摘要：
//CADisplayLink 和屏幕刷新频率相同 //开始下雪 - (void) beginShow{ //启动定时器,使得一直调用setNeedsDisplay从而调用- (void) drawRect:(CGRect )rect //不得手动调用- (void) drawRect:(CGRec 阅读全文
摘要：
@interface ViewController () @property (nonatomic,strong)UIImageView *topImageView; @property(nonatomic,strong)UIImageView *bottomImageView; @end @imp 阅读全文