iOS picture clipping

/**
 *  picture cropping
  cropping principle:
  First identify an area on the controller, and then put the picture that you want to crop to the area above which the image of the outside area does not display
 *
 *  @param rect
 */
-(void) DrawRect: (cgrect) rect{
    cgcontextref ref = Uigraphicsgetcurrentcontext ();
    
   //Draw a circle first
    cgcontextaddellipseinrect (ref, CGRectMake (100, 100, 100, 100));
    
   //Cut out the shape of the current context, and the later content can only be placed inside the shape
    cgcontextclip (ref);
    
   //Fill Circle
    cgcontextfillpath (ref);
    
   /Display picture
    UIImage *image = [UIImage imagenamed:@ "[email& Nbsp;protected] ";
    [Image Drawatpoint:cgpointmake (50, 50)];
}