How to handle autorotation in AVCaptureVideoPreviewLayer?

Question

My application supports all orientations except PortraitUpsideDown. In my view hierarchy I have an AVCaptureVideoPreviewLayer as a sublayer in the top view which is UIImageView. Then below it in view hierarchy are several overlay views showing controls.

Overlay views are working properly with orientation changes, but I don't how to be with this AVCaptureVideoPreviewLayer. I want it to behave like in Camera app, so that previewLayer stays still and controls are smoothly reorganized. Right now since the main view is rotated on orientation change, my preview layer is also rotated, which means that in landscape view it stays in portrait view, taking only part of the screen and the picture from camera being also rotated by 90 degrees. I've managed to rotate the preview layer manually, but then it has this orientation change animation, which leads to the background being seen for a while during the animation.

So what is the proper way to autorotate the controls while making previewLayer stay still?

Answer 1

In my implementation I have subclassed the UIView for my view which I want to rotate and something like viewController for this view which is just a subclass of NSObject.

In this viewController I do all the the checks related to changes of orientation, make decision if I should change orientation of my target view, and if yes, then I call method of my view for changing its orientation.

First of all we need to fix the orientation of whole application interface to Portrait mode, so that our ACCaptureVideoPreviewLayer always stays still. This is done in the MainViewController.h:

(BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation`
{
    return interfaceOrientation==UIInterfaceOrientationPortrait;
}

It returns NO to all orientations except Portrait.

In order to our custom viewController be able to track the changes of device orientation we need to make it an observer of corresponding notifications:

[[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(orientationChanged) name:UIDeviceOrientationDidChangeNotification object:nil];

I put these lines in the (void)awakeFromNib method of my viewController. So each time the device orientation is changed, the viewController's method orientationChanged will be called.

Its purpose is to check what is the new orientation of device, what was the last orientation of device and decide if to change it. Here is the implementation:

if(UIInterfaceOrientationPortraitUpsideDown==[UIDevice currentDevice].orientation ||
    lastOrientation==(UIInterfaceOrientation)[UIDevice currentDevice].orientation) 
    return;
    [[UIApplication sharedApplication]setStatusBarOrientation:[UIDevice currentDevice].orientation animated:NO];

    lastOrientation=[UIApplication sharedApplication].statusBarOrientation;
    [resultView orientationChanged];

If the orientation is the same as before or in PortraitUpsideDown then do nothing. Else it sets the status bar orientation to the proper one, so that when there is an incoming call or ossification, it will appear on the proper side of the screen. And then I call also method in the target view where all the corresponding changes for new orientation are done, like rotating, resizing, moving the other elements of interface in this view corresponding to the new orientation.

Here is the implementation of the orientationChanged in target view:

Float32 angle=0.f;
UIInterfaceOrientation orientation=[UIApplication sharedApplication].statusBarOrientation;

switch (orientation) {
    case UIInterfaceOrientationLandscapeLeft: 
        angle=-90.f*M_PI/180.f;
        break;
    case UIInterfaceOrientationLandscapeRight: 
            angle=90.f*M_PI/180.f;
        break;
    default: angle=0.f;
        break;
}   
if(angle==0 && CGAffineTransformIsIdentity(self.transform)) return;

CGAffineTransform transform=CGAffineTransformMakeRotation(angle);

[UIView beginAnimations:@"rotateView" context:nil];
[UIView setAnimationCurve:UIViewAnimationCurveEaseOut];
[UIView setAnimationDuration:0.35f];

self.transform=transform;

[UIView commitAnimations];

Of course here you can add any other changes like translation, scaling of different views of your interface that need to respond to new orientation and animate them.

Also you may not need the viewController for this, but do all just in the class of your view. Hope that the general idea is clear.

Also don't forget to stop getting notification for orientation changes when you don't need them like:

[[NSNotificationCenter defaultCenter]removeObserver:self name:UIDeviceOrientationDidChangeNotification object:nil];
[[UIDevice currentDevice]endGeneratingDeviceOrientationNotifications];

Answer 2

iOS 8 solution:

- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator {
    if ([UIApplication sharedApplication].statusBarOrientation == UIInterfaceOrientationLandscapeLeft) {
        self.layer.connection.videoOrientation = AVCaptureVideoOrientationLandscapeLeft;
    } else {
        self.layer.connection.videoOrientation = AVCaptureVideoOrientationLandscapeRight;
    }
}

in your setup code:

self.layer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.session];
self.layer.videoGravity = AVLayerVideoGravityResizeAspectFill;
if ([UIApplication sharedApplication].statusBarOrientation == UIInterfaceOrientationLandscapeLeft) {
    self.layer.connection.videoOrientation = AVCaptureVideoOrientationLandscapeLeft;
} else {
    self.layer.connection.videoOrientation = AVCaptureVideoOrientationLandscapeRight;
}