IOS Core Animation Advanced Techniques

 #import "ViewController.h"
 #import

 @interface ViewController ()

 @property (nonatomic, weak) IBOutlet UIView *layerView1;
 @property (nonatomic, weak) IBOutlet UIView *layerView2;

 @end

 @implementation ViewController

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //set the corner radius on our layers
     self.layerView1.layer.cornerRadius = 20.0f;
     self.layerView2.layer.cornerRadius = 20.0f;

     //enable clipping on the second layer
     self.layerView2.layer.masksToBounds = YES;
 }

 @end

稍微修改一下

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //set the corner radius on our layers
     self.layerView1.layer.cornerRadius = 20.0f;
     self.layerView2.layer.cornerRadius = 20.0f;

     self.layerView1.clipsToBounds = YES;

     //enable clipping on the second layer
     self.layerView2.layer.masksToBounds = YES;
 }

前面讲过了，UIView的clipsToBounds的函数等同于masksToBounds


Layer Borders

例子4.2 borderWidth

 @interface ViewController ()

 @property (nonatomic, weak) IBOutlet UIView *layerView1;
 @property (nonatomic, weak) IBOutlet UIView *layerView2;

 @end

 @implementation ViewController

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //set the corner radius on our layers
     self.layerView1.layer.cornerRadius = 20.0f;
     self.layerView2.layer.cornerRadius = 20.0f;

     //add a border to our layers
     self.layerView1.layer.borderWidth = 5.0f;
     self.layerView2.layer.borderWidth = 5.0f;

     //enable clipping on the second layer
     self.layerView2.layer.masksToBounds = YES;
 }

 @end

修改代码 borderColor

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //set the corner radius on our layers
     self.layerView1.layer.cornerRadius = 20.0f;
     self.layerView2.layer.cornerRadius = 20.0f;

     //add a border to our layers
     self.layerView1.layer.borderWidth = 5.0f;
     self.layerView1.layer.borderColor = [UIColor brownColor].CGColor;
     self.layerView2.layer.borderWidth = 5.0f;

     //enable clipping on the second layer
     self.layerView2.layer.masksToBounds = YES;
 }

再做个试验，修改代码

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //set the corner radius on our layers
     //self.layerView1.layer.cornerRadius = 20.0f;
     self.layerView2.layer.cornerRadius = 20.0f;

     //add a border to our layers
     self.layerView1.layer.borderWidth = 5.0f;
     self.layerView1.layer.borderColor = [UIColor brownColor].CGColor;
     self.layerView2.layer.borderWidth = 5.0f;

     //enable clipping on the second layer
     self.layerView2.layer.masksToBounds = YES;
 }

没有看到红色

再修改

看结果

验证borderWidth是往内部画的，和使用CGContextStrokeEllipseInRect画圆时的方式不同

Drop Shadows & Shadow Clipping

先修改例子2.2

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //load an image
     UIImage *image = [UIImage imageNamed:@"Snowman.png"];

     self.layerView.backgroundColor = [UIColor clearColor];

     //add it directly to our view's layer
     self.layerView.layer.contents = (__bridge id)image.CGImage;

     //center the image
     self.layerView.layer.contentsGravity = kCAGravityCenter;

     //set the contentsScale to match screen
     self.layerView.layer.contentsScale = image.scale;

     self.layerView.layer.shadowOpacity = 0.3;
     self.layerView.layer.shadowOffset = CGSizeMake(10, 20);

     //clip the snowman to fit his bounds
     //self.layerView.layer.masksToBounds = YES;
 }

继续

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //load an image
     UIImage *image = [UIImage imageNamed:@"Snowman.png"];

     //self.layerView.backgroundColor = [UIColor clearColor];

     //add it directly to our view's layer
     self.layerView.layer.contents = (__bridge id)image.CGImage;

     //center the image
     self.layerView.layer.contentsGravity = kCAGravityCenter;

     //set the contentsScale to match screen
     self.layerView.layer.contentsScale = image.scale;

     self.layerView.layer.shadowOpacity = 0.3;
     self.layerView.layer.shadowOffset = CGSizeMake(10, 20);

     //clip the snowman to fit his bounds
     //self.layerView.layer.masksToBounds = YES;
 }

再改

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //load an image
     UIImage *image = [UIImage imageNamed:@"Snowman.png"];

     self.layerView.backgroundColor = [UIColor clearColor];

     //add it directly to our view's layer
     self.layerView.layer.contents = (__bridge id)image.CGImage;

     //center the image
     self.layerView.layer.contentsGravity = kCAGravityCenter;

     //set the contentsScale to match screen
     self.layerView.layer.contentsScale = image.scale;

     self.layerView.layer.shadowOpacity = 0.3;
     self.layerView.layer.shadowOffset = CGSizeMake(10, 20);

     //clip the snowman to fit his bounds
     self.layerView.layer.masksToBounds = YES;
 }

再改

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //load an image
     UIImage *image = [UIImage imageNamed:@"Snowman.png"];

     //self.layerView.backgroundColor = [UIColor clearColor];

     //add it directly to our view's layer
     self.layerView.layer.contents = (__bridge id)image.CGImage;

     //center the image
     self.layerView.layer.contentsGravity = kCAGravityCenter;

     //set the contentsScale to match screen
     self.layerView.layer.contentsScale = image.scale;

     self.layerView.layer.shadowOpacity = 0.3;
     self.layerView.layer.shadowOffset = CGSizeMake(10, 20);

     //clip the snowman to fit his bounds
     self.layerView.layer.masksToBounds = YES;
 }

shadow是根据layer实际显示的内容绘制的

再看看例子4.3去体会一下

源码在这里下载：http://www.informit.com/title/9780133440751

The shadowPath Property

例子4.4

 @interface ViewController ()

 @property (nonatomic, weak) IBOutlet UIView *layerView1;
 @property (nonatomic, weak) IBOutlet UIView *layerView2;

 @end

 @implementation ViewController

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //enable layer shadows
     self.layerView1.layer.shadowOpacity = 0.5f;
     self.layerView2.layer.shadowOpacity = 0.5f;

     //create a square shadow
     CGMutablePathRef squarePath = CGPathCreateMutable();
     CGPathAddRect(squarePath, NULL, self.layerView1.bounds);
     self.layerView1.layer.shadowPath = squarePath;
     CGPathRelease(squarePath);

     //create a circular shadow
     CGMutablePathRef circlePath = CGPathCreateMutable();
     CGPathAddEllipseInRect(circlePath, NULL, self.layerView2.bounds);
     self.layerView2.layer.shadowPath = circlePath;
     CGPathRelease(circlePath);
 }

Layer Masking

例子4.5

 @interface ViewController ()

 @property (nonatomic, weak) IBOutlet UIImageView *imageView;

 @end

 @implementation ViewController

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //create mask layer
     CALayer *maskLayer = [CALayer layer];
     maskLayer.frame = self.imageView.bounds;
     UIImage *maskImage = [UIImage imageNamed:@"Cone.png"];
     maskLayer.contents = (__bridge id)maskImage.CGImage;

     //apply mask to image layer
     self.imageView.layer.mask = maskLayer;
 }

 @end

Scaling Filters

minificationFilter和magnificationFilter属性

这两个属性主要是设置layer的‘contents’数据缩放拉伸时的描绘方式，minificationFilter用于缩小，magnificationFilter用于放大

默认值都是kCAFilterLinear即‘linear’

有3中设置：kCAFilterLinear，kCAFilterNearest，kCAFilterTrilinear

kCAFilterLinear：默认值，缩放平滑，但容易产生模糊效果

kCAFilterTrilinear：基本和kCAFilterLinear相同

kCAFilterNearest：速度快不会产生模糊，但会降低质量并像素化图像

例子4.6，放大图像，设置magnificationFilter

原图   

 @interface ViewController ()

 @property (nonatomic, strong) IBOutletCollection(UIView) NSArray *digitViews;
 @property (nonatomic, weak) NSTimer *timer;

 @end

 @implementation ViewController

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //get spritesheet image
     UIImage *digits = [UIImage imageNamed:@"Digits.png"];

     //set up digit views
     for (UIView *view in self.digitViews)
     {
         //set contents
         view.layer.contents = (__bridge  id)digits.CGImage;
         view.layer.contentsRect = CGRectMake(0, 0, 0.1, 1.0);
         view.layer.contentsGravity = kCAGravityResizeAspect;

         //use nearest-neighbor scaling
         view.layer.magnificationFilter = kCAFilterNearest;
     }

     //start timer
     self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0
                                                   target:self
                                                 selector:@selector(tick)
                                                 userInfo:nil
                                                  repeats:YES];
     //set initial clock time
     [self tick];
 }

 - (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)tick
 {
     //convert time to hours, minutes and seconds
     NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
     NSUInteger units = NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
     NSDateComponents *components = [calendar components:units fromDate:[NSDate date]];

     //set hours
     [self setDigit:components.hour / 10 forView:self.digitViews[0]];
     [self setDigit:components.hour % 10 forView:self.digitViews[1]];

     //set minutes
     [self setDigit:components.minute / 10 forView:self.digitViews[2]];
     [self setDigit:components.minute % 10 forView:self.digitViews[3]];

     //set seconds
     [self setDigit:components.second / 10 forView:self.digitViews[4]];
     [self setDigit:components.second % 10 forView:self.digitViews[5]];
 }

 @end

kCAFilterNearest的效果

注释掉

 //view.layer.magnificationFilter = kCAFilterNearest;

使用用默认kCAFilterLinear效果

明显模糊了

Group Opacity

先看例子4.7：

 @interface ViewController ()

 @property (nonatomic, weak) IBOutlet UIView *containerView;

 @end

 @implementation ViewController

 - (UIButton *)customButton
 {
     //create button
     CGRect frame = CGRectMake(0, 0, 150, 50);
     UIButton *button = [[UIButton alloc] initWithFrame:frame];
     button.backgroundColor = [UIColor whiteColor];
     button.layer.cornerRadius = 10;

     //add label
     frame = CGRectMake(20, 10, 110, 30);
     UILabel *label = [[UILabel alloc] initWithFrame:frame];
     label.text = @"Hello World";
     //label.backgroundColor = [UIColor clearColor];
     label.textAlignment = NSTextAlignmentCenter;
     [button addSubview:label];

     return button;
 }

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //create opaque button
     UIButton *button1 = [self customButton];
     button1.center = CGPointMake(50, 150);
     [self.containerView addSubview:button1];

     //create translucent button
     UIButton *button2 = [self customButton];
     button2.center = CGPointMake(250, 150);
     button2.alpha = 0.5;
     [self.containerView addSubview:button2];

     //enable rasterization for the translucent button
     //button2.layer.shouldRasterize = YES;
     //button2.layer.rasterizationScale = [UIScreen mainScreen].scale;
 }

 @end

button的背景和其subView label的背景同为白色，

左边的button是不透明的，右边用同样方式创建的button透明度为50%，发现右边的label透明度不同于button

其实很容易发现原因，将button透明度设为50%后，button显示50%自己的颜色和其后面50%的颜色，label在

button上面，label也是50%显示择机的颜色，但后面有已经50%透明的button，还要再显示它的50%，即原

button的25%，重合后为75%，即出现上图效果。

有两种解决方法：

1.在工程的Info.plist文件中，添加UIViewGroupOpacity并设为YES

2.设置layer属性shouldRasterize，设为YES可在设置opacity属性时将layer及其sublayer叠加为一张图像

修改代码，

 - (void)viewDidLoad
 {
     [super viewDidLoad];

     //create opaque button
     UIButton *button1 = [self customButton];
     button1.center = CGPointMake(50, 150);
     [self.containerView addSubview:button1];

     //create translucent button
     UIButton *button2 = [self customButton];
     button2.center = CGPointMake(250, 150);
     button2.alpha = 0.5;
     [self.containerView addSubview:button2];

     //enable rasterization for the translucent button
     button2.layer.shouldRasterize = YES;
     button2.layer.rasterizationScale = [UIScreen mainScreen].scale;
 }