Re: Missing items to make Cairo ready

[Luca Fascione]

On Sat, Jan 7, 2023 at 10:06 PM Jean Abou Samra <jean@abou-samra.fr> wrote:

> the advantage of dropping \epsfile
> and \postscript isn't big either, as their Cairo implementation is not
> complicated and can largely share code with the implementation of
> other image formats
>

Hang on. I don't think this is correct: I had understood that on the
postscript backend
the postscript in the arguments to the two commands above goes verbatim
into the output file, doesn't it?
In particular this means the PDF contains vector images when the input is
things like paths and such stuff,
or scalable fonts, possibly together with their definitions when that's the
case with the input.
Comparing this to Cairo where an external renderer is invoked to turn them
into raster images and
then embeds those into a PDF, which would make it all non-scalable.

This is all assuming that \postscript is not passing through actual code
that modifies the state of the postscript interpreter
which the new system can't even do (like you could have a \postscript
command to set up a dictionary, later in your file another to
set up some state, and further to read such state and generate text, for
example you could generate page numbers like this if you wanted, or
maybe back references (not that it would be a smart thing to do, but you
could). I don't quite see how running this through ghostscript a bit at a
time
would achieve the right result.

So it seems to me \postscript and \epsfile can only do exactly what they
currently do if the emitted file is postscript.

In saying this, I think that them not working in other output modes is
just fine (as long as the use has a way to check what output mode is
currently running).
I'm thinking if we had similar mechanism for direct ingestion of XML in SVG
mode (I do realize it's a much weirder thing to make available in
practice), and equivalently
direct emission of PDF, and each just did something useful in the
corresponding mode, it would be just fine.

The TeX people are in this situation, and it doesn't seem to bother users
much (because it's largely hidden by the packages, arguably, at least in
LaTeX).

L


-- 
Luca Fascione