Re: Add `-dgs-neverembed-fonts` option (issue 312970043 by address@hidden)

[trueroad]

> > I am happy to help with the documentation if language is a
difficulty to
> > describe, but fundamentally what is the purpose of this command and
why, as a
> > user, would I want to use (and perhaps not to use it?).

> I leave a detailed answer to Masamichi-san :-)

This option is very useful when `lilypond-book` invokes `lilypond`
command.
You will not use it when you directly invoke `lilypond` command.

When you create a PDF document using `lilypond-book` you may include
many LilyPond snippets in the main PDF file.
Each snippet intermediate file is a small PDF file which is generated by
`lilypond` command.
Each of the small PDF files use the same fonts, Emmentaler and TeX Gyre.

`lilypond-book` invokes `lilypond` command for generating each snippet
intermediate small PDF file.
Then, it invokes TeX (pdfTeX, XeTeX, LuaTex etc.) for generating main
PDF which includes the small PDF files.

If the small PDF files contain embedded font subsets (it is the default
of `lilypond`), the TeX system includes them as-is in the main PDF.
As a result, several subsets of the same font are embedded in the main
PDF.
It is not possible to remove the duplicates since they are different
subsets.
This vastly increases the size of the main PDF file.

On the other hand, if the small PDF files contain embedded full font
sets (by the LilyPond `--bigpdfs` option), the TeX system also includes
all of them in the main PDF.
This time, the main PDF contains duplicates of the same full sets of
fonts.
Therefore, Ghostscript can remove the duplicates.
This may considerably reduce the main PDF-file's size.

Finally, if the small PDF files contain some fonts that are not embedded
(by this option `-dgs-neverembed-fonts`), the TeX system outputs the
main PDF file with some fonts missing.
In this case, Ghostscript can embed the necessary fonts.
It can significantly reduce the required disk size.

Unfortunately, the never embed method does not work fine for TrueType
fonts.
http://lists.gnu.org/archive/html/lilypond-devel/2016-10/msg00080.html

So this option embeds TrueType fonts but does not embed Type 1 fonts and
OpenType/CFF fonts.


https://codereview.appspot.com/312970043/