% Created by Stephen Haptonstahl
% May be used freely.  If something happens using this, it's not my fault.

\ProvidesPackage{hapgraph}[2003/11/17 Stephen Haptonstahl's graph paper macros]

\RequirePackage{calc}   % used to do arithmetic within LaTeX code.
\RequirePackage{ifthen}

\newboolean{pdftrue}
\setboolean{pdftrue}{false}
\DeclareOption{pdf}{\setboolean{pdftrue}{true}}
\ProcessOptions

\ifthenelse{\boolean{pdftrue}}
    {\RequirePackage[usenames,dvipsnames,pdftex]{color}}
    {\RequirePackage[usenames,dvipsnames]{color}}

% Various graph paper macros

% Create the ngrid environment
% ngrid is a grid from -n to n with axes in black and a grid in gray.
% Then the user can add commands within the picture environment to
% create a graph on the grid.
%
% The first parameter is the size of the grid in mm.  The second parameter
% is n, the number +/- from the origin.

    \newcounter{ngridleftborder}
    \newcounter{ngridrightborder}
    \newcounter{ngridspan}
    \newcounter{ngridlines}
    \newcounter{ngridtwon}

\newenvironment{ngrid}[2]{
    \setcounter{ngridleftborder}{-1-#2}
    \setcounter{ngridrightborder}{1+#2}
    \setcounter{ngridspan}{2*\value{ngridrightborder}}
    \setcounter{ngridlines}{\value{ngridspan}-1}
    \setcounter{ngridtwon}{2*#2}
    \setlength{\unitlength}{#1mm}\begin{picture}(\value{ngridspan},\value{ngridspan})(\value{ngridleftborder},\value{ngridleftborder})
        \textcolor{Gray}{
            \multiput(-#2,-#2)(1,0){\value{ngridlines}}{\line(0,1){\value{ngridtwon}}}
            \multiput(-#2,-#2)(0,1){\value{ngridlines}}{\line(1,0){\value{ngridtwon}}}
        }
        \linethickness{.75pt}
        \put(0,0){\vector(0,1){\value{ngridrightborder}}}
        \put(0,0){\vector(0,-1){\value{ngridrightborder}}}
        \put(0,0){\vector(1,0){\value{ngridrightborder}}}
        \put(0,0){\vector(-1,0){\value{ngridrightborder}}}
    }
    {\end{picture}}

% These commands \fivegrid and \tengrid create blank grids from -5 to 5 or 
% -10 to 10 using the ngrid environment.
\newcommand{\fivegrid}[1]{ \begin{ngrid}{#1}{5} \end{ngrid} }
\newcommand{\tengrid}[1]{ \begin{ngrid}{#1}{10} \end{ngrid} }