private boolean isWithinDeltaOfScreen(View descendant, int delta, int height) {
        descendant.getDrawingRect(mTempRect);
        offsetDescendantRectToMyCoords(descendant, mTempRect);

        return (mTempRect.bottom + delta) >= getScrollY()
                && (mTempRect.top - delta) <= (getScrollY() + height);
    }
@return whether the descendant of this scroll view is within delta
 pixels of being on the screen.
app/src/main/java/home/smart/fly/animations/widget/NestedScrollView.java