Multitouch gestures, built on MTIF.

Work in progress, but zooming and scrolling are functional.

This library doesn't assume much about gestures. It makes it easy to define your own gestures (see Custom Gestures below), and hook the provided ones into whatever system you want.

Use gestures by defining on-start, on-update and on-stop methods for whichever gesture you want. That's all, what you do with them is up to you. Each gesture class has different slots that you'll probably want to access.

Gesture: Two fingers moving horizontally or vertically.

Classes: cl-gestures:scroll-x and cl-gestures:scroll-y.

Slot: scroll-distance, starts at 0, increases as fingers move right.

Example:

;; Assuming we have getters and setters for the current x position...
(let ((initial-x))
  (defmethod on-start ((inst scroll-x))
    (declare (ignore inst))
    (setf initial-x (get-pos-x)))
  (defmethod on-update ((inst scroll-x))
    (with-slots (scroll-distance) inst
      (set-pos-x (+ scroll-distance initial-x)))))

Gesture: Two fingers moving apart.

Class: cl-gestures:zoom.

Slot: zoom, starts at 1.0, increases as fingers move apart.

Example:

(let ((initial-factor))
  (defmethod on-start ((inst zoom))
    (declare (ignore inst))
    (setf initial-factor (get-zoom)))
  (defmethod on-update ((inst zoom))
    (with-slots (zoom) inst
      (set-zoom (* initial-factor zoom)))))

Have a look at gestures_impl.lisp. The general idea is that gestures involve a number of fingers, and have three events associated with them: start, update, and stop. The gesture is 'started' as soon as the required number of fingers are present on the trackpad, gets 'updated' every time a new trackpad frame arrives, and is 'stopped' when the fingers are removed.

Currently this means fingers can be used for multiple gestures. This is a good thing, as, for example, it means you can scroll horizontally and vertically at the same time. If you don't want that behaviour, handle the state at a higher level.

The defgesture macro makes it easy to define simple gestures. For example, here is the scroll-y gesture:

(defgesture scroll-y
  "Two finger vertical scroll"
  :n-fingers 2
  :slots ((initial-y1 :initform 0)
          (initial-y2 :initform 0)
          (scroll-distance :initform 0))
  :start (lambda (f1 f2)
           (setf initial-y1 (mtif:finger-pos-y f1))
           (setf initial-y2 (mtif:finger-pos-y f2)))
  :update (lambda (f1 f2)
            (setf scroll-distance
                  (+ (- (mtif:finger-pos-y f1) initial-y1)
                     (- (mtif:finger-pos-y f2) initial-y2)))))

Key things to define

• the number of fingers required
• gesture-specific slots (properties)
• functions to be called when the gesture starts or updates

The :start and :update functions take n-fingers parameters, and have all gesture-specific slots exposed to them.

Some of the code here isn't necessarily tied to MTIF, and could be used with other trackpad drivers. If there's enough interest, this might happen one day.

zoom, scroll-x and scroll-y are should probably be renamed -- they actually define the gestures which are usually interpreted as zoom or scrolling, respectively. However they don't have to be. They'd be better named something like 'two-finger-spread' and 'two-finger-horiz/vert'.

MIT