Origami transition using CATransform3D perspective

Question

I'm trying to achieve a kind of origami transition on two UIView using only layer capabilities. The idea is to fold two views with a perspective effect. Both views have a perspective, the transition is defined by a rotation on each view, as well as a translation on one view such that this view seems to be attached to the other one.

The issue is that the view overlaps one another in the middle of the transition. I don't want to use a zPosition to visually avoid this overlapping, I really want these two views to act as if they were bound together by their shared side. Here is the code for the transition.

Any idea, or any other solution?

- (void)animateWithPerspective
{
    CGFloat rotationAngle = 90;
    CATransform3D transform = CATransform3DIdentity;
    UIView *topView;
    UIView *bottomView;
    UIView *mainView;
    CGRect frame;
    CGFloat size = 200;

    mainView = [[UIView alloc] initWithFrame:CGRectMake(10,10, size, size*2)];
    [self.view addSubview:mainView];
    bottomView = [[UIView alloc] initWithFrame:CGRectZero];
    bottomView.layer.anchorPoint = CGPointMake(0.5, 1);
    bottomView.frame = CGRectMake(0, size, size, size);
    bottomView.backgroundColor = [UIColor blueColor];
    [mainView addSubview:bottomView];

    topView = [[UIView alloc] initWithFrame:CGRectZero];
    topView.layer.anchorPoint = CGPointMake(0.5, 0);
    topView.frame = CGRectMake(0, 0, size, size);
    topView.backgroundColor = [UIColor redColor];
    [mainView addSubview:topView];

    transform.m34 = 1.0/700.0;
    topView.layer.transform = transform;
    bottomView.layer.transform = transform;

    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:2];
    [UIView setAnimationRepeatAutoreverses:YES];
    [UIView setAnimationRepeatCount:INFINITY];
    [UIView setAnimationCurve:UIViewAnimationCurveLinear];
    frame = bottomView.frame;
    frame.origin.y = bottomView.frame.origin.y - bottomView.frame.size.height - topView.frame.size.height;
    bottomView.frame = frame;
    topView.layer.transform = CATransform3DRotate(transform, rotationAngle * M_PI/180, 1, 0, 0);
    bottomView.layer.transform = CATransform3DRotate(transform, -rotationAngle * M_PI/180, 1, 0, 0);
    [UIView commitAnimations];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self animate];
}

To simplify the problem, let's get rid of any perspective transform. Here is a simpler code with the same kind of issue:

- (void)animateWithoutPerspective
{
    CGFloat rotationAngle = 90;
    UIView *topView;
    UIView *bottomView;
    UIView *mainView;
    CGRect frame;
    CGFloat size = 200;

    mainView = [[UIView alloc] initWithFrame:CGRectMake(10,10, size, size*2)];
    [self.view addSubview:mainView];
    bottomView = [[UIView alloc] initWithFrame:CGRectMake(0, size, size, size)];
    bottomView.backgroundColor = [UIColor blueColor];
    [mainView addSubview:bottomView];

    topView = [[UIView alloc] initWithFrame:CGRectZero];
    topView.layer.anchorPoint = CGPointMake(0.5, 0);
    topView.frame = CGRectMake(10, 0, size-20, size);
    topView.backgroundColor = [UIColor redColor];
    [mainView addSubview:topView];

    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:2];
    [UIView setAnimationRepeatAutoreverses:YES];
    [UIView setAnimationRepeatCount:INFINITY];
    [UIView setAnimationCurve:UIViewAnimationCurveLinear];
    frame = bottomView.frame;
    frame.origin.y = bottomView.frame.origin.y - bottomView.frame.size.height;
    bottomView.frame = frame;
    topView.layer.transform = CATransform3DMakeRotation(rotationAngle * M_PI/180, 1, 0, 0);
    [UIView commitAnimations];
}

Answer 1

To illustrate the answers.

I did not put all the animations and the perspective projection (the perspectiveLayer.sublayerTransform on its CATransformLayer subLayers). Play with the projection matrix m34 field value to see how it affects the vanishing point.