MacBook Multitouch

Here's code to read the raw gesture data from a MacBook trackpad.

[Update: if you're on a MacBook with Java enabled, you can try the demo applet]

If you use this to make something fun, please let me know and I'll post it here...

Notes about the fields of the Finger struct:

identifier

Persistent identifier for each touch -- each "finger" may move around the Fingers[] array, but this will remain the same.

normalized.pos.x

Current position, from [0..1]

size

Close to zero if you're barely touching the touch pad

angle, majorAxis, minorAxis

Describes the ellipsoid of your finger. Yes, you can track rotation of a single finger!

#include <math.h>
#include <unistd.h>
#include <CoreFoundation/CoreFoundation.h>

typedef struct { float x,y; } mtPoint;
typedef struct { mtPoint pos,vel; } mtReadout;

typedef struct {
  int frame;
  double timestamp;
  int identifier, state, foo3, foo4;
  mtReadout normalized;
  float size;
  int zero1;
  float angle, majorAxis, minorAxis; // ellipsoid
  mtReadout mm;
  int zero2[2];
  float unk2;
} Finger;

typedef void *MTDeviceRef;
typedef int (*MTContactCallbackFunction)(int,Finger*,int,double,int);

MTDeviceRef MTDeviceCreateDefault();
void MTRegisterContactFrameCallback(MTDeviceRef, MTContactCallbackFunction);
void MTDeviceStart(MTDeviceRef, int); // thanks comex


int callback(int device, Finger *data, int nFingers, double timestamp, int frame) {
  for (int i=0; i<nFingers; i++) {
    Finger *f = &data[i];
    printf("Frame %7d: Angle %6.2f, ellipse %6.3f x%6.3f; "
    	   "position (%6.3f,%6.3f) vel (%6.3f,%6.3f) "
    	   "ID %d, state %d [%d %d?] size %6.3f, %6.3f?\n",
	   f->frame,
	   f->angle * 90 / atan2(1,0),
	   f->majorAxis,
	   f->minorAxis,
	   f->normalized.pos.x,
	   f->normalized.pos.y,
	   f->normalized.vel.x,
	   f->normalized.vel.y,
	   f->identifier, f->state, f->foo3, f->foo4,
	   f->size, f->unk2);
  }
  printf("\n");
  return 0;
}

int main() {
  MTDeviceRef dev = MTDeviceCreateDefault();
  MTRegisterContactFrameCallback(dev, callback);
  MTDeviceStart(dev, 0);
  printf("Ctrl-C to abort\n");
  sleep(-1);
  return 0;
}

run: test
	./test
test: test.m
	gcc -F/System/Library/PrivateFrameworks -framework MultitouchSupport $^ -o $@ -std=c99

MTRegisterContactFrameCallback(dev, callback);