tag: v6.6.17~7841^2~65
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=f647de4b02dcb1815fb3019f86a001a681daf0a1;p=platform%2Fkernel%2Flinux-rpi.git

Merge branch 'pdf-conversion' into docs-next

PDF-generation improvements from Akira Yokasawa; Akira says:

This patch set improves conversions of DOT -> PDF and SVG -> PDF
for PDF docs.

* DOT -> PDF conversion

Current scheme uses "dot -Tpdf" (of graphviz).

Cons:
  - openSUSE's dot(1) does not support -Tpdf.
  - Other distro's dot(1) generates PDFs with unnecessarily wide
    margins for inclusion into LaTeX docs.

Patch 1/4 changes the route to the following two steps:

  1. DOT -> SVG by "dot -Tsvg"
  2. SVG -> PDF by "rsvg-convert -f pdf" with fallback to convert(1)

Pros:
  - Improved portability across distros
  - Less space around graphs in final PDF documents

Con:
  - On systems without rsvg-convert, generated PDF will be of raster
    image.

Patch 2/4 avoids raster-image PDF by using "dot -Tpdf" on systems where
the option is available.

* SVG -> PDF conversion

Current scheme uses convert(1) (of ImageMagick)

Cons:
  - Generated PDFs are of raster image.  Some of them look blurry.
  - Raster images tend to be large in size.
  - convert(1) delegates SVG decoding to rsvg-convert(1).
    It doesn't cover full range of Inkscape-specific SVG features
    and fails to convert some of SVG figures properly.

Improper conversions are observed with SVGs listed below (incomplete,
conversion quality depends on the version of rsvg-convert):
  - Documentation/userspace-api/media/v4l/selection.svg
  - Documentation/userspace-api/media/v4l/vbi_525.svg
  - Documentation/userspace-api/media/v4l/vbi_625.svg
  - Documentation/userspace-api/media/v4l/vbi_hsync.svg
  - Documentation/admin-guide/blockdev/drbd/DRBD-8.3-data-packets.svg
  - Documentation/admin-guide/blockdev/drbd/DRBD-data-packages.svg

If you have Inkscape installed as well, convert(1) delegates SVG
decoding to inkscape(1) rather than to rsvg-convert(1) and SVGs listed
above can be rendered properly.

So if Inkscape is required for converting those SVGs properly, why not
use it directly in the first place?

Patches 3/4 and 4/4 add code to utilize inkscape(1) for SVG -> PDF
conversion when it is available.  They don't modify any existing
requirements for kernel-doc.

Patch 3/4 adds the alternative route of SVG -> PDF conversion by
inkscape(1).
Patch 4/4 delegates warning messages from inkscape(1) to kernellog.verbose
as they are likely harmless in command-line uses.

Pros:
  - Generated PDFs are of vector graphics.
  - Vector graphics tends to be smaller in size and looks nicer when
    zoomed in.
  - SVGs drawn by Inkscape are fully supported.

On systems without Inkscape, no regression is expected by these two
patches.
---

f647de4b02dcb1815fb3019f86a001a681daf0a1