[self conrnerRadiusTest];
    
    //shadowPath
[self shadowPathTest];
    
    //mask
[self maskTest];

//拉伸過濾
[self filterTest];
    
    //alpha
[self alphaTest];

圓角conrnerRadius：默認情況下衣洁，這個曲率值只影響背景顏色而不影響背景圖片或是子圖層。不過攒读，如果把masksToBounds設置成YES的話绸贡，圖層里面的所有東西都會被截取。

- (void)conrnerRadiusTest {
    UIView *layerView1 = [[UIView alloc] init];
    layerView1.frame = CGRectMake(50.0f, 50.0f, 100.0f, 100.0f);
    layerView1.backgroundColor = [UIColor redColor];
    
    UIView *layerView2 = [[UIView alloc] init];
    layerView2.frame = CGRectMake(20.0f, 20.0f, 100.0f, 100.0f);
    layerView2.backgroundColor = [UIColor blueColor];
    [layerView2 addSubview:layerView1];
    
    UIView *shadowView = [[UIView alloc] init];
    shadowView.frame = CGRectMake(20.0f, 20.0f, 100.0f, 100.0f);
    shadowView.backgroundColor = [UIColor blueColor];
    [self.view addSubview:shadowView];
    [self.view addSubview:layerView2];


    //set the corner radius on our layers
    layerView1.layer.cornerRadius = 20.0f;
    layerView2.layer.cornerRadius = 10.0f;
    shadowView.layer.cornerRadius = 10.0f;
    
    //add a border to your layers
    layerView1.layer.borderWidth = 2.0f;
    layerView2.layer.borderWidth = 2.0f;
    
    //add a shadow to layerView1
    layerView2.layer.shadowOpacity = 0.5f;
    layerView2.layer.shadowOffset = CGSizeMake(0.0f, 5.0f);
    layerView2.layer.shadowRadius = 5.0f;
    
    //add same shadow to shadowView (not layerView2)
    shadowView.layer.shadowOpacity = 0.5f;
    shadowView.layer.shadowOffset = CGSizeMake(-10.0f, 10.0f);
    shadowView.layer.shadowRadius = 5.0f;
    
    //enable clipping on the second layer
    layerView2.layer.masksToBounds = YES;
}

圖層邊框

//borderWidth:以點為單位的定義邊框粗細的浮點數(shù)凛辣，默認為0.
//borderColor:定義了邊框的顏色抱既，默認為黑色。 CGColorRef

陰影

//shadowOpacity:是一個必須在0.0（不可見）和1.0（完全不透明）之間的浮點數(shù) 默認值0
//CALayer的另外三個屬性：shadowColor(CGColorRef)扁誓，shadowOffset(CGSize)默認值是 {0, -3}和shadowRadius屬性控制著陰影的模糊度防泵。

陰影裁剪

//圖層的陰影繼承自內(nèi)容的外形，而不是根據(jù)邊界和角半徑來確定
//一個只畫陰影的空的外圖層蝗敢，和一個用masksToBounds裁剪內(nèi)容的內(nèi)圖層

shadowPath屬性

//shadowPath是一個CGPathRef類型（一個指向CGPath的指針）捷泞。CGPath是一個Core Graphics對象，用來指定任意的一個矢量圖形寿谴。我們可以通過這個屬性單獨于圖層形狀之外指定陰影的形狀锁右。

- (void)shadowPathTest {
    UIView *layerView1 = [[UIView alloc] init];
    layerView1.frame = CGRectMake(50.0f, 50.0f, 100.0f, 100.0f);
    layerView1.backgroundColor = [UIColor redColor];
    
    UIView *layerView2 = [[UIView alloc] init];
    layerView2.frame = CGRectMake(200.0f, 200.0f, 100.0f, 100.0f);
    layerView2.backgroundColor = [UIColor blueColor];
    
    [self.view addSubview:layerView1];
    [self.view addSubview:layerView2];
    
    //enable layer shadows
    layerView1.layer.shadowOpacity = 0.5f;
    layerView2.layer.shadowOpacity = 0.5f;
    
    //create a squre shadow
    CGMutablePathRef squarePath = CGPathCreateMutable();
    CGPathAddRect(squarePath, NULL, layerView1.bounds);
    layerView1.layer.shadowPath = squarePath;
    CGPathRelease(squarePath);
    
    //create a cirular shadow
    CGMutablePathRef circlePath = CGPathCreateMutable();
    CGPathAddEllipseInRect(circlePath, NULL, layerView2.bounds);
    layerView2.layer.shadowPath = circlePath;
    CGPathRelease(circlePath);
}

圖層蒙板

//mask:CALayer類型 mask圖層定義了父圖層的部分可見區(qū)域

- (void)maskTest {
    UIImageView *mealView = [[UIImageView alloc] init];
    mealView.frame = CGRectMake(50.0f, 50.0f, 200.0f, 200.0f);
    mealView.image = [UIImage imageNamed:@"Meal"];
    [self.view addSubview:mealView];
    
    //create mask layer
    CALayer *maskLayer = [CALayer layer];
    maskLayer.frame = CGRectMake(10.0f, 10.0f, 60.0f, 60.0f);
    UIImage *maskImage = [UIImage imageNamed:@"Meal"];
    maskLayer.contents = (__bridge id)maskImage.CGImage;

    //apply mask to image layer
    mealView.layer.mask = maskLayer;
}

拉伸過濾

//minificationFilter:縮小圖片
//magnificationFilter:放大圖片
/*
CALayer為此提供了三種拉伸過濾方法，他們是：
kCAFilterLinear: 默認 雙線性濾波算法
kCAFilterNearest: 三線性濾波算法
kCAFilterTrilinear:最近過濾 就是取樣最近的單像素點而不管其他的顏色
*/

- (void)filterTest {
    UIImage *digits = [UIImage imageNamed:@"Meal"];
    
    //set up digit views
    for (int k = 0; k < 6; k++) {
        UIView *view = [[UIView alloc] init];
        view.frame = CGRectMake(0.0, 110 * k, 100.0f, 100.0f);
        view.layer.contents = (__bridge id)digits.CGImage;
        view.layer.contentsRect = CGRectMake(0.0, 0.0f, 0.1f, 1.0f);
        view.layer.contentsGravity = kCAGravityResizeAspect;
        //filter
        view.layer.magnificationFilter = kCAFilterNearest;
        [self.view addSubview:view];
    }
    
    timerDigit = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(tickDigit) userInfo:nil repeats:YES];
    
    //set initial clock time
    [self tickDigit];
}

- (void)setDigit:(NSInteger)digit forView:(UIView *)view {
    //adjust contentsRect to select correct digit
    view.layer.contentsRect = CGRectMake(digit * 0.1, 0, 0.1, 1.0);
}

- (void)tickDigit {
    //convert time to hours, minutes and seconds
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSUInteger units = NSCalendarUnitHour| NSCalendarUnitMinute | NSCalendarUnitSecond;
    NSDateComponents *components = [calendar components:units fromDate:[NSDate date]];
    
    //set hours
    [self setDigit:components.hour / 10 forView:digitViews[0]];
    [self setDigit:components.hour % 10 forView:digitViews[1]];
    
    //set minutes
    [self setDigit:components.minute / 10 forView:digitViews[2]];
    [self setDigit:components.minute % 10 forView:digitViews[3]];
    
    //set second
    [self setDigit:components.second / 10 forView:digitViews[4]];
    [self setDigit:components.second % 10 forView:digitViews[5]];
}

組透明

//UIView有一個叫做alpha的屬性來確定視圖的透明度讶泰。CALayer有一個等同的屬性叫做opacity咏瑟，這兩個屬性都是影響子層級的

//設置了一個圖層的透明度，它包含的整個圖層樹像一個整體一樣的透明效果
//1種Info.plist文件中的UIViewGroupOpacity為YES來達到峻厚，但是這個設置會影響到這個應用响蕴，整個app可能會受到不良影響。
//2種設置CALayer的一個叫做shouldRasterize屬性
//為了啟用shouldRasterize屬性惠桃，我們設置了圖層的rasterizationScale屬性浦夷。默認情況下，所有圖層拉伸都是1.0辜王， 所以如果你使用了shouldRasterize屬性劈狐，你就要確保你設置了rasterizationScale屬性去匹配屏幕，以防止出現(xiàn)Retina屏幕像素化的問題呐馆。
//shouldRasterize和UIViewGroupOpacity一起的時候肥缔，性能問題就出現(xiàn)了

- (UIButton *)customButton {
    //creat button
    CGRect frame = CGRectMake(0, 0, 150, 150);
    UIButton *button = [[UIButton alloc] initWithFrame:frame];
    button.backgroundColor = [UIColor redColor];
    button.layer.cornerRadius = 10;
    
    //add label
    frame = CGRectMake(20, 10, 110, 30);
    UILabel *label = [[UILabel alloc] initWithFrame:frame];
    label.text = @"Hello Word";
    label.textAlignment = NSTextAlignmentCenter;
    [button addSubview:label];
    return button;
}

- (void)alphaTest {
    //create opaque button
    UIButton *button1 = [self customButton];
    button1.center = CGPointMake(50, 150);
    [self.view addSubview:button1];
    
    //create translucent button
    UIButton *button2 = [self customButton];
    button2.center = CGPointMake(250, 150);
    button2.alpha = 0.5;
    [self.view addSubview:button2];
    
    //enable rasterization for the translucent button
    button2.layer.shouldRasterize = YES;
    button2.layer.rasterizationScale = [UIScreen mainScreen].scale;
}