% Simple graphics overlay environment fo TikZ.
%
%  By Nathan Dunfield.   This code is in the public domain. 
%
% USAGE:  \begin{tikzoverlay}[<graphics opts>]{file name}[tikz opts]
%              (tikz commands in coordinate system where horizontal
%              direction is 100)
%              \end{tikzoverlay}
%
% The variant tikzoverlayabs uses coordinates going from (0,0) to (1,1).
%
% Modeled on 
%
% http://bazaar.launchpad.net/~tex-sx/tex-sx/development/view/head:/onimage.dtx

\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{tikzoverlay}[2012/07/18]
\RequirePackage{tikz}

\makeatletter

\def\tikzoverlay{%
    \pgfutil@ifnextchar[{\tikzoverlay@opt}{\tikzoveraly@opt[]}%
}
\def\tikzoverlay@opt[#1]#2{%
    \begin{tikzpicture}
        \node[anchor=south west, inner sep=0] (image) at (0,0) {\includegraphics[#1]{#2}};
        \newdimen\nmd@tikzoverlaywidth
        \pgfextractx{\nmd@tikzoverlaywidth}{\pgfpointanchor{image}{south east}}
        \begin{scope}
          \tikzset{x=0.01\nmd@tikzoverlaywidth}
          \tikzset{y=0.01\nmd@tikzoverlaywidth}
}
\def\endtikzoverlay{%
    \end{scope}
    \end{tikzpicture}
}

\def\tikzoverlayabs{%
    \pgfutil@ifnextchar[{\tikzoverlayabs@opt}{\tikzoveralyabs@opt[]}%
}
\def\tikzoverlayabs@opt[#1]#2{%
    \begin{tikzpicture}
        \node[anchor=south west, inner sep=0] (image) at (0,0) {\includegraphics[#1]{#2}};
        \begin{scope}
          \tikzset{x=(image.south east)}
          \tikzset{y=(image.north west)}
}
\def\endtikzoverlayabs{%
    \end{scope}
    \end{tikzpicture}
}

\makeatother