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+% \iffalse meta-comment
+%
+%% File: l3backend-basics.dtx
+%
+% Copyright (C) 2019-2024 The LaTeX Project
+%
+% It may be distributed and/or modified under the conditions of the
+% LaTeX Project Public License (LPPL), either version 1.3c of this
+% license or (at your option) any later version. The latest version
+% of this license is in the file
+%
+% https://www.latex-project.org/lppl.txt
+%
+% This file is part of the "l3backend bundle" (The Work in LPPL)
+% and all files in that bundle must be distributed together.
+%
+% -----------------------------------------------------------------------
+%
+% The development version of the bundle can be found at
+%
+% https://github.com/latex3/latex3
+%
+% for those people who are interested.
+%
+%<*driver>
+\documentclass[full,kernel]{l3doc}
+\begin{document}
+ \DocInput{\jobname.dtx}
+\end{document}
+%</driver>
+% \fi
+%
+% \title{^^A
+% The \pkg{l3backend-basics} module\\ Backend basics^^A
+% }
+%
+% \author{^^A
+% The \LaTeX{} Project\thanks
+% {^^A
+% E-mail:
+% \href{mailto:latex-team@latex-project.org}
+% {latex-team@latex-project.org}^^A
+% }^^A
+% }
+%
+% \date{Released 2024-04-11}
+%
+% \maketitle
+%
+% \begin{documentation}
+%
+% \end{documentation}
+%
+% \begin{implementation}
+%
+% \section{\pkg{l3backend-basics} implementation}
+%
+% \begin{macrocode}
+%<*package>
+% \end{macrocode}
+%
+% Whilst there is a reasonable amount of code overlap between backends,
+% it is much clearer to have the blocks more-or-less separated than run
+% in together and DocStripped out in parts. As such, most of the following
+% is set up on a per-backend basis, though there is some common code (again
+% given in blocks not interspersed with other material).
+%
+% All the file identifiers are up-front so that they come out in the right
+% place in the files.
+% \begin{macrocode}
+\ProvidesExplFile
+%<*dvipdfmx>
+ {l3backend-dvipdfmx.def}{2024-04-11}{}
+ {L3 backend support: dvipdfmx}
+%</dvipdfmx>
+%<*dvips>
+ {l3backend-dvips.def}{2024-04-11}{}
+ {L3 backend support: dvips}
+%</dvips>
+%<*dvisvgm>
+ {l3backend-dvisvgm.def}{2024-04-11}{}
+ {L3 backend support: dvisvgm}
+%</dvisvgm>
+%<*luatex>
+ {l3backend-luatex.def}{2024-04-11}{}
+ {L3 backend support: PDF output (LuaTeX)}
+%</luatex>
+%<*pdftex>
+ {l3backend-pdftex.def}{2024-04-11}{}
+ {L3 backend support: PDF output (pdfTeX)}
+%</pdftex>
+%<*xetex>
+ {l3backend-xetex.def}{2024-04-11}{}
+ {L3 backend support: XeTeX}
+%</xetex>
+% \end{macrocode}
+%
+% Check if the loaded kernel is at least enough to load this file.
+% The kernel date has to be at least equal to \cs{ExplBackendFileDate}
+% or later. If \cs{__kernel_dependency_version_check:Nn} doesn't
+% exist we're loading in an older kernel, so it's an error anyway.
+% With time, this test should vanish and only the dependency check
+% should remain.
+% \begin{macrocode}
+\cs_if_exist:NTF \__kernel_dependency_version_check:nn
+ {
+ \__kernel_dependency_version_check:nn {2023-10-10}
+%<dvipdfmx> {l3backend-dvipdfmx.def}
+%<dvips> {l3backend-dvips.def}
+%<dvisvgm> {l3backend-dvisvgm.def}
+%<luatex> {l3backend-luatex.def}
+%<pdftex> {l3backend-pdftex.def}
+%<xetex> {l3backend-xetex.def}
+ }
+ {
+ \cs_if_exist_use:cF { @latex@error } { \errmessage }
+ {
+ Mismatched~LaTeX~support~files~detected. \MessageBreak
+ Loading~aborted!
+ }
+ { \use:c { @ehd } }
+ \tex_endinput:D
+ }
+% \end{macrocode}
+%
+% The order of the backend code here is such that we get somewhat logical
+% outcomes in terms of code sharing whilst keeping things readable. (Trying to
+% mix all of the code by concept is almost unmanageable.) The key parts which
+% are shared are
+% \begin{itemize}
+% \item Color support is either \texttt{dvips}-like or \LuaTeX{}/pdfTeX{}-like.
+% \item \LuaTeX{}/pdfTeX{} and \texttt{dvipdfmx}/\XeTeX{} share drawing routines.
+% \item \XeTeX{} is the same as \texttt{dvipdfmx} other than image size
+% extraction so takes most of the same code.
+% \end{itemize}
+%
+% \begin{macro}
+% {
+% \__kernel_backend_literal:e,
+% \__kernel_backend_literal:n
+% }
+% The one shared function for all backends is access to the basic
+% \tn{special} primitive: it has slightly odd expansion behaviour
+% so a wrapper is provided.
+% \begin{macrocode}
+\cs_new_eq:NN \__kernel_backend_literal:e \tex_special:D
+\cs_new_protected:Npn \__kernel_backend_literal:n #1
+ { \__kernel_backend_literal:e { \exp_not:n {#1} } }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\__kernel_backend_first_shipout:n}
+% We need to write at first shipout in a few places. As we want to use the
+% most up-to-date method,
+% \begin{macrocode}
+\cs_if_exist:NTF \@ifl@t@r
+ {
+ \@ifl@t@r \fmtversion { 2020-10-01 }
+ {
+ \cs_new_protected:Npn \__kernel_backend_first_shipout:n #1
+ { \hook_gput_code:nnn { shipout / firstpage } { l3backend } {#1} }
+ }
+ { \cs_new_eq:NN \__kernel_backend_first_shipout:n \AtBeginDvi }
+ }
+ { \cs_new_eq:NN \__kernel_backend_first_shipout:n \use:n }
+% \end{macrocode}
+% \end{macro}
+%
+% \subsection{\texttt{dvips} backend}
+%
+% \begin{macrocode}
+%<*dvips>
+% \end{macrocode}
+%
+% \begin{macro}
+% {\__kernel_backend_literal_postscript:n, \__kernel_backend_literal_postscript:e}
+% Literal PostScript can be included using a few low-level formats. Here,
+% we use the form with no positioning: this is overall more convenient as
+% a wrapper. Note that this does require that where position is important,
+% an appropriate wrapper is included.
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_literal_postscript:n #1
+ { \__kernel_backend_literal:n { ps:: #1 } }
+\cs_generate_variant:Nn \__kernel_backend_literal_postscript:n { e }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\__kernel_backend_postscript:n, \__kernel_backend_postscript:e}
+% PostScript data that does have positioning, and also applying
+% a shift to |SDict| (which is not done automatically by
+% |ps:| or |ps::|, in contrast to |!| or |"|).
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_postscript:n #1
+ { \__kernel_backend_literal:n { ps: SDict ~ begin ~ #1 ~ end } }
+\cs_generate_variant:Nn \__kernel_backend_postscript:n { e }
+% \end{macrocode}
+% \end{macro}
+%
+% PostScript for the header: a small saving but makes the code clearer.
+% This is held until the start of shipout such that a document with no
+% actual output does not write anything.
+% \begin{macrocode}
+\bool_if:NT \g__kernel_backend_header_bool
+ {
+ \__kernel_backend_first_shipout:n
+ { \__kernel_backend_literal:n { header = l3backend-dvips.pro } }
+ }
+% \end{macrocode}
+%
+% \begin{macro}
+% {
+% \__kernel_backend_align_begin:,
+% \__kernel_backend_align_end:
+% }
+% In \texttt{dvips} there is no built-in saving of the current
+% position, and so some additional PostScript is required to set up the
+% transformation matrix and also to restore it afterwards. Notice the use
+% of the stack to save the current position \enquote{up front} and to
+% move back to it at the end of the process. Notice that the |[begin]|/^^A
+% |[end]| pair here mean that we can use a run of PostScript statements
+% in separate lines: not \emph{required} but does make the code and
+% output more clear.
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_align_begin:
+ {
+ \__kernel_backend_literal:n { ps::[begin] }
+ \__kernel_backend_literal_postscript:n { currentpoint }
+ \__kernel_backend_literal_postscript:n { currentpoint~translate }
+ }
+\cs_new_protected:Npn \__kernel_backend_align_end:
+ {
+ \__kernel_backend_literal_postscript:n { neg~exch~neg~exch~translate }
+ \__kernel_backend_literal:n { ps::[end] }
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\__kernel_backend_scope_begin:, \__kernel_backend_scope_end:}
+% Saving/restoring scope for general operations needs to be done with
+% \texttt{dvips} positioning (try without to see this!). Thus we need the
+% |ps:| version of the special here. As only the graphics state is ever
+% altered within this pairing, we use the lower-cost |g|-versions.
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_scope_begin:
+ { \__kernel_backend_literal:n { ps:gsave } }
+\cs_new_protected:Npn \__kernel_backend_scope_end:
+ { \__kernel_backend_literal:n { ps:grestore } }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macrocode}
+%</dvips>
+% \end{macrocode}
+%
+% \subsection{\LuaTeX{} and \pdfTeX{} backends}
+%
+% \begin{macrocode}
+%<*luatex|pdftex>
+% \end{macrocode}
+%
+% Both \LuaTeX{} and \pdfTeX{} write PDFs directly rather than via an
+% intermediate file. Although there are similarities, the move of \LuaTeX{}
+% to have more code in Lua means we create two independent files using
+% shared DocStrip code.
+%
+% \begin{macro}{\__kernel_backend_literal_pdf:n, \__kernel_backend_literal_pdf:e}
+% This is equivalent to \verb|\special{pdf:}| but the engine can
+% track it. Without the \texttt{direct} keyword everything is kept in
+% sync: the transformation matrix is set to the current point automatically.
+% Note that this is still inside the text (\texttt{BT} \dots \texttt{ET}
+% block).
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_literal_pdf:n #1
+ {
+%<*luatex>
+ \tex_pdfextension:D literal
+%</luatex>
+%<*pdftex>
+ \tex_pdfliteral:D
+%</pdftex>
+ { \exp_not:n {#1} }
+ }
+\cs_generate_variant:Nn \__kernel_backend_literal_pdf:n { e }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\__kernel_backend_literal_page:n, \__kernel_backend_literal_page:e}
+% Page literals are pretty simple. To avoid an expansion, we write out
+% by hand.
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_literal_page:n #1
+ {
+%<*luatex>
+ \tex_pdfextension:D literal ~
+%</luatex>
+%<*pdftex>
+ \tex_pdfliteral:D
+%</pdftex>
+ page { \exp_not:n {#1} }
+ }
+\cs_new_protected:Npn \__kernel_backend_literal_page:e #1
+ {
+%<*luatex>
+ \tex_pdfextension:D literal ~
+%</luatex>
+%<*pdftex>
+ \tex_pdfliteral:D
+%</pdftex>
+ page {#1}
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\__kernel_backend_scope_begin:, \__kernel_backend_scope_end:}
+% Higher-level interfaces for saving and restoring the graphic state.
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_scope_begin:
+ {
+%<*luatex>
+ \tex_pdfextension:D save \scan_stop:
+%</luatex>
+%<*pdftex>
+ \tex_pdfsave:D
+%</pdftex>
+ }
+\cs_new_protected:Npn \__kernel_backend_scope_end:
+ {
+%<*luatex>
+ \tex_pdfextension:D restore \scan_stop:
+%</luatex>
+%<*pdftex>
+ \tex_pdfrestore:D
+%</pdftex>
+ }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\__kernel_backend_matrix:n, \__kernel_backend_matrix:e}
+% Here the appropriate function is set up to insert an affine matrix
+% into the PDF. With \pdfTeX{} and \LuaTeX{} in direct PDF output mode there
+% is a primitive for this, which only needs the rotation/scaling/skew part.
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_matrix:n #1
+ {
+%<*luatex>
+ \tex_pdfextension:D setmatrix
+%</luatex>
+%<*pdftex>
+ \tex_pdfsetmatrix:D
+%</pdftex>
+ { \exp_not:n {#1} }
+ }
+\cs_generate_variant:Nn \__kernel_backend_matrix:n { e }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macrocode}
+%</luatex|pdftex>
+% \end{macrocode}
+%
+% \subsection{\texttt{dvipdfmx} backend}
+%
+% \begin{macrocode}
+%<*dvipdfmx|xetex>
+% \end{macrocode}
+%
+% The \texttt{dvipdfmx} shares code with the PDF mode one (using the common
+% section to this file) but also with \XeTeX{}. The latter is close
+% to identical to \texttt{dvipdfmx} and so all of the code here is extracted
+% for both backends, with some \texttt{clean up} for \XeTeX{} as
+% required.
+%
+% \begin{macro}{\__kernel_backend_literal_pdf:n, \__kernel_backend_literal_pdf:e}
+% Undocumented but equivalent to \pdfTeX{}'s |literal| keyword. It's similar to
+% be not the same as the documented |contents| keyword as that adds a |q|/|Q|
+% pair.
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_literal_pdf:n #1
+ { \__kernel_backend_literal:n { pdf:literal~ #1 } }
+\cs_generate_variant:Nn \__kernel_backend_literal_pdf:n { e }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\__kernel_backend_literal_page:n}
+% Whilst the manual says this is like |literal direct| in \pdfTeX{},
+% it closes the |BT| block!
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_literal_page:n #1
+ { \__kernel_backend_literal:n { pdf:literal~direct~ #1 } }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\__kernel_backend_scope_begin:, \__kernel_backend_scope_end:}
+% Scoping is done using the backend-specific specials. We use the versions
+% originally from \texttt{xdvidfpmx} (\texttt{x:}) as these are well-tested
+% \enquote{in the wild}.
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_scope_begin:
+ { \__kernel_backend_literal:n { x:gsave } }
+\cs_new_protected:Npn \__kernel_backend_scope_end:
+ { \__kernel_backend_literal:n { x:grestore } }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{macrocode}
+%</dvipdfmx|xetex>
+% \end{macrocode}
+%
+% \subsection{\texttt{dvisvgm} backend}
+%
+% \begin{macrocode}
+%<*dvisvgm>
+% \end{macrocode}
+%
+% \begin{macro}{\__kernel_backend_literal_svg:n, \__kernel_backend_literal_svg:e}
+% Unlike the other backends, the requirements for making SVG files mean
+% that we can't conveniently transform all operations to the current point.
+% That makes life a bit more tricky later as that needs to be accounted for.
+% A new line is added after each call to help to keep the output readable
+% for debugging.
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_literal_svg:n #1
+ { \__kernel_backend_literal:n { dvisvgm:raw~ #1 { ?nl } } }
+\cs_generate_variant:Nn \__kernel_backend_literal_svg:n { e }
+% \end{macrocode}
+% \end{macro}
+%
+% \begin{variable}{\g__kernel_backend_scope_int, \l__kernel_backend_scope_int}
+% In SVG, we need to track scope nesting as properties attach to scopes; that
+% requires a pair of \texttt{int} registers.
+% \begin{macrocode}
+\int_new:N \g__kernel_backend_scope_int
+\int_new:N \l__kernel_backend_scope_int
+% \end{macrocode}
+% \end{variable}
+%
+% \begin{macro}{\__kernel_backend_scope_begin:, \__kernel_backend_scope_end:}
+% \begin{macro}{\__kernel_backend_scope_begin:n, \__kernel_backend_scope_begin:e}
+% \begin{macro}{\__kernel_backend_scope:n, \__kernel_backend_scope:e}
+% In SVG, the need to attach concepts to a scope means we need to be sure we
+% will close all of the open scopes. That is easiest done if we only need
+% an outer \enquote{wrapper} \texttt{begin}/\texttt{end} pair, and within
+% that we apply operations as a simple scoped statements. To keep down the
+% non-productive groups, we also have a \texttt{begin} version that does take
+% an argument.
+% \begin{macrocode}
+\cs_new_protected:Npn \__kernel_backend_scope_begin:
+ {
+ \__kernel_backend_literal_svg:n { <g> }
+ \int_set_eq:NN
+ \l__kernel_backend_scope_int
+ \g__kernel_backend_scope_int
+ \group_begin:
+ \int_gset:Nn \g__kernel_backend_scope_int { 1 }
+ }
+\cs_new_protected:Npn \__kernel_backend_scope_end:
+ {
+ \prg_replicate:nn
+ { \g__kernel_backend_scope_int }
+ { \__kernel_backend_literal_svg:n { </g> } }
+ \group_end:
+ \int_gset_eq:NN
+ \g__kernel_backend_scope_int
+ \l__kernel_backend_scope_int
+ }
+\cs_new_protected:Npn \__kernel_backend_scope_begin:n #1
+ {
+ \__kernel_backend_literal_svg:n { <g ~ #1 > }
+ \int_set_eq:NN
+ \l__kernel_backend_scope_int
+ \g__kernel_backend_scope_int
+ \group_begin:
+ \int_gset:Nn \g__kernel_backend_scope_int { 1 }
+ }
+\cs_generate_variant:Nn \__kernel_backend_scope_begin:n { e }
+\cs_new_protected:Npn \__kernel_backend_scope:n #1
+ {
+ \__kernel_backend_literal_svg:n { <g ~ #1 > }
+ \int_gincr:N \g__kernel_backend_scope_int
+ }
+\cs_generate_variant:Nn \__kernel_backend_scope:n { e }
+% \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macrocode}
+%</dvisvgm>
+% \end{macrocode}
+%
+% \begin{macrocode}
+%</package>
+% \end{macrocode}
+%
+% \end{implementation}
+%
+% \PrintIndex