Piano/Xylophone key diagrams

[Phil Holmes]

At college, one of my ensembles is a mixed-music group performing modern 
music.  I normally get away with singing or "playing" a triangle and bits of 
other untuned percussion.  Imagine my surprised when I was given a xylophone 
piece to play.  Fortunately, it's only one note at a time, and most of them 
are the same note, repeated for four bars, so I generally have the time to 
work out where the next key is when I'm playing the current one.  However, I 
thought it might be interesting and vaguely useful to have some piano key 
diagrams which show which key is to be played, rather like the fingering 
diagrams.  The attached image illustrates the kind of thing: playing D#.

I know I could use box, rounded-box or filled-box, or moveto/lineto commands 
to draw the boxes, so I clearly could create the diagrams individually for 
each note.  However, I thought it would be better to create a function to do 
this.  I'd presume the location of each box would be in some sort of 
array/list, and that the function would use the 'pitch of the note to 
determine which to fill.  However, I've read our documentation on scheme and 
am stuck on how to start, either creating the array/list and iterating over 
it to draw boxes, or grabbing the pitch value of a note.

Could anyone start me off on this and help when I get stuck again?

TIA.

--
Phil Holmes

Keys.png
Description: PNG image