Fretless MIDI guitar neck

Hello! I’ve been using this forum a lot when doing research but this is my first time actually posting.
I’m trying to build a USB MIDI controller that can be played like a guitar but I can’t figure out how to design the neck.

My requirements are:

  • It has to be USB (I want it to be as flexible as possible without an audio interface)
  • Dimensions should be roughly 4 x 40 cm (precise width is not as critical)
  • It has to be multi touch (it would be best if I didn’t have to wear any “glove”)
  • It should be “invisible” from the outside (no sensor matrix visible)
  • The “pixel” size should be no more than 5 mm2
    About the last point, I want this to be fret-less and string-less so I can change how many strings and frets it has (if any) in software depending on what virtual instrument I’m controlling.

Basically I need a long and thin touch panel.

I’ve done some research and I decided that capacitive sensing could be the best method since it can be hidden behind a smooth panel and disappear, so my first idea was to make a grid of small nails/rivets/studs however I feel like the number of points required would be way to much for an Arduino at the refresh rate required to play.

I came across tft overlays (such as) but what I found didn’t have multi touch capabilities and IR based touch screen solutions which I think wouldn’t work well in variable light conditions.

Then I thought of using actual display modules since it would be cool to have visual feedback or animations under my fingers but I couldn’t find anything where the screen ended flush so to stack them next to each other without gaps.

So what I would like is either recommendation on hardware to handle the nail grid idea, a touchscreen module that ended flush with the actual screen on 2 sides (or a safe way to modify one) or a way to make a DIY XY sensor for multiple fingers.

Thank you very much in advance for your answers.