iphone - Implement velocity in custom UIGestureRecognizer -

i have written custom uigesturerecognizer handles rotations 1 finger. designed work apples uirotationgesturerecognizer , return same values does.

now, implement velocity cannot figure out how apple defines , calculates velocity gesture recognizer. have idea how apple implements in uirotationgesturerecognizer?

you have keep reference of last touch position , it's timestamp.

double last_timestamp; cgpoint last_position; 

then like:

-(void) touchesbegan:(nsset *)touches withevent:(uievent *)event{      last_timestamp = cfabsolutetimegetcurrent();      uitouch *atouch = [touches anyobject];     last_position = [atouch locationinview: self]; }   -(void) touchesmoved:(nsset *)touches withevent:(uievent *)event {      double current_time = cfabsolutetimegetcurrent();      double elapsed_time = current_time - last_timestamp;      last_timestamp = current_time;      uitouch *atouch = [touches anyobject];     cgpoint location = [atouch locationinview:self.superview];      cgfloat dx = location.x - last_position.x;     cgfloat dy = location.y - last_position.y;      cgfloat path_travelled = sqrt(dx*dx+dy*dy);      cgfloat sime_kind_of_velocity = path_travelled/elapsed_time;      nslog (@"v=%.2f", sime_kind_of_velocity);      last_position = location; } 

this should give kind of speed reference.