question: private void updateSliderState ( int touchX , int touchY ) { int distanceX = touchX - mCircleCenterX ; int distanceY = mCircleCenterY - touchY ; double c = Math . sqrt ( Math . pow ( distanceX , 2 ) + Math . pow ( distanceY , 2 ) ) ; mAngle = Math . acos ( distanceX / c ) ; if ( distanceY < 0 ) { mAngle = - mAngle ; } if ( mListener != null ) { mListener . onSliderMoved ( ( mAngle - mStartAngle ) / ( 2 * Math . PI ) ) ; } }
target:  Invoked when slider starts moving or is currently moving. This method calculates and sets position and angle of the thumb.