Quartz 2D 画图（刷帧动画）

#import "KKView.h"

@interface KKView()
/** 图片的y值 */
@property (nonatomic, assign) CGFloat imgY;

@end

@implementation KKView

- (void)awakeFromNib{
      // 创建CADisplayLink, 默认每秒60次
      CADisplayLink *display = [CADisplayLink displayLinkWithTarget:self selector:@selector(updataImage)];
      // 将CADisplayLink加入到消息循环中
      [display addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
  
}
- (void)updataImage{
    // 这里会掉用drawRect方法
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect {

    CGContextRef ctx = UIGraphicsGetCurrentContext();
    
    CGContextClearRect(ctx, rect);
    
    CGImageRef img = [UIImage imageNamed:@"snow"].CGImage;
    
    CGRect imgRect;
    
    if (_imgY>rect.size.height) {
        _imgY = 0;
    }

    _imgY+=1;
    imgRect.origin.y = _imgY;
    imgRect.origin.x = 0;
    imgRect.size = CGSizeMake(50, 50);
    
    CGContextDrawImage(ctx, imgRect, img);
}

@end