% at.sty     Colin Hogben (chah@jet.uk)
% 12-Aug-91  First version
% 20-Mar-92  Fixed to allow for \headheight
% 06-Jul-93  \@useat only used in case of any \at material (B.Gaulle)
%
% \at(HPOS,VPOS){TEXT}
% Positions TEXT at an absolute distance of HPOS from the left edge
% and VPOS from the top edge of the current page.
%
% Example:
%   \at(2cm,5cm){\parbox[t]{10cm}{
%       Name\\          % Recipient's name and address positioned
%       Address\\etc.}} % suitably for a windowed envelope
% -----------------------------------------------------------------
%
% First create a box in which to store absolute positioned material.
%
\newbox\@atbox
\newif\ifat\atfalse% --bg
%
% at(HPOS,VPOS){TEXT}
% Add the TEXT to the box with suitable offsets applied.
%
\long\def\at(#1,#2)#3{\setbox\@atbox=\hbox
 {\unhbox\@atbox
  \vtop to 0pt{\kern #2\hbox to 0pt{\kern #1\relax #3\hss}\vss}}%
 \attrue}% --bg
%
% Unload the saved absolute-positioned material.
% Teleport to the actual top corner of the page by undoing the header
% separation, the top and side margins, and the mysterious 1 inch
% offset applied to each. Then make it look like a singularity (zero
% height, depth and width).
%
\def\@useat{\ifat% --bg
  \vtop to 0pt{\kern-\headsep \kern-\topmargin \kern-\headheight \kern-1in
    \hbox to 0pt{\kern-\@themargin \kern-1in \unhbox\@atbox \hss}\vss}%
            \fi\atfalse}% --bg
%
% The following is a copy of the latex.tex \output routine except for
% line 1: this prepends the shifted absolute material to the current
% page. A little unsafe to copy code like this, but I couldn't work
% out where else to insert the box.
%
\output{\setbox255=\vbox{\@useat \unvbox255}%
  \ifnum\outputpenalty <-\@M\@specialoutput\else%
  \@makecol\@opcol\@floatplacement\@startcolumn%
  \@whilesw\if@fcolmade \fi{\@opcol\@startcolumn}\fi%
  \global\vsize\ifnum\outputpenalty >-\@Miv \@colroom%
                  \else \maxdimen\fi}%
%
\endinput% --bg