MTIF

This is a Common Lisp interface to the Apple multitouch trackpad.

Usage:

• (mtif:start #'callback-fn) to start getting touch data.
• (mtif:stop) to stop getting data!

Calling #'start spawns a thread which repeatedly calls #'callback-fn, passing the latest "frame" of multitouch data. No processing is done -- you'll just get a list of finger data at each frame. If you want gesture recognition, watch this repo.

Example: https://github.com/rmhsilva/mtif/tree/master/examples.

Data Format

An example callback function:

(defun print-all-touches (finger-data timestamp frame)
  "Example callback which just prints all touches to *standard-output*"
  (format t "~A [~{~A~%  ~}]~%" (length finger-data) finger-data))

The finger data struct has the following slots:

  id                 -- Numeric identifier for this finger
  state              -- The finger state
  size               -- A measure of the area covered
  pos-x              -- Normalised X position, 
  pos-y              -- Normalised Y position
  vel-x              -- Normalised X velocity
  vel-y              -- Normalised Y velocity
  ellipse-angle      -- Angle of the finger ellipsoid
  ellipse-major-axis -- Major axis of the finger ellipsoid
  ellipse-minor-axis -- Minor axis of the finger ellipsoid

Coordinate System

Positions (pos-x and pos-y) have the origin in the bottom left corner:

    (0,1)              (1,1)
        +--------------+
        |              |
        |   trackpad   |
        |              |
        +--------------+
    (0,0)              (1,0)

The ellipse angle takes a value in the interval [0, pi] radians, where 0 radians means the finger is angled to right right hand edge of the trackpad:

              pi/2
               ^
               |
               |
      pi ------|------> 0 rad
               |
               |
              pi/2

Background Info

This uses the "private" (undocumented) MacOS MultiTouch framework. See https://gist.github.com/rmhsilva/61cc45587ed34707da34818a76476e11 for more info.

License

MIT