旋转 锚点

ballLayer=[CALayer layer];

    ballLayer.bounds = CGRectMake(0, 0, 138,113);

    ballLayer.position = CGPointMake(self.view.frame.size.width/2,self.view.frame.size.height/2 );

   

    ballLayer.contents = (id)[UIImage imageNamed:@"closed@2x.png"].CGImage;

   

    ballLayer.anchorPoint = CGPointMake(0.5, 0);

[self.view.layer addSublayer:ballLayer];