private int getScrollYForPage(int whichPage) {
		int height = 0;
		for (int i = 0; i < whichPage; i++) {
			final View child = getChildAt(i);
			if (child.getVisibility() != View.GONE) {
				height += child.getHeight();
			}
		}
		return height - pageHeightPadding();
	}
Gets the value that getScrollX() should return if the specified page is
the current page (and no other scrolling is occurring). Use this to pass
a value to scrollTo(), for example.

@param whichPage
@return
app/src/main/java/pro/alexzaitsev/freepager/library/view/core/VerticalPager.java