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%% File: l3draw-layers.dtx
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% Copyright (C) 2019-2025 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
%
%    http://www.latex-project.org/lppl.txt
%
% This file is part of the "l3experimental 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>
\RequirePackage{expl3}
\documentclass[full]{l3doc}
\begin{document}
  \DocInput{\jobname.dtx}
\end{document}
%</driver>
% \fi
%
% \title{^^A
%   The \pkg{l3draw-layers} package\\ Layers^^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 2025-10-09}
%
% \maketitle
%
% \begin{implementation}
%
% \section{\pkg{l3draw-layers} implementation}
%
%    \begin{macrocode}
%<*package>
%    \end{macrocode}
%
%    \begin{macrocode}
%<@@=draw>
%    \end{macrocode}
%
% \subsection{User interface}
%
% \begin{macro}{\draw_layer_new:n}
%    \begin{macrocode}
\cs_new_protected:Npn \draw_layer_new:n #1
  {
    \str_if_eq:nnTF {#1} { main }
      { \msg_error:nnn { draw } { main-reserved } }
      {
        \box_new:c { g_@@_layer_ #1 _box }
        \box_new:c { l_@@_layer_ #1 _box }
      }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{variable}{\l_@@_layer_tl}
%   The name of the current layer: we start off with |main|.
%    \begin{macrocode}
\tl_new:N \l_@@_layer_tl
\tl_set:Nn \l_@@_layer_tl { main }
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_@@_layer_close_bool}
%   Used to track if a layer needs to be closed.
%    \begin{macrocode}
\bool_new:N \l_@@_layer_close_bool
%    \end{macrocode}
% \end{variable}
%
% \begin{variable}{\l_draw_layers_clist, \g_@@_layers_clist}
%   The list of layers to use starts off with just the |main| one.
%    \begin{macrocode}
\clist_new:N \l_draw_layers_clist
\clist_set:Nn \l_draw_layers_clist { main }
\clist_new:N \g_@@_layers_clist
%    \end{macrocode}
% \end{variable}
%
% \begin{macro}{\draw_layer_begin:n}
% \begin{macro}{\draw_layer_end:}
%   Layers may be called multiple times and have to work when nested. That
%   drives a bit of grouping to get everything in order. Layers have to be zero
%   width, so they get set as we go along.
%    \begin{macrocode}
\cs_new_protected:Npn \draw_layer_begin:n #1
  {
    \group_begin:
      \box_if_exist:cTF { g_@@_layer_ #1 _box }
        {
          \str_if_eq:VnTF \l_@@_layer_tl {#1}
            { \bool_set_false:N \l_@@_layer_close_bool }
            {
              \bool_set_true:N \l_@@_layer_close_bool
              \tl_set:Nn \l_@@_layer_tl {#1}
              \box_gset_wd:cn { g_@@_layer_ #1 _box } { 0pt }
              \hbox_gset:cw { g_@@_layer_ #1 _box }
                \box_use_drop:c { g_@@_layer_ #1 _box }
                \group_begin:
            }
          \draw_set_linewidth:n { \l_draw_default_linewidth_dim }
        }
        {
          \str_if_eq:nnTF {#1} { main }
            { \msg_error:nnn { draw } { unknown-layer } {#1} }
            { \msg_error:nnn { draw } { main-layer } }
        }
  }
\cs_new_protected:Npn \draw_layer_end:
  {
      \bool_if:NT \l_@@_layer_close_bool
        {
            \group_end:
          \hbox_gset_end:
        }
    \group_end:
  }
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \subsection{Internal cross-links}
%
% \begin{macro}{\@@_layers_insert:}
%   The |main| layer is special, otherwise just dump the layer box inside
%   a scope.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_layers_insert:
  {
    \clist_map_inline:Nn \l_draw_layers_clist
      {
        \str_if_eq:nnTF {##1} { main }
          {
            \box_set_wd:Nn \l_@@_layer_main_box { 0pt }
            \box_use_drop:N \l_@@_layer_main_box
          }
          {
            \@@_backend_scope_begin:
            \box_gset_wd:cn { g_@@_layer_ ##1 _box } { 0pt }
            \box_use_drop:c { g_@@_layer_ ##1 _box }
            \@@_backend_scope_end:
          }
      }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_layers_save:, \@@_layers_restore:}
%   Simple save/restore functions.
%    \begin{macrocode}
\cs_new_protected:Npn \@@_layers_save:
  {
    \clist_map_inline:Nn \l_draw_layers_clist
      {
        \str_if_eq:nnF {##1} { main }
          {
            \box_set_eq:cc { l_@@_layer_ ##1 _box }
              { g_@@_layer_ ##1 _box }
          }
      }
  }
\cs_new_protected:Npn \@@_layers_restore:
  {
    \clist_map_inline:Nn \l_draw_layers_clist
      {
        \str_if_eq:nnF {##1} { main }
          {
            \box_gset_eq:cc { g_@@_layer_ ##1 _box }
              { l_@@_layer_ ##1 _box }
          }
      }
  }
%    \end{macrocode}
% \end{macro}
%
% \begin{macrocode}
\msg_new:nnnn { draw } { main-layer }
  { Material~cannot~be~added~to~'main'~layer. }
  { The~main~layer~may~only~be~accessed~at~the~top~level. }
\msg_new:nnn { draw } { main-reserved }
  { The~'main'~layer~is~reserved. }
\msg_new:nnnn { draw } { unknown-layer }
  { Layer~'#1'~has~not~been~created. }
  { You~have~tried~to~use~layer~'#1',~but~it~was~never~set~up. }
% \end{macrocode}
%
%    \begin{macrocode}
%</package>
%    \end{macrocode}
%
% \end{implementation}
%
% \PrintIndex
