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Re: Using/requiring Cairo

From: David Kastrup
Subject: Re: Using/requiring Cairo
Date: Sat, 24 Jun 2017 20:52:37 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux)

address@hidden writes:

> David Kastrup:
>> address@hidden writes:
>> > Han-Wen Nienhuys:
>> >> On Sat, Jun 24, 2017 at 12:43 PM, David Kastrup <address@hidden> wrote:
> ...
>> > If no one else like to care for postscript, I can step in to handle it.
>> I don't know what that means.
> It's like english, I am willing to take care of something related to
> the programming language PostScript, so we don't need to convert to
> cairo.

"taking care of PostScript" is not related to converting LilyPond's
graphics internals to Cairo since LilyPond's graphics internals are not
written in PostScript.

>>  My proposed migration plan would not have
>> changed the PostScript backend at first, but it certainly would have
>> been slated for eventual retirement.
> And I more or less said that I didn't like the retirement thing.

The TeX backend processing was retired when LilyPond was changed from
version 1 to 2 and learnt to write its own PostScript.

At the current point of time, high amounts of work are invested into the
font processing in PostScript, dealing with subletting, with document
merging and so on.  When processing in general will get moved to Cairo,
there will eventually be a state where

a) the backends are organized differently
b) ongoing work is generally invested only in the Cairo backend path

That means that anybody willing to "care for PostScript" in the sense of
producing the same kind of PostScript output as now will have a whole
lot more work on his hand than just basic maintenance of existing code
since he has to replace all the experts currently invested with the
finer points of PostScript intended for PDF conversion while they move

> If you already decided to switch to cairo, then fine, tell us so we
> can stop this discussion.

Shrug.  I don't have any capacity to decide anything.

>> > I use PS as the final format.  Cairo can export to postscript but it's
>> > PS is not nice to read, lilypond PS is much better in that respect.
>> PostScript is not intended to be human-readable rather than
>> human-writable and streamable,
> PostScript is a programming language suited for printing and other
> things. Why youldn't I like to have that readable and understandable
> like any other code ?

Because it is employed as an intermediate format not intended for human
consumption and manipulation?  It's similar to the role of LilyPond in a
Denemo workflow.  It's nice for debugging when it's somewhat readable,
but the files created in it are ephemeral.  Editing them does not make
sense.  PDF has by far outclassed PostScript in usage _because_ it does
no longer bother being readable and writable by humans rather than

>> two characteristics PDF no longer cares about in return for better
>> computer-readability and processability.
> PDFReference16.pdf is 1236 pages long and is no easy read.
> The first version of the green/blue/red book was good at getting you
> started at postscript, do you have any similar doc to get you started
> at pdf ?

You are not supposed to get started at writing PDF.  Instead the PDF
gets written by programs.  You are fine with letting your PDF be written
by Ghostscript rather than LilyPond and not looking at it.  What is the
difference with PostScript in your workflow that makes it different?

> I have tried to find some free lib to use to read pdf's, if you know
> of one please tell me, preferable for perl.


> Currently I'm using "pdftohtml --xml", but there is a few things
> missing with that solution.
> I know about poppler, citing:
> //
>  Documentation
>  There is currently very little documentation. 
> //
> Soo, the computer-readability is a nice goal, but not so much
> attained.

Well, there isn't a free lib for reading PostScript, is there?

I mean, how much is ps2pdf documented?

> ...
>>  That makes it a lot less likely to be
>> suitable for mechanical processing (like using "Tailor") than PostScript
>> generated from a general-purpose representation with commonly used
>> toolkits.
> ...
> Ok, stop bullshitting. Both ps and pdf are a "general-purpose 
> representaion", both have "commonly used toolkits", and both are 
> suitable for "mechanical processing" (by e.g. a printer).
> What is "Tailor" in this context, I don't understand what you mean by 
> that ?


Basically the principal reason NeXT computers were kept around (NeXT was
what Steven Jobs was working on while being laid off from Apple).

PDF editing was more dependable.

David Kastrup

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