% \iffalse
%<*driver>
\def\nameofplainTeX{plain}
\ifx\fmtname\nameofplainTeX\else
    \expandafter\begingroup
\fi
\input docstrip %
\askforoverwritefalse
\preamble

MIT License

Copyright (c) 2021-2022 Magnus Lie Hetland

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

\endpreamble
% stop docstrip adding \endinput
\postamble
\endpostamble
\generate{\file{abspos.sty}{\from{abspos.dtx}{package}}}
\ifx\fmtname\nameofplainTeX
    \expandafter\endbatchfile
\else
    \expandafter\endgroup
\fi
%</driver>
%
%<*driver|package>
\RequirePackage{expl3}
%<driver|package>
%
%<*driver>
\documentclass[full]{l3doc}
\usepackage{graphicx}
\usepackage[export]{adjustbox}
\usepackage{tcolorbox}
\tcbuselibrary{listings,skins}
\usepackage{xcoffins}
\usepackage{abspos}

\lstdefinestyle{tcblatex}{language={[LaTeX]TeX},
    columns=fullflexible,
    keepspaces=true,
    breaklines=true,
    breakatwhitespace=true,
    basicstyle=\ttfamily\small\color{black!80},
    extendedchars=true,
    nolol,
    inputencoding=\kvtcb@listingencoding,
    literate={~}{\textcolor{gray}{\raisebox{-.75ex}{\textasciitilde}}}{1},
    commentstyle=\color{gray},
}

\DeclareTCBInputListing \Example { m } {
    listing only,
    listing file=demo#1,
    tile,
    finish={
        \draw (frame.north west) + (-\marginparsep,0pt)
            node[line width=0pt, inner sep=0pt, anchor=north east]
            {\includegraphics[page=#1, frame, width=\marginparwidth]{demo}}
        ;
    }
}

\ExplSyntaxOn
\cs_set:Npn \__codedoc_macro_end_style:n #1 {}
\ExplSyntaxOff

\begin{document}
    \DocInput{\jobname.dtx}
\end{document}
%</driver>
%
%<*package>
\ProvidesExplPackage {abspos} {2022-09-22} {0.1}
    {Absolute placement with coffins}
%</package>
% \fi
%
% \title{The \pkg{abspos} package\\ Absolute placement with coffins}
% \author{Magnus Lie Hetland}
%
% \maketitle
%
% \begin{documentation}
%
% \noindent
% The \pkg{abspos} package lets you place contents at an absolute position,
% anchored at some specified part of the content, similar to how \pkg{tikz}
% nodes work, though without using the two-pass strategy of \pkg{tikz}. It also
% avoids messing with the order of \pkg{beamer} overlays, which is what happens
% when one uses the \pkg{textpos} package with the \pkg{overlay}
% option.\footnote{Another possible solution is to use the \pkg{pst-abspos}
% package, which relies on \pkg{pstricks}.} The solution used is quite
% straightforward, combining \emph{coffins} (using \pkg{l3coffins}) with the
% placement mechanisms of \pkg{atbegshi}.
%
% The main command of the package is |\absput|, which is somewhat similar to the
% |\put| command of the \LaTeX\@ |picture| environment.
% By default, it places its contents in the middle of the page, so
% |\absput{Hello}| will put the word ``Hello'' front and center. Variations
% are then possible using an optional argument consisting of keys and key--value
% pairs, as shown in the following.
%
% \Example{1}
%
% \noindent
% Supplying a |width| creates a vertical box. If the surrounding text is set,
% for example, using \cs{raggedright} (as is common in \pkg{beamer}), the
% contents of the \cs{absput} command will be, too. So if you want your text
% justified, you can use something like the \cs{justifying} command from
% \pkg{ragged2e}.
%
% \Example{2}
%
% \noindent
% The options can also be set globally (or within a group) using
% \cs{absposset}. For example, if you with to scale everything you place by a
% certain amount, you could do that as in the following.
%
% \Example{3}
%
% \noindent
% By default, the contents are placed \emph{in front} of the current page, but
% this can be modified by supplying your own ``page coffin'' (an \pkg{l3coffins}
% or \pkg{xcoffins} coffin) and typesetting that with, e.g., \pkg{atbegshi}. If,
% for example, you wish to place something in the background of every slide of a
% \pkg{beamer} presentation, you could do that by adding the following to the
% preamble.\footnote{Note that because it will end up behind even the slide
% itself, you need to remove the background color, by setting |bg| to nothing,
% as in the example code. If you want it behind the content, but still have a
% background color, you would need to add that yourself, with a colored box or
% filled \pkg{tikz} rectangle, possibly also using the \cs{absput} command.}
%
% ^^A Can't use tcblisting, because it uses \lstinputlisting, which doesn't
% ^^A respect `gobble`
% \begin{tcolorbox}[tile]
% \begin{lstlisting}[gobble=2, style=tcblatex]
% \setbeamercolor{background canvas}{bg=} % So the coffin isn't obscured
%
% \NewCoffin \MyPageCoffin
% \AtBeginShipout{
%     \AtBeginShipoutUpperLeft{
%         \TypesetCoffin \MyPageCoffin [t,l] (0pt,0pt)
%     }
% }
% \end{lstlisting}
% \end{tcolorbox}
%
% \noindent
% Now simply add a \cs{absput} command at the beginning of the document, before
% your first |frame| (after |\begin{document}|), using |pg=\MyPageCoffin| to
% specify which coffin to use for rendering and positioning contents. This gives
% you a coordinate system starting at the top left corner of the page. If you
% wish to anchor your positioned elements elsewhere, you'll need to resize your
% page coffin (see p.~\pageref{p:reset}).
%
% \section*{Reference}
%
% \begin{function}{\absposset}
% \begin{syntax}
%   \cs{absposset} \marg{options}
% \end{syntax}
% Sets the options, as described under \cs{absput}, to the value they should
% have within the current group (or globally, if not inside a group).
% \end{function}
%
% \begin{function}{\absput}
% \begin{syntax}
%   \cs{absput} \oarg{options} \marg{contents}
% \end{syntax}
% Places \meta{contents} at some position (possibly scaled or rotated) as
% dictated by the optional \meta{options}, supplied as keys and key--value
% pairs. The \emph{defaults} are used as values if only the keys are given, and
% the \emph{initial values} are used if the options are not specified. The
% available options are as follows.
% \end{function}
% \begin{itemize}
%
%     \item |angle=|\meta{angle}: The angle to which the coffin is rotated
%     before being positioned.
%
%     No default. Initial value |0|.
%
%     \item |h=|\meta{h-anchor}: The horizontal anchor to use for positioning.
%     This corresponds to a \pkg{l3coffins} (or \pkg{xcoffins}) \emph{pole}. The
%     available anchors are |l| for left, |hc| for center and |r| for right.
%     These are also available as separate valueless keys, so if you supply
%     \cs{absput} with the key |l|, that is equivalent to using |h=l|, etc.
%
%     There are also two-letter shortcuts defined for setting the horizontal and
%     vertical anchors simultaneously, with the vertical one first. For example,
%     |tl| is equivalent to |v=t,h=l|. In these double shortcuts, the prefixes
%     |h| and |v| have been stripped from the center anchors, so that bottom
%     center is |bc|, for example, and not |bhc|.
%
%     No default. Initial value |hc|, which centers the coffin horizontally at
%     \meta{x-coord}.
%
%     \item |pg=|\meta{page-coffin}: Supplies the coffin to use as the
%     page, or ``canvas,'' for placing the contents.
%
%     No default. The initial value is an internal canvas that is rendered in
%     front of the current page (on shipout), and then cleared.
%
%     \item |pg-h|=\meta{page-h-anchor}: Similar to |h|, except that it applies
%     to the canvas (set by |pg|). Shortcuts (like |pg-l| for |pg-h=l|) are
%     defined for the default anchors (|l|, |hc|, |r|).
%
%     Double shortcuts are defined for |pg-h| and |pg-v| in a similar manner to
%     those defined for |h| and |v|, so that |pg-tl| is equivalent to
%     |pg-v=t,pg-h=l|.
%
%     No default. Initial value |hc|.
%
%     \item |pg-v|=\meta{page-v-anchor}: Similar to |v|, except that it applies
%     to the canvas (set by |pg|). Shortcuts (like |pg-t| for |pg-v=t|) are
%     defined for the default anchors (|t|, |vc|, |b|, |T|, |B|, |H|).
%
%     Combined shortcuts such as |pg-tl| and |pg-br|, etc., are also defined.
%     See the descriptions of |h| and |pg-h| for more.
%
%     No default. Initial value |vc|.
%
%     \item |scale=|\meta{scale}: The factor by which the coffin is scaled.
%
%     No default. If |scale| is not used, no scaling is performed.
%
%     \item |v=|\meta{v-anchor}: The vertical anchor to use for positioning (see
%     |h|). The available anchors are |t| for top, |vc| for center, |b| for
%     bottom and |H| for baseline. These are also available as separate
%     valueless keys, so if you supply \cs{absput} with the key |t|, that is
%     equivalent to using |v=t|, etc.
%
%     Note that if the |width| key is set, a vertial coffin is used, which makes
%     the additional anchors (or poles) |T| (baseline of the first line, or
%     other material at the top) and |B| (baseline for the last line, or other
%     material at the bottom).
%
%     Combined shortcuts such as |tl| and |br|, etc., are also defined. See the
%     description of |h| for more.
%
%     No default. Initial value |vc|, which centers the coffin vertically at
%     \meta{y-coord}.
%
%     \item |width=|\meta{width}: Set the width constraining the contents,
%     before scaling. If this is set, the contents are set in vertical mode;
%     otherwise, they are set in horizontal mode.
%
%     No default and no initial value.
%
%     \item |x=|\meta{x-coord}: The $x$ coordinate, measured from the current
%     horizontal page anchor, set by |pg-h|.
%
%     No default. Initial value |0pt|.
%
%     \item |y=|\meta{y-coord}: The $y$ coordinate, measured from the current
%     vertical page anchor, set by |pg-v|.
%
%     No default. Initial value |0pt|.
% \end{itemize}
%
% \begin{function}{\absputcoffin}
% \begin{syntax}
%   \cs{absputcoffin} \oarg{options} \meta{coffin}
% \end{syntax}
% Places \meta{coffin} at some position (possibly scaled or rotated), just like
% \cs{absput}. The difference is that a coffin is provided directly, rather than
% constructed by typesetting some supplied contents. This means that the |width|
% key is not used, though it is permitted for consistency (and ease of reusing
% option lists).
% \end{function}
%
% \end{documentation}
%
% \begin{implementation}
%
% \section*{Implementation}
%
%    \begin{macrocode}
%<*package>
%<@@=apos>
%    \end{macrocode}
%
% \noindent
% First, we need to import the necessary packages. We're using \pkg{expl3} to
% set up the package, so we get \pkg{l3coffins} for free (and cannot import it
% directly, anyway). If \pkg{abspos} is used with \pkg{beamer}, then
% \pkg{atbegshi} is already included. Elsewhere, though, it will not be, so we
% require it here.
%
%    \begin{macrocode}
\RequirePackage{atbegshi}
%    \end{macrocode}
%
% \noindent
% We make sure we have the variants we need of some existing commands:
%
%    \begin{macrocode}
\cs_generate_variant:Nn \tl_if_novalue:nTF       { VTF }
\cs_generate_variant:Nn \tl_if_novalue:nF        { VF }
\cs_generate_variant:Nn \coffin_gattach:NnnNnnnn { NooNoonn }
%    \end{macrocode}
%
% \begin{variable}{\g_apos_shipout_coffin}
%
% This variable is normally used to store the contents to be placed on the
% current page. It accumulates the contents from every call to \cs{absput} until
% the page is about to be typeset (shipped out), at which point
% \cs{g_apos_shipout_coffin} is typeset in front.
%
%    \begin{macrocode}
\coffin_new:N \g_apos_shipout_coffin
%    \end{macrocode}
% \end{variable}
%
% \begin{macro}{\apos_reset_shipout_coffin:}\label{p:reset}
% Used to initialize, and later reinitialize, the shipout coffin, to simply be
% an empty coffin with the width and height of the current page.
%    \begin{macrocode}
\cs_new:Npn \apos_reset_shipout_coffin: {
    \hcoffin_gset:Nn \g_apos_shipout_coffin {
        \phantom{\rule{\paperwidth}{\paperheight}}
    }
}
%    \end{macrocode}
% \end{macro}
%
% \noindent
% The following hook ensures that that \cs{g_apos_shipout_coffin} is typeset in
% front of the page as it is being shipped out (anchored top left), and then
% cleared, ready to accumulate contents for the next page. The \pkg{atbegshi}
% command used wraps its contents in a |picture| environment, which we don't
% really need, but it seems to be more trouble than it's worth to get rid of it.
%
%    \begin{macrocode}
\apos_reset_shipout_coffin:
\AtBeginShipout{
    \AtBeginShipoutUpperLeftForeground{
        \coffin_typeset:Nnnnn \g_apos_shipout_coffin {t} {l} {0pt} {0pt}
        \apos_reset_shipout_coffin:
    }
}
%    \end{macrocode}
%
% \begin{variable}{\g_apos_canvas_coffin}
%
% This variable is used as part of the |pg| key, and is initially set equal to
% \cs{g_apos_shipout_coffin}, so that whatever is rendered to the canvas (i.e.,
% \cs{g_apos_canvas_coffin}) is placed on top of the page contents on shipout,
% and then cleared. If a different behavior is desired, another coffin can can
% be supplied instead. Rather than constructing a coffin, we just set up a token
% list, which initially will be aliased to the actual coffin
% \cs{g_apos_shipout_coffin} as part of the key handling.
%    \begin{macrocode}
\tl_new:N \g_apos_canvas_coffin
%    \end{macrocode}
% \end{variable}
% \begin{macro}{\apos_reset_overlay:}
% This is a utility to reset \pkg{beamer} overlay specifications at the end of
% our coffin contents. The idea is that if we use, say, \cs{pause} inside
% \cs{absput}, then everything after the \cs{pause} command will be paused,
% including material \emph{outside} \cs{absput}. To restrict such commands to the
% contents provided to \cs{absput}, we use \cs{onslide<1->} after typesetting the
% contents in our coffin. This is only useful (or possible) when using
% \pkg{beamer}, so otherwise, we just alias \cs{ap_reset_overlay:} to
% \cs{relax}, i.e., don't do anything.
%    \begin{macrocode}
\tl_new:N \apos_reset_overlay:
\@ifclassloaded{beamer}
    { \tl_gset:Nn    \apos_reset_overlay: { \onslide<1-> } }
    { \tl_gset_eq:NN \apos_reset_overlay:   \relax         }
%    \end{macrocode}
% \end{macro}
%
% \noindent
% We now define the various keys used to configure \cs{absput}, as described
% in the reference.
%
%    \begin{macrocode}
\keys_define:nn { abspos } {

    angle .tl_set:N          = \l_apos_angle_tl,
    angle .initial:V         = \c_novalue_tl,
    angle .value_required:n  = true,

    h     .tl_set:N          = \l_apos_hanchor_tl,
    h     .initial:n         = hc,
    h     .value_required:n  = true,

    pg    .code:n            = { \tl_set_eq:NN \g_apos_canvas_coffin #1 },
    pg    .initial:n         = \g_apos_shipout_coffin,
    pg    .value_required:n  = true,

    pg-h  .tl_set:N          = \l_apos_on_hanchor_tl,
    pg-h  .initial:n         = hc,
    pg-h  .value_required:n  = true,

    pg-v  .tl_set:N          = \l_apos_on_vanchor_tl,
    pg-v  .initial:n         = vc,
    pg-v  .value_required:n  = true,

    scale .tl_set:N          = \l_apos_scale_tl,
    scale .initial:V         = \c_novalue_tl,
    scale .value_required:n  = true,

    v     .tl_set:N          = \l_apos_vanchor_tl,
    v     .initial:n         = vc,
    v     .value_required:n  = true,

    width .tl_set:N          = \l_apos_width_tl,
    width .initial:V         = \c_novalue_tl,
    width .value_required:n  = true,

    x     .tl_set:N          = \l_apos_x_tl,
    x     .initial:n         = { 0pt },
    x     .value_required:n  = true,

    y     .tl_set:N          = \l_apos_y_tl,
    y     .initial:n         = { 0pt },
    y     .value_required:n  = true,

}

\clist_const:Nn \@@_hanchors_clist {l,hc,r}
\clist_const:Nn \@@_vanchors_clist {t,vc,b,H,T,B}

\cs_new:Npn \@@_define_shortcuts:nnn #1 #2 #3 {
    \keys_define:nn { abspos } {

    #1    .meta:n            = { #2 },
    #1    .value_forbidden:n = true,

    pg-#1 .meta:n            = { #3 },
    pg-#1 .value_forbidden:n = true,

    }
}

\cs_generate_variant:Nn \@@_define_shortcuts:nnn { Vnn }

\clist_map_inline:Nn \@@_hanchors_clist {

    \@@_define_shortcuts:nnn { #1 } { h = #1 } { pg-h = #1 }

}

\clist_map_inline:Nn \@@_vanchors_clist {

    \@@_define_shortcuts:nnn { #1 } { v = #1 } { pg-v = #1 }

}

\clist_map_inline:Nn \@@_vanchors_clist {
    \clist_map_inline:Nn \@@_hanchors_clist {

        \tl_clear:N \g_tmpa_tl

        \tl_if_eq:nnTF { #1 } { vc }
            { \tl_put_right:Nn \g_tmpa_tl { c } }
            { \tl_put_right:Nn \g_tmpa_tl { #1 } }

        \tl_if_eq:nnTF { ##1 } { hc }
            { \tl_put_right:Nn \g_tmpa_tl { c } }
            { \tl_put_right:Nn \g_tmpa_tl { ##1 } }

        \@@_define_shortcuts:Vnn
            \g_tmpa_tl { v = #1, h = ##1 } { pg-v = #1, pg-h = ##1 }

    }
}
%    \end{macrocode}
% In order to let the user set options outside the actual use of \cs{absput} and
% \cs{absputcoffin}, we introduce a wrapper:
%    \begin{macrocode}
\NewDocumentCommand \absposset { +m } {
    \keys_set:nn { abspos } { #1 }
}
%    \end{macrocode}
%
% \begin{macro}{\absput}
% This is the main command of the package. It takes a key--value list as its
% first optional argument, followed by the contents that are to be placed.
%    \begin{macrocode}
\NewDocumentCommand \absput { +O{ } +m } {
    \group_begin:
%    \end{macrocode}
% First we handle the keys, updating variables holding coordinates, etc.
%    \begin{macrocode}
    \keys_set:nn { abspos } { #1 }
%    \end{macrocode}
% Then the contents are typeset, with some additions, into a temporary coffin.
% The additions are that whitespace is stripped around the contents, and that we
% reset any overlay counters (in case they are modified by \cs{onslide} or
% \cs{pause}, or the like). If we're not using \pkg{beamer}, this last part is a
% no-op.
%
% If |width| has been set, the contents is set in vertical mode (using the given
% width); otherwise, it is set in horizontal mode.
%    \begin{macrocode}
    \tl_set:Nn \l_tmpa_tl {
        \ignorespaces #2 \unskip
        \apos_reset_overlay:
    }
    \tl_if_novalue:VTF \l_apos_width_tl {
        \hcoffin_set:Nn \l_tmpa_coffin \l_tmpa_tl
    } {
        \vcoffin_set:Nnn \l_tmpa_coffin \l_apos_width_tl \l_tmpa_tl
    }
%    \end{macrocode}
% Finally, actually place the typeset coffin on the canvas coffin.
%    \begin{macrocode}
    \@@_absput_coffin:N \l_tmpa_coffin
    \group_end:
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\absputcoffin}
%    A thin wrapper around the internal \cs{@@_absput_coffin:N}. The only extra
%    work done here is setting the keys.
%    \begin{macrocode}
\NewDocumentCommand \absputcoffin { +O{ } m } {
    \group_begin:
    \keys_set:nn { abspos } { #1 }
    \@@_absput_coffin:N #2
    \group_end:
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\@@_absput_coffin:N}
% An internal macro for placing a given coffin, using the options currently in
% effect (i.e., as configured by \cs{keys_set:nn} in some outer group). Used by
% \cs{absput} and \cs{absputcoffin}.
%    \begin{macrocode}
\cs_new:Npn \@@_absput_coffin:N #1 {
%    \end{macrocode}
% If a scale has been provided, we scale the temporary coffin (with the same
% factor in both directions).
%    \begin{macrocode}
    \tl_if_novalue:VF \l_apos_scale_tl {
        \coffin_scale:Nnn #1 \l_apos_scale_tl \l_apos_scale_tl
    }
%    \end{macrocode}
% If an angle has been provided, we rotate the temporary coffin.
%    \begin{macrocode}
    \tl_if_novalue:VF \l_apos_angle_tl {
        \coffin_rotate:Nn #1 \l_apos_angle_tl
    }
%    \end{macrocode}
% We now join the temporary coffin to our canvas coffin, so it will be rendered
% at the correct position at shipout.
%    \begin{macrocode}
    \coffin_gattach:NooNoonn
        \g_apos_canvas_coffin
            {\l_apos_on_hanchor_tl} {\l_apos_on_vanchor_tl}
        #1
            {\l_apos_hanchor_tl} {\l_apos_vanchor_tl}
            {\l_apos_x_tl} {\l_apos_y_tl}
%    \end{macrocode}
%
% \noindent
% Ideally, what we just did should have been enough. However, until
% October~2021, the \cs{coffin_gattach:} command was not actually
% global,\footnote{\url{https://tex.stackexchange.com/questions/618198}} so
% to have our modification take effect outside the current group also for older
% versions of \pkg{l3coffins}, we perform a final (normally redundant) global
% self-assignment before ending the \cs{absput} command.
%
%    \begin{macrocode}
    \coffin_gset_eq:NN \g_apos_canvas_coffin \g_apos_canvas_coffin
}
%    \end{macrocode}
% \end{macro}
%    \begin{macrocode}
%</package>
%    \end{macrocode}
%
% \end{implementation}