在iOS上，为什么设置图层的sublayerTransform会使其自身像CATranformLayer一样？ [英] On iOS, why does setting a layer's sublayerTransform turn itself to act like CATranformLayer?

问题描述

众所周知，图层的 zPosition 只能确定哪一层覆盖了哪一层。是否为 zPosition 为10或1000不会影响其位置。

即使我们。这正是 sublayerTransform 的工作方式：仅转换内容，而不转换电视本身。

现在，如果我使用 transform 而不是 sublayerTranform ，它会是什么样子？ ？想象一下，不要只转换内容，而是将整个电视与附加到屏幕上的内容一起旋转，你会看到预期的结果：

所以，是的，显然转换和 sublayerTransform 虽然 zPosition 时表现却完全不同Conceptual / CoreAnimation_guide / CoreAnimationBasics / CoreAnimationBasics.html＃// apple_ref / doc / uid / TP40004514-CH2-SW18rel =nofollow noreferrer>文档没有明确说明。子图层的 zPosition 对其父级的转换没有影响，但确实对其父级的<$ c $提供了正常的3D效果c> sublayerTransform 。

It is known that the zPosition of the layers only determines which layer cover up which layer. Whether it is a zPosition of 10 or 1000 won't affect its position.

That is, unless if we use CATransformLayer to contain those layers, then the zPosition of those layers will affect the layers' position.

However, the following code running in iOS 5.1.1 does make the zPosition alter the position of the layers... you can try it in a new Single View App, and add the following code to ViewController.m. If the zPosition of layer2 is changed from 88 to 188, we can see that the layer moves accordingly. So no CATransformLayer is in the code; why will it behave like that? (Please quote Apple docs or any reference).

Also related is, if the line self.view.layer.sublayerTransform = transform3D; is changed to self.view.layer.transform = transform3D; then the zPosition will have no effect on the position. But according to the Apple docs, transform and sublayerTransform only differ in whether self is transformed or not:

Two layer properties specify transform matrices: transform and sublayerTransform. The matrix specified by the transform property is applied to the layer and its sublayers relative to the layer's anchorPoint. [...] The matrix specified by the sublayerTransform property is applied only to the layer’s sublayers, rather than to the layer itself.

So it is strange that why changing that will cause self.view.layer to act like a CATransformLayer.

-(void) viewDidAppear:(BOOL)animated {

    CATransform3D transform3D = CATransform3DIdentity;

    transform3D.m34 = -1.0 / 1000;

    transform3D = CATransform3DRotate(transform3D, M_PI / 4, 0, 1, 0);

    self.view.layer.sublayerTransform = transform3D;

    CALayer *layer1 = [[CALayer alloc] init];
    layer1.zPosition = 33;
    layer1.frame = CGRectMake(100, 100, 100, 100);
    layer1.backgroundColor = [[UIColor orangeColor] CGColor];

    [self.view.layer addSublayer:layer1];

    CALayer *layer2 = [[CALayer alloc] init];
    layer2.zPosition = 88;
    layer2.frame = CGRectMake(100, 120, 100, 100);
    layer2.backgroundColor = [[UIColor yellowColor] CGColor];

    [self.view.layer addSublayer:layer2];    

}

解决方案

To really understand the difference between a layer transform and sublayerTransform properties, I think it is useful to think of this in terms of looking at a TV with 3D content in it. Check out my modified version of your code in Swift playground.

Here's the beginning version: you have a TV with content consisting of no perspective transformation whatsoever. Therefore, your content (the two orange and yellow sublayers) looks flat even with rotation around the y-axis. Pretty much what you'd expect for an orthographic projection.

However, if you hold your TV still, but transform your content underneath with perspective projection, now you immediately see the depth of your content. The zPosition of the sublayers you added truly play an important part in giving you a sense of depth, and it is rightfully so by its definition. This is exactly how sublayerTransform works: transform only the contents, but not the TV itself.

Now, what would it look like if I use transform instead of sublayerTranform? Imagine not transforming just the contents, but rotate the entire TV along with the contents attached to the screen, and you'd see the expected result:

So, yeah, apparently transform and sublayerTransform behave quite differently when it comes to treating zPosition of the sublayers, although the documentation doesn't explicitly say so. A sublayer's zPosition has no effect on its parent's transform, but does provide normal 3D effect on its parent's sublayerTransform.

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