%!

<< /PageSize [842 595] >> setpagedevice

gsave

% Find out if the device space is rotated compared to user space.
% This turns out to be important!
% We assume if we have a non-zero in index one, then we're rotated by 90 degrees
6 array currentmatrix 1 get 0 ne dup
    { 160 } { 120 } ifelse /YDivisions exch def
    { 120 } { 160 } ifelse /XDivisions exch def


0 0 itransform % Device origin
480 add exch 640 add exch % rough grid size 
transform % to device space

round cvi YDivisions idiv 
    dup /DeviceHPitch exch def 
    YDivisions mul /DeviceGridHeight exch def
round cvi XDivisions idiv 
    dup /DeviceVPitch exch def 
    XDivisions mul /DeviceGridWidth exch def

DeviceGridWidth DeviceGridHeight itransform 0 0 itransform
exch 3 1 roll
sub /UserGridHeight exch def
sub /UserGridWidth exch def

842 UserGridWidth sub 2 div
595 UserGridHeight sub 2 div
2 copy
/UserGridBottomLeftY exch def
/UserGridBottomLeftX exch def
transform
round cvi /DeviceGridBottomLeftY exch def
round cvi /DeviceGridBottomLeftX exch def


[ 1 0 0 1 DeviceGridBottomLeftX DeviceGridBottomLeftY ] setmatrix

0 setlinewidth

% Should return something like [[2Pitch/5 Pitch/5 Pitch/5 Pitch/5] Pitch/5]
% Element 0 (Representing the corners) is made to be bigger, and the other values are made to fit
% I think this will do something broadly sensible for grid pitches > 2 device units
% The intent is something like +  -  +   -  + with the corners intersecting the lines coming the other way
% but it will fall back to +  + if there's no space for a middle stroke, and will just dash lines otherwise.
/MakeDashPattern {
    [ exch abs dup % ([ pitch pitch)
    [ exch % Bring line pitch (gap to fill) to top of stack. We'll keep it at the top as we go
        dup 5 div ceiling cvi 2 mul % corners - if pitch is =< 2, this will be weird
        dup neg % ( [ pitch [ pitch corners -corners )
        3 2 roll add  % Bring gap to fill to the top, and update ( [ pitch [ corners gap)
        % Gap may be =<0 
        dup 0 gt { % if 
            % Leave a copy of the gap, in case we aren't able to split it
            dup  % ( ... corners biggap biggap)
            % If gap is bigish we'll definitely want a centre stroke even if it's an even number
            % so we reserve up to a third of the gap before dividing by two to get space width.
            dup dup 3 div floor cvi sub 2 idiv  % (... corners biggap biggap space)
            dup 0 le { % if
                % If we can't split the gap, use the whole gap as space
                pop pop
            } { % else
                % Make a second copy of the space
                dup % ( ... corners biggap biggap space space)
                % Bring the gap to the top, and update, the new value is the centre stroke width
                dup -2 mul 4 3 roll add % (... corners biggap space space centre)
                dup 0 eq { % if
                    % Failed to split
                    pop pop pop % (... corners biggap)
                } { % else
                    % Manipulate stack so that the extra gap goes away, and centre is in the right place
                    exch 4 3 roll  % (... corners space centre space biggap)
                    pop % (... corners space centre space)
                } ifelse
            } ifelse
        } { % else
            pop
        } ifelse
    ] %( [ pitch [spacing] )
     exch 5 div ceiling cvi ]
} def

/HMinorTickDash DeviceVPitch MakeDashPattern def
/VMinorTickDash DeviceHPitch MakeDashPattern def


% Draw horizontal ticks
1 1 YDivisions 1 sub { % for
    dup 8 mod 0 eq { [] 0 } { HMinorTickDash 0 get HMinorTickDash 1 get } ifelse setdash
    DeviceHPitch mul 0 exch moveto
    DeviceGridWidth 0 rlineto stroke
} for

% Draw vertical ticks
1 1 XDivisions 1 sub { % for
    dup 8 mod 0 eq { [] 0 } { VMinorTickDash 0 get VMinorTickDash 1 get } ifelse setdash
    DeviceVPitch mul 0 moveto
    0 DeviceGridHeight rlineto stroke
} for

grestore

1 setlinewidth 0 setgray
1 setlinejoin

UserGridBottomLeftX UserGridBottomLeftY translate
0.5 0.5 moveto
0 UserGridHeight 1 add rlineto
UserGridWidth 1 add 0 rlineto
0 -1 UserGridHeight sub rlineto
closepath stroke

/UserPixelHeight UserGridHeight 120 div def
/UserPixelWidth UserGridWidth 160 div def

/Courier findfont
6 scalefont
setfont

0 8 112 {
    dup -24 exch % x
    UserGridHeight exch 1 add UserPixelHeight mul sub
    moveto

    8 add ($00xx) dup 3 2 roll
    16 2 string cvrs
    dup length 3 exch sub exch putinterval
    show
} for

-10
0 8 152 {
    2 copy UserPixelWidth mul exch moveto

    ($xx00) dup 3 2 roll
    16 2 string cvrs
    dup length 5 exch sub exch putinterval
    show
} for
pop

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