版本记录

版本号	时间
V1.0	2018.01.17

前言

CAShapeLayer类是我们经常用到的类，平时也就用一下其基本用法，但是很少详细的翻出来它的开发文档仔细研究下，下面，我就带领大家详细的研究下这个类，详细的看一下它的用法。

API文档

这个类继承自CALayer，属于QuartzCore框架的类，下面我们就先看一下它的API。

/* CoreAnimation - CAShapeLayer.h

   Copyright (c) 2008-2017, Apple Inc.
   All rights reserved. */

#import 

NS_ASSUME_NONNULL_BEGIN

/* The shape layer draws a cubic Bezier spline in its coordinate space.
 *
 * The spline is described using a CGPath object and may have both fill
 * and stroke components (in which case the stroke is composited over
 * the fill). The shape as a whole is composited between the layer's
 * contents and its first sublayer.
 *
 * The path object may be animated using any of the concrete subclasses
 * of CAPropertyAnimation. Paths will interpolate as a linear blend of
 * the "on-line" points; "off-line" points may be interpolated
 * non-linearly (e.g. to preserve continuity of the curve's
 * derivative). If the two paths have a different number of control
 * points or segments the results are undefined.
 *
 * The shape will be drawn antialiased, and whenever possible it will
 * be mapped into screen space before being rasterized to preserve
 * resolution independence. (However, certain kinds of image processing
 * operations, e.g. CoreImage filters, applied to the layer or its
 * ancestors may force rasterization in a local coordinate space.)
 *
 * Note: rasterization may favor speed over accuracy, e.g. pixels with
 * multiple intersecting path segments may not give exact results. */

CA_CLASS_AVAILABLE (10.6, 3.0, 9.0, 2.0)
@interface CAShapeLayer : CALayer

/* The path defining the shape to be rendered. If the path extends
 * outside the layer bounds it will not automatically be clipped to the
 * layer, only if the normal layer masking rules cause that. Upon
 * assignment the path is copied. Defaults to null. Animatable.
 * (Note that although the path property is animatable, no implicit
 * animation will be created when the property is changed.) */

@property(nullable) CGPathRef path;

/* The color to fill the path, or nil for no fill. Defaults to opaque
 * black. Animatable. */

@property(nullable) CGColorRef fillColor;

/* The fill rule used when filling the path. Options are `non-zero' and
 * `even-odd'. Defaults to `non-zero'. */

@property(copy) NSString *fillRule;

/* The color to fill the path's stroked outline, or nil for no stroking.
 * Defaults to nil. Animatable. */

@property(nullable) CGColorRef strokeColor;

/* These values define the subregion of the path used to draw the
 * stroked outline. The values must be in the range [0,1] with zero
 * representing the start of the path and one the end. Values in
 * between zero and one are interpolated linearly along the path
 * length. strokeStart defaults to zero and strokeEnd to one. Both are
 * animatable. */

@property CGFloat strokeStart;
@property CGFloat strokeEnd;

/* The line width used when stroking the path. Defaults to one.
 * Animatable. */

@property CGFloat lineWidth;

/* The miter limit used when stroking the path. Defaults to ten.
 * Animatable. */

@property CGFloat miterLimit;

/* The cap style used when stroking the path. Options are `butt', `round'
 * and `square'. Defaults to `butt'. */

@property(copy) NSString *lineCap;

/* The join style used when stroking the path. Options are `miter', `round'
 * and `bevel'. Defaults to `miter'. */

@property(copy) NSString *lineJoin;

/* The phase of the dashing pattern applied when creating the stroke.
 * Defaults to zero. Animatable. */

@property CGFloat lineDashPhase;

/* The dash pattern (an array of NSNumbers) applied when creating the
 * stroked version of the path. Defaults to nil. */

@property(nullable, copy) NSArray *lineDashPattern;

@end

/* `fillRule' values. */

CA_EXTERN NSString *const kCAFillRuleNonZero
    CA_AVAILABLE_STARTING (10.6, 3.0, 9.0, 2.0);
CA_EXTERN NSString *const kCAFillRuleEvenOdd
    CA_AVAILABLE_STARTING (10.6, 3.0, 9.0, 2.0);

/* `lineJoin' values. */

CA_EXTERN NSString *const kCALineJoinMiter
    CA_AVAILABLE_STARTING (10.6, 3.0, 9.0, 2.0);
CA_EXTERN NSString *const kCALineJoinRound
    CA_AVAILABLE_STARTING (10.6, 3.0, 9.0, 2.0);
CA_EXTERN NSString *const kCALineJoinBevel
    CA_AVAILABLE_STARTING (10.6, 3.0, 9.0, 2.0);

/* `lineCap' values. */

CA_EXTERN NSString *const kCALineCapButt
    CA_AVAILABLE_STARTING (10.6, 3.0, 9.0, 2.0);
CA_EXTERN NSString *const kCALineCapRound
    CA_AVAILABLE_STARTING (10.6, 3.0, 9.0, 2.0);
CA_EXTERN NSString *const kCALineCapSquare
    CA_AVAILABLE_STARTING (10.6, 3.0, 9.0, 2.0);

NS_ASSUME_NONNULL_END

Overview

在其坐标空间中绘制三次Bezier样条曲线的图层。

shape是在图层内容和第一个子图层之间合成的。

shape将被绘制反锯齿，并且在可能的情况下将被映射到屏幕空间，然后进行光栅化以保持分辨率的独立性。但是，应用于图层或其父类的某些图像处理操作（如CoreImage滤镜）可能会强制在本地坐标空间中进行光栅化。

注意：与精度相比，Shape光栅化可能更有利于速度。例如，具有多个相交路径段的像素可能不会给出确切的结果。

shape layer在其坐标空间中绘制一个三次贝塞尔样条曲线。

样条曲线使用CGPath对象进行描述，并可能同时填充和描边组件（在这种情况下描边被合成填充）。整个形状是在图层之间合成的内容及其第一个子层。

路径对象可以使用任何具体的CAPropertyAnimation的子类来动画。路径将作为线性混合插值"on-line"点; 可以非线性地插入"off-line"点（例如保持曲线衍生物的连续性）。如果两个路径有不同的控制数量点或段的结果是不确定的。

Topics

1. Specifying the Shape Path

path
- 定义要呈现的形状的路径，可动画。

2. Accessing Shape Style Properties

fillColor
- 用于填充形状路径的颜色，可动画。
fillRule
- 填充形状路径时使用的填充规则。
lineCap
- 指定形状路径的线条样式。
lineDashPattern
- 描边时，虚线图案应用于形状的路径。
lineDashPhase
- 描边时，应用于形状的路径描边阶段，可动画。
lineJoin
- 指定形状路径的线条连接样式。
lineWidth
- 指定形状路径的线宽，可动画。
miterLimit
- 描边形状路径时使用的尖角限制，可动画。
strokeColor
- 用于描绘形状路径的颜色，可动画。
strokeStart
- 开始描边路径的相对位置，可动画。
strokeEnd
- 停止描边路径的相对位置，可动画。

3. Constants

Shape Fill Mode Values
- 这些常量指定fillRule的可能填充模式。
Line Join Values
- 这些常量指定描边路径的连接段之间的连接点的形状。图lineJoin. Figure 1显示了线条连接样式的外观。

Line Cap Values
- 这些常量指定描边时开放路径的端点形状。图 lineCap.Figure 1显示了线帽样式的外观。

后记

下一篇将主要介绍CAShapeLayer的基本使用。

CAShapeLayer类解析（一） —— 基本概览