Calculates the rect in which to draw the knob, then calls
drawKnob: Before calling this method, a
lockFocus message must be sent to the cell's control view.
When subclassing NSSliderCell, do not override this method. Override
Definition at line 165 of file ClockCell.m.
References drawKnob:, and knobRectFlipped:.
[self drawKnob: [self knobRectFlipped: [_control_view isFlipped]]];