onScroll

RotaryKnobView.kt

    override fun onScroll(e1: MotionEvent, e2: MotionEvent, distanceX: Float, distanceY: Float)
            : Boolean {

        val rotationDegrees = calculateAngle(e2.x, e2.y)
        // use only -150 to 150 range (knob min/max points
        if (rotationDegrees >= -150 && rotationDegrees <= 150) {
            setKnobPosition(rotationDegrees)

            // Calculate rotary value
            // The range is the 300 degrees between -150 and 150, so we'll add 150 to adjust the
            // range to 0 - 300
            val valueRangeDegrees = rotationDegrees + 150
                value = ((valueRangeDegrees / divider) + minValue).toInt()
                if (listener != null) listener!!.onRotate(value)
        }
        return true
    }