private void movePos(float deltaY) {
        // has reached the top
        if ((deltaY < 0 && mPtrIndicator.isInStartPosition())) {
            if (DEBUG) {
                PtrCLog.e(LOG_TAG, String.format("has reached the top"));
            }
            return;
        }

        int to = mPtrIndicator.getCurrentPosY() + (int) deltaY;

        // over top
        if (mPtrIndicator.willOverTop(to)) {
            if (DEBUG) {
                PtrCLog.e(LOG_TAG, String.format("over top"));
            }
            to = PtrIndicator.POS_START;
        }

        mPtrIndicator.setCurrentPos(to);
        int change = to - mPtrIndicator.getLastPosY();
        updatePos(change);
    }
if deltaY > 0, move the content down

@param deltaY
ptr-lib/src/in/srain/cube/views/ptr/PtrFrameLayout.java