orientation.m

- (UIInterfaceOrientation)orientationByTransforming:(CGAffineTransform)transform fromOrientation:(UIInterfaceOrientation)c
{
    CGFloat angle = atan2f(transform.b, transform.a);
    NSInteger multiplier = (NSInteger)roundf(angle / M_PI_2);
    UIInterfaceOrientation orientation = self.interfaceOrientation;
    
    if (multiplier < 0) {
        // clockwise rotation
        while (multiplier++ < 0) {
            switch (orientation) {
                case UIInterfaceOrientationPortrait:
                    orientation = UIInterfaceOrientationLandscapeLeft;
                    break;
                case UIInterfaceOrientationLandscapeLeft:
                    orientation = UIInterfaceOrientationPortraitUpsideDown;
                    break;
                case UIInterfaceOrientationPortraitUpsideDown:
                    orientation = UIInterfaceOrientationLandscapeRight;
                    break;
                case UIInterfaceOrientationLandscapeRight:
                    orientation = UIInterfaceOrientationPortrait;
                    break;
                default:
                    break;
            }
        }
    }
    else if (multiplier > 0) {
        // counter-clockwise rotation
        while (multiplier-- > 0) {
            switch (orientation) {
                case UIInterfaceOrientationPortrait:
                    orientation = UIInterfaceOrientationLandscapeRight;
                    break;
                case UIInterfaceOrientationLandscapeRight:
                    orientation = UIInterfaceOrientationPortraitUpsideDown;
                    break;
                case UIInterfaceOrientationPortraitUpsideDown:
                    orientation = UIInterfaceOrientationLandscapeLeft;
                    break;
                case UIInterfaceOrientationLandscapeLeft:
                    orientation = UIInterfaceOrientationPortrait;
                    break;
                default:
                    break;
            }
        }
    }

    return (UIInterfaceOrientation)orientation;
}