contens 属性可以给layer赋值CGImage
contentsGravity属性类似contentModel：kCAGravityResizeAspect
contentsScale属性用来设置渲染倍数 
contentsRect用来显示contents中指定区域，适用于雪碧图的展示

// 裁剪并显示雪碧图，不用从内存中读多张图片，4张图片在一张雪碧图中
- (void)addSpriteImage:(UIImage *)img withContentRect:(CGRect)rect toLayer:(CALayer *)layer
{
    layer.contents = (__bridge id)(img.CGImage);
    layer.contentsGravity = kCAGravityResizeAspect;
    layer.contentsRect = rect;
}

- (void)layoutSublayersOfLayer:(CALayer *)layer;

CGAffineTransformRotate(CGAffineTransform t, CGFloat angle)     
CGAffineTransformScale(CGAffineTransform t, CGFloat sx, CGFloat sy)      
CGAffineTransformTranslate(CGAffineTransform t, CGFloat tx, CGFloat ty)

CATransform3DMakeRotation(CGFloat angle, CGFloat x, CGFloat y, CGFloat z)
CATransform3DMakeScale(CGFloat sx, CGFloat sy, CGFloat sz)
CATransform3DMakeTranslation(Gloat tx, CGFloat ty, CGFloat tz)

 CATransform3D transform = CATransform3DIdentity;
    transform.m34 = - 1.0 / 500.0;
    transform = CATransform3DRotate(transform, M_PI_4, 0, 1, 0);
    self.layerView.layer.transform = transform;

CATransform3D perspective = CATransform3DIdentity;
    perspective.m34 = -1.0 / 500.0;
    
    // 都旋转一个角度,看到侧面
    perspective = CATransform3DRotate(perspective, -M_PI_4, 1, 0, 0);
    perspective = CATransform3DRotate(perspective, -M_PI_4, 0, 1, 0);
    
    self.view.layer.sublayerTransform = perspective;
    //add cube face 1
    CATransform3D transform = CATransform3DMakeTranslation(0, 0, 100);
    [self addFace:0 withTransform:transform];
    //add cube face 2
    transform = CATransform3DMakeTranslation(100, 0, 0);
    transform = CATransform3DRotate(transform, M_PI_2, 0, 1, 0);
    [self addFace:1 withTransform:transform];
    //add cube face 3
    transform = CATransform3DMakeTranslation(0, -100, 0);
    transform = CATransform3DRotate(transform, M_PI_2, 1, 0, 0);
    [self addFace:2 withTransform:transform];
    //add cube face 4
    transform = CATransform3DMakeTranslation(0, 100, 0);
    transform = CATransform3DRotate(transform, -M_PI_2, 1, 0, 0);
    [self addFace:3 withTransform:transform];
    //add cube face 5
    transform = CATransform3DMakeTranslation(-100, 0, 0);
    transform = CATransform3DRotate(transform, -M_PI_2, 0, 1, 0);
    [self addFace:4 withTransform:transform];
    //add cube face 6
    transform = CATransform3DMakeTranslation(0, 0, -100);
    transform = CATransform3DRotate(transform, M_PI, 0, 1, 0);
    [self addFace:5 withTransform:transform];
    

CGRect rect = CGRectMake(50, 50, 100, 100);
    CGSize radii = CGSizeMake(20, 20);
    UIRectCorner corners = UIRectCornerTopRight | UIRectCornerBottomLeft | UIRectCornerTopLeft;
    UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:corners cornerRadii:radii];
    
CAShapeLayer *layer = [CAShapeLayer layer];
........ // 设置宽度颜色等
layer.path = path.CGPath;

- (CALayer *)cubeWithTransform:(CATransform3D)transform
{
  //create cube layer
  CATransformLayer *cube = [CATransformLayer layer];

  //add cube face 1
  CATransform3D ct = CATransform3DMakeTranslation(0, 0, 50);
  [cube addSublayer:[self faceWithTransform:ct]];

// .......

  //add cube face 6
  ct = CATransform3DMakeTranslation(0, 0, -50);
  ct = CATransform3DRotate(ct, M_PI, 0, 1, 0);
  [cube addSublayer:[self faceWithTransform:ct]];

  //center the cube layer within the container
  CGSize containerSize = self.containerView.bounds.size;
  cube.position = CGPointMake(containerSize.width / 2.0, containerSize.height / 2.0);

  //apply the transform and return
  cube.transform = transform;
  return cube;
}

- (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 yellowColor].CGColor, (__bridge id)[UIColor greenColor].CGColor];

	//set locations
	gradientLayer.locations = @[@0.0, @0.25, @0.5];

	//set gradient start and end points
	gradientLayer.startPoint = CGPointMake(0, 0);
	gradientLayer.endPoint = CGPointMake(1, 1);
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    //create a replicator layer and add it to our view
    CAReplicatorLayer *replicator = [CAReplicatorLayer layer];
    replicator.frame = self.containerView.bounds;
    [self.containerView.layer addSublayer:replicator];

    //configure the replicator
    replicator.instanceCount = 10;

    //apply a transform for each instance
    CATransform3D transform = CATransform3DIdentity;
    transform = CATransform3DTranslate(transform, 0, 200, 0);
    transform = CATransform3DRotate(transform, M_PI / 5.0, 0, 0, 1);
    transform = CATransform3DTranslate(transform, 0, -200, 0);
    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(100.0f, 100.0f, 100.0f, 100.0f);
    layer.backgroundColor = [UIColor whiteColor].CGColor;
    [replicator addSublayer:layer];
}

 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;

- (void)drawLayer:(CATiledLayer *)layer inContext:(CGContextRef)ctx
{
    //determine tile coordinate
    CGRect bounds = CGContextGetClipBoundingBox(ctx);
    NSInteger x = floor(bounds.origin.x / layer.tileSize.width);
    NSInteger y = floor(bounds.origin.y / layer.tileSize.height);

    //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();
}

   CAEmitterLayer *emitter = [CAEmitterLayer layer];
    emitter.frame = self.view.bounds;
    [self.view.layer addSublayer:emitter];

    //configure emitter
    emitter.renderMode = kCAEmitterLayerAdditive;
    emitter.emitterPosition = CGPointMake(emitter.frame.size.width / 2.0, emitter.frame.size.height / 2.0);

    //create a particle template
    CAEmitterCell *cell = [[CAEmitterCell alloc] init];
    cell.contents = (__bridge id)[UIImage imageNamed:@"Spark.png"].CGImage;
    cell.birthRate = 150;
    cell.lifetime = 5.0;
    cell.color = [UIColor colorWithRed:1 green:0.5 blue:0.1 alpha:1.0].CGColor;
    cell.alphaSpeed = -0.4;
    cell.velocity = 50;
    cell.velocityRange = 50;
    cell.emissionRange = M_PI * 2.0;

    //add particle template to emitter
    emitter.emitterCells = @[cell];

#import "ViewController.h"
#import <QuartzCore/QuartzCore.h>
#import <GLKit/GLKit.h>

@interface ViewController ()

@property (nonatomic, weak) IBOutlet UIView *glView;
@property (nonatomic, strong) EAGLContext *glContext;
@property (nonatomic, strong) CAEAGLLayer *glLayer;
@property (nonatomic, assign) GLuint framebuffer;
@property (nonatomic, assign) GLuint colorRenderbuffer;
@property (nonatomic, assign) GLint framebufferWidth;
@property (nonatomic, assign) GLint framebufferHeight;
@property (nonatomic, strong) GLKBaseEffect *effect;

@end

@implementation ViewController

- (void)setUpBuffers
{
    //set up frame buffer
    glGenFramebuffers(1, &_framebuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer);

    //set up color render buffer
    glGenRenderbuffers(1, &_colorRenderbuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, _colorRenderbuffer);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, _colorRenderbuffer);
    [self.glContext renderbufferStorage:GL_RENDERBUFFER fromDrawable:self.glLayer];
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &_framebufferWidth);
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &_framebufferHeight);

    //check success
    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
        NSLog(@"Failed to make complete framebuffer object: %i", glCheckFramebufferStatus(GL_FRAMEBUFFER));
    }
}

- (void)tearDownBuffers
{
    if (_framebuffer) {
        //delete framebuffer
        glDeleteFramebuffers(1, &_framebuffer);
        _framebuffer = 0;
    }

    if (_colorRenderbuffer) {
        //delete color render buffer
        glDeleteRenderbuffers(1, &_colorRenderbuffer);
        _colorRenderbuffer = 0;
    }
}

- (void)drawFrame {
    //bind framebuffer & set viewport
    glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer);
    glViewport(0, 0, _framebufferWidth, _framebufferHeight);

    //bind shader program
    [self.effect prepareToDraw];

    //clear the screen
    glClear(GL_COLOR_BUFFER_BIT); glClearColor(0.0, 0.0, 0.0, 1.0);

    //set up vertices
    GLfloat vertices[] = {
        -0.5f, -0.5f, -1.0f, 0.0f, 0.5f, -1.0f, 0.5f, -0.5f, -1.0f,
    };

    //set up colors
    GLfloat colors[] = {
        0.0f, 0.0f, 1.0f, 1.0f, 0.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f,
    };

    //draw triangle
    glEnableVertexAttribArray(GLKVertexAttribPosition);
    glEnableVertexAttribArray(GLKVertexAttribColor);
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 0, vertices);
    glVertexAttribPointer(GLKVertexAttribColor,4, GL_FLOAT, GL_FALSE, 0, colors);
    glDrawArrays(GL_TRIANGLES, 0, 3);

    //present render buffer
    glBindRenderbuffer(GL_RENDERBUFFER, _colorRenderbuffer);
    [self.glContext presentRenderbuffer:GL_RENDERBUFFER];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    //set up context
    self.glContext = [[EAGLContext alloc] initWithAPI: kEAGLRenderingAPIOpenGLES2];
    [EAGLContext setCurrentContext:self.glContext];

    //set up layer
    self.glLayer = [CAEAGLLayer layer];
    self.glLayer.frame = self.glView.bounds;
    [self.glView.layer addSublayer:self.glLayer];
    self.glLayer.drawableProperties = @{kEAGLDrawablePropertyRetainedBacking:@NO, kEAGLDrawablePropertyColorFormat: kEAGLColorFormatRGBA8};

    //set up base effect
    self.effect = [[GLKBaseEffect alloc] init];

    //set up buffers
    [self setUpBuffers];

    //draw frame
    [self drawFrame];
}

- (void)viewDidUnload
{
    [self tearDownBuffers];
    [super viewDidUnload];
}

- (void)dealloc
{
    [self tearDownBuffers];
    [EAGLContext setCurrentContext:nil];
}
@end

由AVFoundation框架提供用于播放视频的图层。 因为本身是CALayer的子类，所以也支持layer该有的效果，例如边框，圆角，蒙版，阴影等。

CATransition *transition = [CATransition animation];
transition.type = kCATransitionPush;
transition.subtype = kCATransitionFromLeft;
self.colorLayer.actions = @{@"backgroundColor": transition};

显式动画相对于隐式动画，是用户自己主动创建的一种动画类型，与隐式动画做的关于属性动画不同。 ### 属性动画
作用于图层的某个单一属性，并指定了它的一个或一连串目标值，分为基础动画和关键帧动画，即CABasicAnimation和CAKeyframeAnimation

最简单的形式就是从一个值改变到另一个值，这也是CABasicAnimation最主要的功能。提供了fromValue, toValue, byValue三个属性。fromValue代表了动画开始之前属性的值，toValue代表了动画结束之后的值，byValue代表了动画执行过程中改变的相对值。

 CABasicAnimation *animation = [CABasicAnimation animation];
    animation.keyPath = @"backgroundColor";
    animation.toValue = (__bridge id)color.CGColor;
    [self.colorLayer addAnimation:animation forKey:nil];

CABasicAnimation揭示了大多数隐式动画背后依赖的机制，这的确很有趣，但是显式地给图层添加CABasicAnimation相较于隐式动画而言，只能说费力不讨好。 CAKeyframeAnimation是另一种UIKit没有暴露出来但功能强大的类。不光能设置单一值，还能设置一串值。

CAKeyframeAnimation *animation = [CAKeyframeAnimation animation];
    animation.keyPath = @"backgroundColor";
    animation.duration = 2.0;
    animation.values = @[
                         (__bridge id)[UIColor blueColor].CGColor,
                         (__bridge id)[UIColor redColor].CGColor,
                         (__bridge id)[UIColor greenColor].CGColor,
                         (__bridge id)[UIColor blueColor].CGColor ];
    [self.colorLayer addAnimation:animation forKey:nil];

CAKeyframeAnimation *animation = [CAKeyframeAnimation animation];
    animation.keyPath = @"position";
    animation.duration = 4.0;
    animation.path = bezierPath.CGPath;
    [shipLayer addAnimation:animation forKey:nil];

前面的属性动画都针对真实属性，例如backgroundColor, position等。如果想对一个属性的路径，或不是真实属性做动画，就是虚拟属性。

CABasicAnimation *animation = [CABasicAnimation animation];
animation.keyPath = @"transform";
animation.toValue = [NSValue valueWithCATransform3D: CATransform3DMakeRotation(M_PI, 0, 0, 1)];

CABasicAnimation *animation = [CABasicAnimation animation];
animation.keyPath = @"transform.rotation";
animation.byValue = @(M_PI * 2);

过渡并不像属性动画那样平滑地在两个值之间做动画，而是影响到整个图层的变化。过渡动画首先展示之前的图层外观，然后通过一个交换过渡到新的外观。

过渡是一种对那些不太好做平滑动画属性的强大工具，但是CATransition的提供的动画类型太少了。 UIView +transitionFromView:toView:duration:options:completion: 提供的过渡选项却很多 - UIViewAnimationOptionTransitionFlipFromLeft  - UIViewAnimationOptionTransitionFlipFromRight - UIViewAnimationOptionTransitionCurlUp  - UIViewAnimationOptionTransitionCurlDown - UIViewAnimationOptionTransitionCrossDissolve  - UIViewAnimationOptionTransitionFlipFromTop  - UIViewAnimationOptionTransitionFlipFromBottom

kCAFillModeForwards
kCAFillModeBackwards
kCAFillModeBoth
kCAFillModeRemoved

为了让动画显得更自然，而不是很机械，需要使用时间函数控制动画速率

CAAnimation的timingFunciont属性接收一个CAMediaTimingFunction对象。 包含以下类型 - kCAMediaTimingFunctionLinear  - kCAMediaTimingFunctionEaseIn  - kCAMediaTimingFunctionEaseOut  - kCAMediaTimingFunctionEaseInEaseOut - kCAMediaTimingFunctionDefault

UIView的动画也支持时间函数，参考CAAnimation的函数 - UIViewAnimationOptionCurveEaseInOut  - UIViewAnimationOptionCurveEaseIn  - UIViewAnimationOptionCurveEaseOut  - UIViewAnimationOptionCurveLinear

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    //get the current point
    CGPoint point = [[touches anyObject] locationInView:self];

    //add a new line segment to our path
    [self.path addLineToPoint:point];

    //redraw the view
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect
{
    //draw path
    [[UIColor clearColor] setFill];
    [[UIColor redColor] setStroke];
    [self.path stroke];
}

+ (Class)layerClass
{
    //this makes our view create a CAShapeLayer
    //instead of a CALayer for its backing layer
    return [CAShapeLayer class];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    //get the current point
    CGPoint point = [[touches anyObject] locationInView:self];

    //add a new line segment to our path
    [self.path addLineToPoint:point];

    //update the layer with a copy of the path
    ((CAShapeLayer *)self.layer).path = self.path.CGPath;
}

NSInteger index = indexPath.row;
NSURL *imageURL = [NSURL fileURLWithPath:self.imagePaths[index]];
NSDictionary *options = @{(__bridge id)kCGImageSourceShouldCache: @YES}; 
CGImageSourceRef source = CGImageSourceCreateWithURL((__bridge CFURLRef)imageURL, NULL);
CGImageRef imageRef = CGImageSourceCreateImageAtIndex(source, 0,(__bridge CFDictionaryRef)options);
UIImage *image = [UIImage imageWithCGImage:imageRef]; 
CGImageRelease(imageRef);
CFRelease(source);