GGDraggableView.m

- (void)dragged:(UIPanGestureRecognizer *)gestureRecognizer
{
    CGFloat xDistance = [gestureRecognizer translationInView:self].x;
    CGFloat yDistance = [gestureRecognizer translationInView:self].y;

    switch (gestureRecognizer.state) {
        case UIGestureRecognizerStateBegan:{
            self.originalPoint = self.center;
            break;
        };
        case UIGestureRecognizerStateChanged:{
            CGFloat rotationStrength = MIN(xDistance / 320, 1);
            CGFloat rotationAngel = (CGFloat) (2*M_PI/16 * rotationStrength);
            CGFloat scaleStrength = 1 - fabsf(rotationStrength) / 4;
            CGFloat scale = MAX(scaleStrength, 0.93);
            CGAffineTransform transform = CGAffineTransformMakeRotation(rotationAngel);
            CGAffineTransform scaleTransform = CGAffineTransformScale(transform, scale, scale);
            self.transform = scaleTransform;
            self.center = CGPointMake(self.originalPoint.x + xDistance, self.originalPoint.y + yDistance);

            [self updateOverlay:xDistance];

            break;
        };
        case UIGestureRecognizerStateEnded: {
            [self resetViewPositionAndTransformations];
            break;
        };
        case UIGestureRecognizerStatePossible:break;
        case UIGestureRecognizerStateCancelled:break;
        case UIGestureRecognizerStateFailed:break;
    }
}

- (void)updateOverlay:(CGFloat)distance
{
    if (distance > 0) {
        self.overlayView.mode = GGOverlayViewModeRight;
    } else if (distance <= 0) {
        self.overlayView.mode = GGOverlayViewModeLeft;
    }
    CGFloat overlayStrength = MIN(fabsf(distance) / 100, 0.4);
    self.overlayView.alpha = overlayStrength;
}

- (void)resetViewPositionAndTransformations
{
    [UIView animateWithDuration:0.2
                     animations:^{
        self.center = self.originalPoint;
        self.transform = CGAffineTransformMakeRotation(0);
        self.overlayView.alpha = 0;
    }];
}