You could have some "horizontal" direction detection if the x
component was some reasonable multiple of the y
component. So, perhaps if x
was five times y
, that could be considered horizontal swipe. And vice versa for vertical. Whether five is the right multiple is up to you (using tan-1, you can see that translates to roughly 11.3° from absolute horizontal/vertical), but it's conceptually one way to tackle it easily.
For example, here's a gesture recognizer that will send a camera a command to initiate movement in a particular direction when the user starts a swipe in that direction, and will tell the camera to stop when the user lifts their finger off the screen:
CGFloat const gestureMinimumTranslation = 20.0;
typedef enum : NSInteger {
kCameraMoveDirectionNone,
kCameraMoveDirectionUp,
kCameraMoveDirectionDown,
kCameraMoveDirectionRight,
kCameraMoveDirectionLeft
} CameraMoveDirection;
@interface ViewController ()
{
CameraMoveDirection direction;
}
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
UIPanGestureRecognizer *recognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipe:)];
[self.viewWithGestureRecognizer addGestureRecognizer:recognizer];
}
// This is my gesture recognizer handler, which detects movement in a particular
// direction, conceptually tells a camera to start moving in that direction
// and when the user lifts their finger off the screen, tells the camera to stop.
- (void)handleSwipe:(UIPanGestureRecognizer *)gesture
{
CGPoint translation = [gesture translationInView:self.view];
if (gesture.state == UIGestureRecognizerStateBegan)
{
direction = kCameraMoveDirectionNone;
}
else if (gesture.state == UIGestureRecognizerStateChanged && direction == kCameraMoveDirectionNone)
{
direction = [self determineCameraDirectionIfNeeded:translation];
// ok, now initiate movement in the direction indicated by the user's gesture
switch (direction) {
case kCameraMoveDirectionDown:
NSLog(@"Start moving down");
break;
case kCameraMoveDirectionUp:
NSLog(@"Start moving up");
break;
case kCameraMoveDirectionRight:
NSLog(@"Start moving right");
break;
case kCameraMoveDirectionLeft:
NSLog(@"Start moving left");
break;
default:
break;
}
}
else if (gesture.state == UIGestureRecognizerStateEnded)
{
// now tell the camera to stop
NSLog(@"Stop");
}
}
// This method will determine whether the direction of the user's swipe
- (CameraMoveDirection)determineCameraDirectionIfNeeded:(CGPoint)translation
{
if (direction != kCameraMoveDirectionNone)
return direction;
// determine if horizontal swipe only if you meet some minimum velocity
if (fabs(translation.x) > gestureMinimumTranslation)
{
BOOL gestureHorizontal = NO;
if (translation.y == 0.0)
gestureHorizontal = YES;
else
gestureHorizontal = (fabs(translation.x / translation.y) > 5.0);
if (gestureHorizontal)
{
if (translation.x > 0.0)
return kCameraMoveDirectionRight;
else
return kCameraMoveDirectionLeft;
}
}
// determine if vertical swipe only if you meet some minimum velocity
else if (fabs(translation.y) > gestureMinimumTranslation)
{
BOOL gestureVertical = NO;
if (translation.x == 0.0)
gestureVertical = YES;
else
gestureVertical = (fabs(translation.y / translation.x) > 5.0);
if (gestureVertical)
{
if (translation.y > 0.0)
return kCameraMoveDirectionDown;
else
return kCameraMoveDirectionUp;
}
}
return direction;
}
@end
This demonstrates how you could determine the initial direction of a pan gesture and then act once the initial direction is established, as well as upon the end of the gesture.