ios - NSLayoutManager: Calling setLocation(_:forStartOfGlyphRange:) disables kerning in the whole string? -

i created simple nslayoutmanager subclass allows set custom layout location defined substrings:

class positionablelayoutmanager: nslayoutmanager {     var xoffsetsperglyphrange = [(nsrange, cgpoint)]()      override func invalidatelayoutforcharacterrange(charrange: nsrange, actualcharacterrange actualcharrange: nsrangepointer) {         super.invalidatelayoutforcharacterrange(charrange, actualcharacterrange: actualcharrange)         (range, offset) in xoffsetsperglyphrange {             setlocation(offset, forstartofglyphrange: range)         }     } } 

now, can define custom location of character range this:

let glyphrange = layoutmanager.glyphrangeforcharacterrange(charrange, actualcharacterrange: nil) layoutmanager.xoffsetsperglyphrange.append((glyphrange, custompointlocation)) layoutmanager.invalidatelayoutforcharacterrange(nsrange(location: 0, length: textstorage.length), actualcharacterrange: nil) 

it works fine, problem glyph range repositioned in way laid out , drawn without kerning. here example:

in green box there text drawn using positionablelayoutmanager without kerning, in pink box there same text kering drawn using uilabel comparison.

how can same thing proper kerning?