整体描述

CAEmitter相关的是粒子动画，可以实现很多酷炫的效果

源码

/* CoreAnimation - CAEmitterCell.h

   Copyright (c) 2007-2016, Apple Inc.
   All rights reserved. */

#import <QuartzCore/CALayer.h>

NS_ASSUME_NONNULL_BEGIN

CA_CLASS_AVAILABLE (10.6, 5.0, 9.0, 2.0)
@interface CAEmitterCell : NSObject <NSCoding, CAMediaTiming>
{
@private
  void *_attr[2];
  void *_state;
  uint32_t _flags;
}

+ (instancetype)emitterCell;

/* Emitter cells implement the same property model as defined by CALayer.
 * See CALayer.h for more details. */

+ (nullable id)defaultValueForKey:(NSString *)key;
- (BOOL)shouldArchiveValueForKey:(NSString *)key;

/* The name of the cell. Used to construct key paths. Defaults to nil. */

@property(nullable, copy) NSString *name;

/* Controls whether or not cells from this emitter are rendered. */

@property(getter=isEnabled) BOOL enabled;

/* The number of emitted objects created every second. Default value is
 * zero. Animatable. */

@property float birthRate; // 每秒生成的粒子数量,默认值是1(支持隐式动画)

/* The lifetime of each emitted object in seconds, specified as a mean
 * value and a range about the mean. Both values default to zero.
 * Animatable. */

@property float lifetime; // 设置粒子的生存时间(支持隐式动画)默认是1.0
@property float lifetimeRange;

/* The orientation of the emission angle in radians, relative to the
 * natural orientation angle of the emission shape. Note that latitude
 * here is what is typically called colatitude, the zenith or phi, the
 * angle from the z-axis. Similarly longitude is the angle in the
 * xy-plane from the x-axis, often referred to as the azimuth or
 * theta. Both values default to zero, which translates to no change
 * relative to the emission shape's direction. Both values are
 * animatable. */

@property CGFloat emissionLatitude;
@property CGFloat emissionLongitude;

/* An angle (in radians) defining a cone around the emission angle.
 * Emitted objects are uniformly distributed across this cone. Defaults
 * to zero.  Animatable. */

@property CGFloat emissionRange;

/* The initial mean velocity of each emitted object, and its range. Both
 * values default to zero. Animatable. */

@property CGFloat velocity; // 设置粒子的移动速度(支持隐式动画)默认值是1.0
@property CGFloat velocityRange;

/* The acceleration vector applied to emitted objects. Defaults to
 * (0, 0, 0). Animatable. */

@property CGFloat xAcceleration;
@property CGFloat yAcceleration;
@property CGFloat zAcceleration;

/* The scale factor applied to each emitted object, defined as mean and
 * range about the mean. Scale defaults to one, range to zero.
 * Animatable. */

@property CGFloat scale; // 设置粒子发射器的生成粒子的初始缩放比例
@property CGFloat scaleRange;
@property CGFloat scaleSpeed;

/* The rotation speed applied to each emitted object, defined as mean
 * and range about the mean. Defaults to zero. Animatable. */

@property CGFloat spin; // 设置粒子的自旋速度,数值越大旋转越快
@property CGFloat spinRange;

/* The mean color of each emitted object, and the range from that mean
 * color. `color' defaults to opaque white, `colorRange' to (0, 0, 0,
 * 0). Animatable. */

@property(nullable) CGColorRef color;

@property float redRange;
@property float greenRange;
@property float blueRange;
@property float alphaRange;

/* The speed at which color components of emitted objects change over
 * their lifetime, defined as the rate of change per second. Defaults
 * to (0, 0, 0, 0). Animatable. */

@property float redSpeed;
@property float greenSpeed;
@property float blueSpeed;
@property float alphaSpeed;

/* The cell contents, typically a CGImageRef. Defaults to nil.
 * Animatable. */

@property(nullable, strong) id contents;

/* The sub-rectangle of the contents image that will be drawn. See
 * CALayer.h for more details. Defaults to the unit rectangle [0 0 1 1].
 * Animatable. */

@property CGRect contentsRect;

/* Defines the scale factor applied to the contents of the cell. See
 * CALayer.h for more details. */

@property CGFloat contentsScale;

/* The filter parameters used when rendering the `contents' image. See
 * CALayer.h for more details. */

@property(copy) NSString *minificationFilter;
@property(copy) NSString *magnificationFilter;
@property float minificationFilterBias;

/* An array containing the sub-cells of this cell, or nil (the default
 * value). When non-nil each particle emitted by the cell will act as
 * an emitter for each of the cell's sub-cells. The emission point is
 * the current particle position and the emission angle is relative to
 * the current direction of the particle. Animatable. */

@property(nullable, copy) NSArray<CAEmitterCell *> *emitterCells;

/* Inherited attributes similar to in layers. */

@property(nullable, copy) NSDictionary *style;

@end

NS_ASSUME_NONNULL_END