1. 画弧线

坐标系:

// 添加一条弧线，会从endAngle对应的点画到startAngle，1-顺时针画，0-逆时针画
CGContextAddArc(ctx, x, y, raidus, startAngle, endAngle  , 1);

// UIBezierPath 会从startAngle的点画向endAngle的点
UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:center radius:newDadius startAngle:startAngle endAngle:endAngle clockwise:YES];

例如：

CGContextAddArc(ctx, center.x, center.y, 150, 0, M_PI  , 0);

结果：

Paste_Image.png

使用以上两种画弧度的方法画出的线(即下面图中的表盘的线，实际为一段弧度很小、宽度较大的弧线)，假设lineWidth为10，则都会以圆周为中心，在圆周外侧和内侧分别画5（画弧度时，尽量不要把线断点类型lineCap设置成Round，否则可能变成画出圆）：

如果要都画在对应的圆周内，需要修改radius参数(newRadius = radius - lineWidth * 0.5)以达到效果:

2.虚线的相位(phase)和样式patten

CGContextSetLineDash(<#CGContextRef  _Nullable c#>, <#CGFloat phase#>, <#const CGFloat * _Nullable lengths#>, <#size_t count#>)

patten是一组CGFloat数组，用来描述画线时 需要画线的长度和画空白的长度，如{10, 10} 说明画线时，先画10的线段，然后画10的空白，以此反复；如果是数组元素个数是单数，如{10, 5, 10}， 则先画10的线，再空白5，再画10，空白10，画5，再空白10，以此反复。
而相位phase则用来指明最开始要先跳过多少长度不画（包括pattern中画线与画空白的部分），如一条pattern为{10，10}的虚线，相位为0时，先画10，再画10 的空白，以此反复

相位为5时，会跳过5（原来要画线的10中的5），所以是先画5，然后画10的空白，再画10的线，空白10，反复：

相位为10时，先跳过10（原要先画的长度10中的10），所以先画10的空白，再按pattern反复

相位为15时，先跳过15（画线的10+画空白的5），所以先画5的空白，再按pattern反复

3.CAGradientLayer属性

colors 渐变色

/* The array of CGColorRef objects defining the color of each gradient
 * stop. Defaults to nil. Animatable. */

@property(nullable, copy) NSArray *colors; 

gradient.colors = @[
                        (id)[UIColor blackColor].CGColor,
                        (id)[UIColor orangeColor].CGColor,
                        (id)[UIColor redColor].CGColor
                        ];

locations 位置

/* An optional array of NSNumber objects defining the location of each
 * gradient stop as a value in the range [0,1]. The values must be
 * monotonically increasing. If a nil array is given, the stops are
 * assumed to spread uniformly across the [0,1] range. When rendered,
 * the colors are mapped to the output colorspace before being
 * interpolated. Defaults to nil. Animatable. */

location数组元素必须和colors相同，值在 [ 0 , 1 ] 间且必须是单调递增的，locations表示颜色渐变的位置，如colors = @[red, green, blue],locations = @[@0.3, @0.5, @0.7],表示[ 0, 0.3] 为正红色, [0.5]为正绿色，[0.7, 1]为正蓝色，[0,3 , 0.5] 为红色到绿色的渐变，[0.5, 0.7] 为绿色到蓝色的渐变：

startPoint、endPoint

/* The start and end points of the gradient when drawn into the layer's
 * coordinate space. The start point corresponds to the first gradient
 * stop, the end point to the last gradient stop. Both points are
 * defined in a unit coordinate space that is then mapped to the
 * layer's bounds rectangle when drawn. (I.e. [0,0] is the bottom-left
 * corner of the layer, [1,1] is the top-right corner.) The default values
 * are [.5,0] and [.5,1] respectively. Both are animatable. */

@property CGPoint startPoint;
@property CGPoint endPoint;

startPoint、endPoint表示颜色渐变的方向，{ x , y } 取值为[0 , 1]，是相对于layer.bounds的，[0 , 0]是左上角，[1 , 1]是右下角。startPoint默认是[0.5 , 0]，endPoint默认是[0.5 , 1]:

4.CAReplicatorLayer

快速创建重复layer，可以改变重复layer的transform、RGBA。
Note: CAReplicatorLayer中的instanceTransform 是根据前一个自图层的状态，以CAReplicatorLayer的anchorPoint（而不是前一个layer的anchorPoint）来做变换的。一个图层如果翻转后，坐标系也会跟随着翻转，例如一个图层绕X轴旋转180°后，增加其Y坐标图层会往屏幕上方移动，与原坐标系中Y值的改变相反。

基础：

    CAReplicatorLayer *replicator = [CAReplicatorLayer layer];
    replicator.frame = self.containerView.bounds;
    [self.containerView.layer addSublayer:replicator];
    
    //configure the replicator
    replicator.instanceCount = 20;
    
    //apply a transform for each instance
    CATransform3D transform = CATransform3DIdentity;
    transform = CATransform3DRotate(transform, M_PI / 10.0, 0, 0, 1);
    replicator.instanceTransform = transform;
    
    //apply a color shift for each instance
    replicator.instanceBlueOffset = -0.1;
    replicator.instanceGreenOffset = -0.1;
    
    //create a sublayer and place it inside the replicator
    CALayer *layer = [CALayer layer];
    layer.frame = CGRectMake(137.5f, 25.0f, 25.0f, 25.0f);
    layer.backgroundColor = [UIColor whiteColor].CGColor;
    [replicator addSublayer:layer];

效果：

CAReplicatorLayer + CoreAnimation

Example1：

func animation1() {
        // create CAReplicatorLayer
        let replicator = CAReplicatorLayer()
        replicator.bounds = CGRect(x: 0.0, y: 0.0, width: 60.0, height: 60.0)
        replicator.position = view.center
        replicator.backgroundColor = UIColor.lightGrayColor().CGColor
        view.layer.addSublayer(replicator)
        
        // creat Sublayer
        let bar = CALayer()
        bar.bounds = CGRect(x: 0.0, y: 0.0, width: 8.0, height: 40.0)
        bar.position = CGPoint(x: 10.0, y: 75.0)
        bar.cornerRadius = 2.0;
        bar.backgroundColor = UIColor.redColor().CGColor
        
        replicator.addSublayer(bar)
        
        // create Animation for bar
        let move = CABasicAnimation(keyPath: "position.y")
        move.toValue = bar.position.y - 35.0
        move.duration = 0.5
        move.autoreverses = true
        move.repeatCount = Float.infinity
        bar .addAnimation(move, forKey: nil)
        
        // config replicator
        replicator.instanceCount = 3
        replicator.instanceTransform = CATransform3DMakeTranslation(20.0, 0, 0)
        replicator.instanceDelay = CFTimeInterval(0.33)
        replicator.masksToBounds = true
    }

效果：

Example 2：

 // create the CAReplicatorLayer
        let replicator = CAReplicatorLayer()
        replicator.bounds = CGRect(x: 0, y: 0, width: 200, height: 200)
        replicator.cornerRadius = 10.0
        replicator.backgroundColor = UIColor(white: 0.0, alpha: 0.75).CGColor
        replicator.position = view.center
        view.layer .addSublayer(replicator)
        
        // create a dot
        let dot = CALayer()
        dot.bounds = CGRect(x: 0, y: 0, width: 14, height: 14)
        dot.position = CGPoint(x: 100, y: 40)
        dot.backgroundColor = UIColor(white: 0.8, alpha: 1.0).CGColor
        dot.borderColor = UIColor(white: 1.0, alpha: 1.0).CGColor
        dot.borderWidth = 1.0
        dot.cornerRadius = 2.0
        // fix 第一次循环时所有点大小一样的不自然状态
        dot.transform = CATransform3DMakeScale(0.01, 0.01, 0.01)
        replicator.addSublayer(dot)
        
        // create animation
        let shrink = CABasicAnimation(keyPath: "transform.scale")
        shrink.fromValue = 1.0
        shrink.toValue = 0.1
        shrink.duration = 1.5
        // 不能开启autoReverse，一次循环后dot须正好在最大状态保证动画看起来正常
        shrink.autoreverses = false
        shrink.repeatCount = Float.infinity
        dot.addAnimation(shrink, forKey: nil)
        
        // config replicaotr
        replicator.instanceCount = 15
        replicator.instanceTransform = CATransform3DMakeRotation(CGFloat(M_PI * 2) / CGFloat(replicator.instanceCount), 0, 0, 1)
        replicator.instanceDelay = shrink.duration / CFTimeInterval(replicator.instanceCount)

效果：

Example 3：

func animation3() {
        // create the CAReplicatorLayer
        let replicator = CAReplicatorLayer()
        replicator.bounds = view.bounds
        replicator.backgroundColor = UIColor(white: 0, alpha: 0.75).CGColor
        replicator.position = view.center
        view.layer.addSublayer(replicator)
        
        // ceate a dot
        let dot = CALayer()
        dot.bounds = CGRect(x: 0, y: 0, width: 10, height: 10)
        dot.position = CGPointMake(31.5, 71.5)
        dot.backgroundColor = UIColor(white: 0.8, alpha: 1.0).CGColor
        dot.borderColor = UIColor(white: 1.0, alpha: 1.0).CGColor
        dot.borderWidth = 1
        dot.cornerRadius = 5.0
        dot.shouldRasterize = true
        dot.rasterizationScale = UIScreen.mainScreen().scale
        replicator.addSublayer(dot)
        
        // create an animation
        let move = CAKeyframeAnimation(keyPath: "position")
        move.path = getAPath()
        move.repeatCount = Float.infinity
        move.duration = 4.0
        dot.addAnimation(move, forKey: nil)
        
        // config replicator
        replicator.instanceCount = 20
        replicator.instanceDelay = 0.1
        replicator.instanceColor = UIColor(red: 0, green: 1, blue: 0, alpha: 1).CGColor
        replicator.instanceGreenOffset = -0.03
    }
    
    func getAPath() -> CGPath {
        let bezierPath = UIBezierPath()
        bezierPath.moveToPoint(CGPointMake(31.5, 71.5))
        bezierPath.addLineToPoint(CGPointMake(31.5, 23.5))
        
        bezierPath.addCurveToPoint(CGPointMake(58.5, 38.5),
            controlPoint1: CGPointMake(31.5, 23.5),
            controlPoint2: CGPointMake(62.46, 18.69))
        
        bezierPath.addCurveToPoint(CGPointMake(53.5, 45.5),
            controlPoint1: CGPointMake(57.5, 43.5),
            controlPoint2: CGPointMake(53.5, 45.5))
        
        bezierPath.addLineToPoint(CGPointMake(43.5, 48.5))
        bezierPath.addLineToPoint(CGPointMake(53.5, 66.5))
        bezierPath.addLineToPoint(CGPointMake(62.5, 51.5))
        bezierPath.addLineToPoint(CGPointMake(70.5, 66.5))
        bezierPath.addLineToPoint(CGPointMake(86.5, 23.5))
        bezierPath.addLineToPoint(CGPointMake(86.5, 78.5))
        bezierPath.addLineToPoint(CGPointMake(31.5, 78.5))
        bezierPath.addLineToPoint(CGPointMake(31.5, 71.5))
        bezierPath.closePath()
        
        var t = CGAffineTransformMakeScale(3.0, 3.0)
        return CGPathCreateCopyByTransformingPath(bezierPath.CGPath, &t)!
    }

效果：

Example 4 使用CAReplicatorLayer制作倒影:
思路：

1. 创建一个instanceCount为2的CAReplicatorLayer，其sourceLayer为contentLayer，copy为reflectLayer；
2. 设置其CAReplicatorLayer的instanceTransform使reflectLayer绕X轴翻转180°后，正好在contentLayer底部。
3. 添加一个CAGradientLayer使reflectLayer看起来像一个倒影的样子。
4. 可以将CAReplicatorLayer放在一个containerLayer中，CAGradientLayer作为containerLayer的子图层，正好覆盖reflectLayer，使用0.25alpha的白色到白色的渐变。
5. 也可以将GradientLayer作为containerLayer的mask，使用任意颜色到透明色的渐变。

    CGSize layerSize = CGSizeMake(200, 200);
    UIImage *image = [UIImage imageNamed:@"kobe.jpg"];
    // 倒影为原图的一半
    CGFloat totalHeigh = layerSize.height * 1.5;
    
    // containerLayer
    CALayer *container = [CALayer layer];
    container.bounds = CGRectMake(0, 0, layerSize.width, totalHeigh);
    container.position = self.view.center;
    [self.view.layer addSublayer:container];
    container.borderWidth =0.5;
    container.borderColor = [UIColor blackColor].CGColor;
    container.backgroundColor = [UIColor darkGrayColor].CGColor;
    
    // replicator
    CAReplicatorLayer *replicator = [CAReplicatorLayer layer];
    replicator.anchorPoint = CGPointZero;
    replicator.frame = CGRectMake(0, 0, layerSize.width, totalHeigh);
    replicator.backgroundColor = [UIColor lightGrayColor].CGColor;
    [container addSublayer:replicator];
    
    // config
    replicator.instanceCount = 2;
    CATransform3D transform = CATransform3DIdentity;
    transform = CATransform3DRotate(transform, M_PI, 1, 0, 0);
    
    // 旋转后坐标系也跟随旋转了180°，图层向下移动要减小y值
    transform = CATransform3DTranslate(transform, 0 , -layerSize.height * 2, 0);
    replicator.instanceTransform = transform;
    replicator.masksToBounds = YES;
    
    // a layer
    CALayer *contentLayer = [CALayer layer];
    contentLayer.anchorPoint = CGPointZero;
    contentLayer.frame = CGRectMake(0, 0, layerSize.width, layerSize.height);
    contentLayer.contentsScale = [UIScreen mainScreen].scale;
    contentLayer.shouldRasterize = YES;
    contentLayer.rasterizationScale = [UIScreen mainScreen].scale;
    contentLayer.contents = (id)image.CGImage;
    [replicator addSublayer:contentLayer];
    
    // create gradient
    CAGradientLayer *gradient = [CAGradientLayer layer];
    gradient.colors = @[
                        (id)[[UIColor whiteColor] colorWithAlphaComponent:0.25].CGColor,
                        (id)[UIColor whiteColor].CGColor
                        ];
    gradient.contentsScale = [UIScreen mainScreen].scale;
    gradient.frame = CGRectMake(0, layerSize.height, layerSize.width, layerSize.height * 0.5);
    [container addSublayer:gradient];
    
    /* mask 方式
    gradient.frame = container.bounds;
     gradient.colors = @[
     (id)[UIColor whiteColor].CGColor,
     (id)[[UIColor whiteColor] colorWithAlphaComponent:0.6].CGColor,
     (id)[UIColor clearColor].CGColor
     ];
     gradient.locations = @[
     @(200. / 300.),
     @(200.1 / 300.),
     @1
     ];
     container.mask = gradient;
     */

效果:

第三方：https://github.com/nicklockwood/ReflectionView