+ * Find the visible column which is a given visible number of columns to the
+ * left of another visible column. i.e. for a startColumn x, the column which
+ * is distance 1 away will be column x-1.
+ *
+ * @param visibleDistance
+ * the number of visible columns to offset by
+ * @param startColumn
+ * the column to start from
+ * @return the position of the column in the visible alignment
+ */
+ public int subtractVisibleColumns(int visibleDistance, int startColumn)
+ {
+ int distance = visibleDistance;
+
+ // in case startColumn is in a hidden region, move it to the left
+ int start = adjustForHiddenColumns(findColumnPosition(startColumn));
+
+ // get index of hidden region to left of start
+ int index = getHiddenIndexLeft(start);
+ if (index == -1)
+ {
+ // no hidden regions to left of startColumn
+ return start - distance;
+ }
+
+ // walk backwards through the alignment subtracting the counts of visible
+ // columns from distance
+ int[] region;
+ int gap = 0;
+ int nextstart = start;
+
+ while ((index > -1) && (distance - gap > 0))
+ {
+ // subtract the gap to right of region from distance
+ distance -= gap;
+ start = nextstart;
+
+ // calculate the next gap
+ region = hiddenColumns.get(index);
+ gap = start - region[1];
+
+ // set start to just to left of current region
+ nextstart = region[0] - 1;
+ index--;
+ }
+
+ if (distance - gap > 0)
+ {
+ // fell out of loop because there are no more hidden regions
+ distance -= gap;
+ return nextstart - distance;
+ }
+ return start - distance;
+
+ }
+
+ /**