mask layer

gistfile1.m

_maskLayer=[[CAGradientLayer layer]retain];
_maskLayer.frame=self.bounds;
_maskLayer.colors=@[(id)[UIColor colorWithRed:255/255.0f green:255.0f/255.0f blue:255/255.0f alpha:1.0f].CGColor,
             (id)[UIColor colorWithRed:255/255.0f green:255.0f/255.0f blue:255/255.0f alpha:0.0f].CGColor];
 _maskLayer.startPoint=CGPointMake(0.5, 0.3f);
_maskLayer.endPoint=CGPointMake(0.5f, 1.0f);
_maskLayer.locations=@[@0.0f,@1.0f];
self.layer.mask=_maskLayer;