CALayer 的属性分析(几何及图层关系属性)

/** 先列举CALayer的属性(几何及图层关系属性) **/

/** Geometry and layer hierarchy properties. **/ /* The bounds of the layer. Defaults to CGRectZero. Animatable. */ @property CGRect bounds; /* The position in the superlayer that the anchor point of the layer's * bounds rect is aligned to. Defaults to the zero point. Animatable. */ @property CGPoint position; /* The Z component of the layer's position in its superlayer. Defaults * to zero. Animatable. */ @property CGFloat zPosition; /* Defines the anchor point of the layer's bounds rect, as a point in * normalized layer coordinates - '(0, 0)' is the bottom left corner of * the bounds rect, '(1, 1)' is the top right corner. Defaults to * '(0.5, 0.5)', i.e. the center of the bounds rect. Animatable. */ @property CGPoint anchorPoint; /* The Z component of the layer's anchor point (i.e. reference point for * position and transform). Defaults to zero. Animatable. */ @property CGFloat anchorPointZ; /* A transform applied to the layer relative to the anchor point of its * bounds rect. Defaults to the identity transform. Animatable. */ @property CATransform3D transform; /* Unlike NSView, each Layer in the hierarchy has an implicit frame * rectangle, a function of the `position', `bounds', `anchorPoint', * and `transform' properties. When setting the frame the `position' * and `bounds.size' are changed to match the given frame. */ @property CGRect frame; /* When true the layer and its sublayers are not displayed. Defaults to * NO. Animatable. */ @property(getter=isHidden) BOOL hidden;  

1.bounds

  为了描述子视图在父视图中的位置，需要一套坐标体系，layer.bounds.origin 属性提供了这套坐标体系，子视图的 layer.postion 即是用来描述子视图在父视图 bounds.origin 坐标系中的位置。(bounds.origin同父视图左上角是重合的)

2.position 和 anchorPoint

  如1.中所说，子视图在父视图中的位置，是相对父视图的坐标系(左上角)决定的，即是 子视图的anchorPoint 与 父视图坐标系的关系，其值为position。

  而锚点用的是比例值，取值0~1，在子视图size范围内取，默认(0.5,0.5)，例子如下图：

 如果如上图，position不变，改变锚点为(1.0,1.0)的话：

  So,  在父视图 bounds 确定后，子视图在父视图中的位置，是由 anchorPoint 和 position 共同确定的。

3.frame

  有了bounds描述一个视图世界中，视图的大小及视图与坐标系的关系(位置)；并且有了anchorPoint和position用于描述子视图与父视图世界坐标系的关系(位置)。

  我们其实还需要一个量，用来描述视图的大小及视图与在父视图世界中的位置，这就是frame：

  frame.origin.x = position.x - anchorPoint.x * bounds.size.width;

  frame.origin.y = position.y - anchorPoint.y * bounds.size.height;

  frame.size = bounds.size;

  为啥又有了这么个东西，太深层次我还没去看，我觉得可能是为了用起来方便吧。。。

4.有关3D的几个属性，后续会补上