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l3backend-basics.dtx
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l3backend-basics.dtx
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% \iffalse meta-comment
%
%% File: l3backend-basics.dtx
%
% Copyright (C) 2019-2021 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 \textsf{l3backend-basics} package\\ 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 2021-02-06}
%
% \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}{2021-02-06}{}
{L3 backend support: dvipdfmx}
%</dvipdfmx>
%<*dvips>
{l3backend-dvips.def}{2021-02-06}{}
{L3 backend support: dvips}
%</dvips>
%<*dvisvgm>
{l3backend-dvisvgm.def}{2021-02-06}{}
{L3 backend support: dvisvgm}
%</dvisvgm>
%<*luatex>
{l3backend-luatex.def}{2021-02-06}{}
{L3 backend support: PDF output (LuaTeX)}
%</luatex>
%<*pdftex>
{l3backend-pdftex.def}{2021-02-06}{}
{L3 backend support: PDF output (pdfTeX)}
%</pdftex>
%<*xetex>
{l3backend-xetex.def}{2021-02-06}{}
{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 {2020-09-01}
%<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,
% \__kernel_backend_literal:x
% }
% 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} } }
\cs_generate_variant:Nn \__kernel_backend_literal:n { x }
% \end{macrocode}
% \end{macro}
%
% \subsection{\texttt{dvips} backend}
%
% \begin{macrocode}
%<*dvips>
% \end{macrocode}
%
% \begin{macro}
% {\__kernel_backend_literal_postscript:n, \__kernel_backend_literal_postscript:x}
% 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 { x }
% \end{macrocode}
% \end{macro}
%
% \begin{macro}{\__kernel_backend_postscript:n, \__kernel_backend_postscript:x}
% 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 { x }
% \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
{
\cs_if_exist:NTF \AtBeginDvi
{ \AtBeginDvi }
{ \use: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:x}
% 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 { x }
% \end{macrocode}
% \end{macro}
%
% \begin{macro}{\__kernel_backend_literal_page:n}
% 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} }
}
% \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:x}
% 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 { x }
% \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:x}
% 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 { x }
% \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}
%<@@=sys>
% \end{macrocode}
%
% \begin{macro}{\c__kernel_sys_dvipdfmx_version_int}
% A short excursion into the |sys| module to set up the backend version
% information.
% \begin{macrocode}
\group_begin:
\cs_set:Npn \@@_tmp:w #1 Version ~ #2 ~ #3 \q_stop {#2}
\sys_get_shell:nnNTF { extractbb~--version }
{ \char_set_catcode_space:n { `\ } }
\l_@@_internal_tl
{
\int_const:Nn \c__kernel_sys_dvipdfmx_version_int
{
\exp_after:wN \@@_tmp:w \l_@@_internal_tl
\q_stop
}
}
{ \int_const:Nn \c__kernel_sys_dvipdfmx_version_int { 0 } }
\group_end:
% \end{macrocode}
% \end{macro}
%
% \begin{macrocode}
%<@@=>
% \end{macrocode}
%
% \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:x}
% 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 { x }
% \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:x}
% \begin{macro}{\__kernel_backend_scope:n, \__kernel_backend_scope:x}
% 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 { x }
\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 { x }
% \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macrocode}
%</dvisvgm>
% \end{macrocode}
%
% \begin{macrocode}
%</package>
% \end{macrocode}
%
% \end{implementation}
%
% \PrintIndex