pin our visible content bounds to the bounds of the doc itself, to account for overscroll

    // Sets r to be our visible rectangle in content coordinates

    private void calcOurContentVisibleRect(Rect r) {

        calcOurVisibleRect(r);

        r.left = viewToContentX(r.left);

        // since we might overscroll, pin the rect to the bounds of the content

        r.left = Math.max(viewToContentX(r.left), 0);

        // viewToContentY will remove the total height of the title bar.  Add

        // the visible height back in to account for the fact that if the title

        // bar is partially visible, the part of the visible rect which is

        // displaying our content is displaced by that amount.

        r.top = viewToContentY(r.top + getVisibleTitleHeight());

        r.right = viewToContentX(r.right);

        r.bottom = viewToContentY(r.bottom);

        r.top = Math.max(viewToContentY(r.top + getVisibleTitleHeight()), 0);

        r.right = Math.min(viewToContentX(r.right), mContentWidth);

        r.bottom = Math.min(viewToContentY(r.bottom), mContentHeight);

    }

    static class ViewSizeData {