Re: Building a guitar chord using MP

[Vyatcheslav Yatskovsky <yatskovsky@gmail.com>]

Hurray!

I've got first draft version of guitar chord building macro. (With the 
help of this excellent manual http://www.tug.org/docs/metapost/mpman.pdf )

% -- working version ---
\startuseMPgraphic{chordgrid}{e,B,G,D,A,E}
def fretmark(expr a,b) =
	% a = string number
	% b = fret number
	pickup pencircle scaled 3pt;
	drawdot(b*7-3, a*4.5-4.5);
enddef;

drawoptions(withpen pencircle scaled 0.4pt withcolor black) ;
draw hlingrid(0, 5, 1, 0.8cm, 1cm) ;
draw vlingrid(0, 4, 1, 1cm, 0.8cm) ;

fretmark(1,\MPvar{e});
fretmark(2,\MPvar{B});
fretmark(3,\MPvar{G});
fretmark(4,\MPvar{D});
fretmark(5,\MPvar{A});
fretmark(6,\MPvar{E});
\stopuseMPgraphic

\define[6]\Ch
{\dontleavehmode
\useMPgraphic{chordgrid}{e={#1},B={#2},G={#3},D={#4},A={#5},E={#6}}%
\hskip2mm}

\starttext
\Ch{1}{3}{1}{2}{1}{4}
\stoptext


However, my current trouble is chord caption (like Am). Except wrong 
placement of the label, adding seventh non-numerical argument to the 
macro throws an error.

% -- does not work ---
\startuseMPgraphic{chordgrid}{e,B,G,D,A,E,Cptn}
def fretmark(expr a,b) =
	% a = string number
	% b = fret number
	pickup pencircle scaled 3pt;
	drawdot(b*7-3, a*4.5-4.5);
enddef;

drawoptions(withpen pencircle scaled 0.4pt withcolor black) ;
draw hlingrid(0, 5, 1, 0.8cm, 1cm) ;
draw vlingrid(0, 4, 1, 1cm, 0.8cm) ;

fretmark(1,\MPvar{e});
fretmark(2,\MPvar{B});
fretmark(3,\MPvar{G});
fretmark(4,\MPvar{D});
fretmark(5,\MPvar{A});
fretmark(6,\MPvar{E});

label.top(\MPvar{Cptn}, (2,0));
\stopuseMPgraphic

\define[7]\Ch
{\dontleavehmode
\useMPgraphic{chordgrid}{e={#1},B={#2},G={#3},D={#4},A={#5},E={#6},Cptn={#7}}%
\hskip2mm}

\starttext
\Ch{1}{3}{1}{2}{1}{4}{Am}
\stoptext


! Missing number, treated as zero.
<to be read again>
                    A
\theMPvariable ->A
                   m
<argument> ...\hbox {\scratchdimen \theMPvariable
                                                   sp}\ifdim \wd 
\scratchbox ...
\secondoftwoarguments #1#2->#2

\prepareMPvariable ...epareMPvariable {\@@meta #1}
                                                   \fi
\next1 #1,->\prepareMPvariable {#1}
                                    \doprocesscommaitem
...
l.29 \Ch{1}{3}{1}{2}{1}{4}{Am}

?


Regards,
Vyatcheslav
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