1.CAShapeLayer
CAShapeLayer是一个通过矢量图形而不是bitmap来绘制的图层子类。你指定诸如颜色和线宽等属性，用CGPath来定义想要绘制的图形，最后CAShapeLayer就自动渲染出来了
相比Core Graphics之下，使用CAShapeLayer有以下一些优点：
渲染快速。CAShapeLayer使用了硬件加速，绘制同一图形会比用Core Graphics快很多。
高效使用内存。一个CAShapeLayer不需要像普通CALayer一样创建一个寄宿图形，所以无论有多大，都不会占用太多的内存。
不会被图层边界剪裁掉。一个CAShapeLayer可以在边界之外绘制。你的图层路径不会像在使用Core Graphics的普通CALayer一样被剪裁掉（如我们在第二章所见）。
不会出现像素化。当你给CAShapeLayer做3D变换时，它不像一个有寄宿图的普通图层一样变得像素化。
CAShapeLayer通过CGPath来表示形状。可以控制属性，lineWidth，lineCap，lineJoin，不过这些形状都只能是同一样的，一个layer只能设置一种。
创建带圆角和直角的图，创建圆角矩形其实就是人工绘制单独的直线和弧度，但是事实上UIBezierPath有自动绘制圆角矩形的构造方法
- (void)setCornerWithFlaot:(CGFloat)corner byRoundingCorners:(UIRectCorner)corners{
//define path
CGRect rect = self.bounds;
CGSize radii = CGSizeMake(corner, corner);
UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:rect
byRoundingCorners:corners
cornerRadii:radii];
//define layer
CAShapeLayer *shapeLayer = [CAShapeLayer layer];
shapeLayer.frame = self.bounds;
shapeLayer.path = path.CGPath;
self.layer.mask = shapeLayer;
}
2.CATransformLayer
CATransformLayerk可以将CALayer的构造的3D图链接起来放入同一3D空间中
3.CAGradientLayer
CAGradientLayer是用来生成两种或更多颜色平滑渐变的。但是CAGradientLayer的真正好处在于绘制使用了硬件加速。这些渐变色彩放在一个数组中，并赋给colors属性
- (void)viewDidLoad
{
[super viewDidLoad];
//create gradient layer and add it to our container view
CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = self.containerView.bounds;
[self.containerView.layer addSublayer:gradientLayer];
//set gradient colors
gradientLayer.colors = @[(__bridge id)[UIColor redColor].CGColor, (__bridge id)[UIColor blueColor].CGColor];
//set gradient start and end points
gradientLayer.startPoint = CGPointMake(0, 0);
gradientLayer.endPoint = CGPointMake(1, 1);
}
默认情况下，这些颜色在空间上均匀地被渲染，但是我们可以用locations属性来调整空间。locations属性是一个浮点数值的数组（以NSNumber包装）。这些浮点数定义了colors属性中每个不同颜色的位置，同样的，也是以单位坐标系进行标定。0.0代表着渐变的开始，1.0代表着结束。
//set locations
gradientLayer.locations = @[@0.0, @0.25, @0.5];
4.CAReplicatorLayer
CAReplicatorLayer的目的是为了高效生成许多相似的图层。
CAReplicatorLayer真正应用到实际程序上的场景比如：一个游戏中导弹的轨迹云，或者粒子爆炸（尽管iOS 5已经引入了CAEmitterLayer，它更适合创建任意的粒子效果）。除此之外，还有一个实际应用是：反射。
指定一个继承于UIView的ReflectionView，它会自动产生内容的反射效果
@implementation ReflectionView
+ (Class)layerClass
{
return [CAReplicatorLayer class];
}
- (void)setUp
{
//configure replicator
CAReplicatorLayer *layer = (CAReplicatorLayer *)self.layer;
layer.instanceCount = 2;
//move reflection instance below original and flip vertically
CATransform3D transform = CATransform3DIdentity;
CGFloat verticalOffset = self.bounds.size.height + 2;
transform = CATransform3DTranslate(transform, 0, verticalOffset, 0);
transform = CATransform3DScale(transform, 1, -1, 0);
layer.instanceTransform = transform;
//reduce alpha of reflection layer
layer.instanceAlphaOffset = -0.6;
}
- (id)initWithFrame:(CGRect)frame
{
//this is called when view is created in code
if ((self = [super initWithFrame:frame])) {
[self setUp];
}
return self;
}
- (void)awakeFromNib
{
//this is called when view is created from a nib
[self setUp];
}
@end
5.CATiledLayer
CATiledLayer很好地和UIScrollView集成在一起。除了设置图层和滑动视图边界以适配整个图片大小，我们真正要做的就是实现-drawLayer:inContext:方法，当需要载入新的小图时，CATiledLayer就会调用到这个方法。
#import "ViewController.h"
@interface ViewController ()
@property (nonatomic, weak) IBOutlet UIScrollView *scrollView;
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
//add the tiled layer
CATiledLayer *tileLayer = [CATiledLayer layer];
tileLayer.frame = CGRectMake(0, 0, 2048, 2048);
tileLayer.delegate = self;
tileLayer.contentsScale = [UIScreen mainScreen].scale;
[self.scrollView.layer addSublayer:tileLayer];
//configure the scroll view
self.scrollView.contentSize = tileLayer.frame.size;
//draw layer
[tileLayer setNeedsDisplay];
}
- (void)drawLayer:(CATiledLayer *)layer inContext:(CGContextRef)ctx
{
//determine tile coordinate
CGRect bounds = CGContextGetClipBoundingBox(ctx);
CGFloat scale = [UIScreen mainScreen].scale;
NSInteger x = floor(bounds.origin.x / layer.tileSize.width* scale);
NSInteger y = floor(bounds.origin.y / layer.tileSize.height* scale);
//load tile image
NSString *imageName = [NSString stringWithFormat: @"Snowman_%02i_%02i", x, y];
NSString *imagePath = [[NSBundle mainBundle] pathForResource:imageName ofType:@"jpg"];
UIImage *tileImage = [UIImage imageWithContentsOfFile:imagePath];
//draw tile
UIGraphicsPushContext(ctx);
[tileImage drawInRect:bounds];
UIGraphicsPopContext();
}
@end
CAEmitterLayer
苹果引入了一个新的CALayer子类叫做CAEmitterLayer。CAEmitterLayer是一个高性能的粒子引擎，被用来创建实时例子动画如：烟雾，火，雨等等这些效果。
AVPlayerLayer
AVPlayerLayer是用来在iOS上播放视频的。他是高级接口例如MPMoivePlayer的底层实现，提供了显示视频的底层控制。AVPlayerLayer的使用相当简单：你可以用+playerLayerWithPlayer:方法创建一个已经绑定了视频播放器的图层，或者你可以先创建一个图层，然后用player属性绑定一个AVPlayer实例。
- (void)viewDidLoad
{
[super viewDidLoad];
//get video URL
NSURL *URL = [[NSBundle mainBundle] URLForResource:@"Ship" withExtension:@"mp4"];
//create player and player layer
AVPlayer *player = [AVPlayer playerWithURL:URL];
AVPlayerLayer *playerLayer = [AVPlayerLayer playerLayerWithPlayer:player];
//set player layer frame and attach it to our view
playerLayer.frame = self.containerView.bounds;
[self.containerView.layer addSublayer:playerLayer];
//play the video
[player play];
}
因为AVPlayerLayer是CALayer的子类，它继承了父类的所有特性。我们并不会受限于要在一个矩形中播放视频；清单6.16演示了在3D，圆角，有色边框，蒙板，阴影等效果（见图6.17）.
- (void)viewDidLoad
{
...
//set player layer frame and attach it to our view
playerLayer.frame = self.containerView.bounds;
[self.containerView.layer addSublayer:playerLayer];
//transform layer
CATransform3D transform = CATransform3DIdentity;
transform.m34 = -1.0 / 500.0;
transform = CATransform3DRotate(transform, M_PI_4, 1, 1, 0);
playerLayer.transform = transform;
//add rounded corners and border
playerLayer.masksToBounds = YES;
playerLayer.cornerRadius = 20.0;
playerLayer.borderColor = [UIColor redColor].CGColor;
playerLayer.borderWidth = 5.0;
//play the video
[player play];
}
