how to show symbols on top of LilyPond scores?

Santa offered a toy keyboard to my 4-year-old. He enjoys the provided scores, but I'd like to add some songs that we sing together and that are not included in the basic set. Every Key has a symbol (circle, triangle, square) and a color (blue, yellow, purple, red, orange) that is displayed on top of the music score, to help him figure out which keys to press.

I'm not a musician, but I do have a basic understanding on how to write music scores. I've never used lilypond, but I'm a developer and I know latex.

I tried searching for a way to add extra symbols, but I'm not sure this is feasible.

Solution

You can draw theses symbols by using some of the various graphics commands found on this page:
https://lilypond.org/doc/v2.24/Documentation/notation/graphic

Store these as markup macros at the top of the LilyPond file, and then call them in the score at the appropriate places.

\version "2.24.0"

blueTriangle = \markup {
    \left-align
    \with-color "blue"
    \triangle ##t
}

orangeCircle = \markup {
    \left-align
    \with-color "orange"
    \draw-circle #1 #0 ##t
}

purpleCircle = \markup {
    \left-align
    \with-color "purple"
    \draw-circle #1 #0 ##t
}

greenSquare = \markup {
    \left-align
    \with-color "green"
    \filled-box #'(0 . 2) #'(0 . 2) #0
}

\new Staff {
    g4^\blueTriangle
    d'^\orangeCircle
    b'^\purpleCircle
    f''^\greenSquare
}

This will be a bit tedious if you are placing a symbol above every note. But if you know Scheme you can probably devise a function that reads the note letters and octaves and places the correct symbol in automatically.