如何获得正确的 z 排序 CATransform3D

Question

当我将围绕 y 轴的 CATransform3DRotate 应用到两个 UIView 时，它们的 z 顺序似乎颠倒了。 UIView 中已旋转回 z 轴的部分出现在已向屏幕旋转的部分的前面。这个动画说明了我的意思：

如何获得它以使 z 排序按预期运行？

我用来生成该动画的代码如下（双 [UIView animateWithDuration] 只需要正确地进行完整旋转）：

@interface ViewController ()

@property (strong, nonatomic) UIView *blueSquare;
@property (strong, nonatomic) UIView *redSquare;

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.blueSquare = [[UIView alloc] initWithFrame:(CGRect){.origin = {160,234}, .size = {400,300}}];
    self.blueSquare.backgroundColor = [UIColor blueColor];
    [self.view addSubview:self.blueSquare];

    self.redSquare = [[UIView alloc] initWithFrame:(CGRect){.origin = {464,234}, .size = {400,300}}];
    self.redSquare.backgroundColor = [UIColor redColor];
    [self.view addSubview:self.redSquare];
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];

    [UIView animateWithDuration:5 delay:0 options:UIViewAnimationOptionCurveLinear animations:^{
        CATransform3D transform = CATransform3DIdentity;

        transform.m34 = 1.0/900.0;  // for perspective

        transform = CATransform3DRotate(transform, M_PI, 0, 1, 0);

        self.blueSquare.layer.transform = transform;
        self.redSquare.layer.transform = transform;
    } completion:^(BOOL finished) {
        [UIView animateWithDuration:5 delay:0 options:UIViewAnimationOptionCurveLinear animations:^{
            CATransform3D transform = CATransform3DIdentity;

            transform.m34 = 1.0/900.0;  // for perspective

            transform = CATransform3DRotate(transform, 2*M_PI-0.001, 0, 1, 0);

            self.blueSquare.layer.transform = transform;
            self.redSquare.layer.transform = transform;
        } completion:nil];
    }];
}

@end

Answer 1

变换中的视角是相反的。通常，您会对变换的m34（变换矩阵中的第 3 列，第 4 行）分量使用负值。