I developed an intuitive interface for music notation.
I created this to facilitate picking notes for the fingering chart apps, and have utilized it in most every app since.
The instinctive gesture of touching the staff seemed so natural, and then to slide right for sharp and left for flat was simply the next step.
To make it easier to choose sharps or flats, I decided that touching along the right or left side would be a natural progression to automatically set a sharp or flat note.
The formulas for manipulating the images of notes and accidentals has developed over time, becoming more versatile and streamlined with each implementation.
Twelve Tone introduced the ability to notate more than one note on the same staff. Up to twelve actually. So I had to isolate the controls for each note to its own area. This opened up more opportunities and I eventually incorporated it, and rhythmic values, into Woodshed to allow the creation of custom exercises. Implementing more complexity with rests, barlines, and pickup notes created Melody Composer. Note values and triplet figures automatically tie and extend over barlines. Notation should serve the music you want, not dictate it. There are limitations to Melody Composer, but it's a handy tool for composers.
The piano keyboard is familiar to us all whether the piano is our primary instrument or not.
We have all been taught where middle C is - or at least how to find a C somewhere on the piano and we can guess which one is the most middle. So, the keyboard interface was started with a pretty obvious understanding.