How to implement one-finger rotate gesture recognizer?

Question

I'm aware that there's the UIRotateGestureRecognizer already part of the iOS. But this gesture required two fingers. How I can implement a similar gesture recognizer requiring only one finger? There's a game in the AppStore - Gyrotate with a pretty good implementation of this. Any clues are appreciated. Thx.

Answer 1

Try exploring UIGestureRecognizer Class. You should be able to customize it using UIGestureRecognizerDelegate

Answer 2

Here's the code - it works on my simulator. Mark answered if that is what you were looking for.

    // On new touch, start a new array of points
- (void) touchesBegan:(NSSet *) touches withEvent:(UIEvent *) event
{
    self.points = [NSMutableArray array];
    CGPoint pt = [[touches anyObject] locationInView:self];
    [self.points addObject:[NSValue valueWithCGPoint:pt]];
}

// Add each point to the array
- (void) touchesMoved:(NSSet *) touches withEvent:(UIEvent *) event
{
    CGPoint pt = [[touches anyObject] locationInView:self];
    [self.points addObject:[NSValue valueWithCGPoint:pt]];
    [self setNeedsDisplay];
}

// At the end of touches, determine whether a circle was drawn
- (void) touchesEnded:(NSSet *) touches withEvent:(UIEvent *) event
{
    if (!self.points) return;
    if (self.points.count < 3) return;

    // Test 1: The start and end points must be between 60 pixels of each other
    CGRect tcircle;
    if (distance(POINT(0), POINT(self.points.count - 1)) < 60.0f)
        tcircle = [self centeredRectangle];

    // Test 2: Count the distance traveled in degrees. Must fall within 45 degrees of 2 PI
    CGPoint center = CGPointMake(CGRectGetMidX(tcircle), CGRectGetMidY(tcircle));
    float distance = ABS(acos(dotproduct(centerPoint(POINT(0), center), centerPoint(POINT(1), center))));
    for (int i = 1; i < (self.points.count - 1); i++)
        distance += ABS(acos(dotproduct(centerPoint(POINT(i), center), centerPoint(POINT(i+1), center))));
    if ((ABS(distance - 2 * M_PI) < (M_PI / 4.0f))) circle = tcircle;

    [self setNeedsDisplay];
}