+find_up_cursor_position = (tree, cursor, ideal_x) ->
+ new_cursor = cursor
+ # go prev until we're higher on y axis
+ while new_cursor.y >= cursor.y
+ new_cursor = find_prev_cursor_position tree, new_cursor
+ return null unless new_cursor?
+ # done early if we're already left of old cursor position
+ if new_cursor.x <= ideal_x
+ return new_cursor
+ target_y = new_cursor.y
+ # search leftward, until we find the closest position
+ # new_cursor is the prev-most position we've checked
+ # prev_cursor is the older value, so it's not as prev as new_cursor
+ while new_cursor.x > ideal_x and new_cursor.y is target_y
+ prev_cursor = new_cursor
+ new_cursor = find_prev_cursor_position tree, new_cursor
+ break unless new_cursor?
+ # move cursor to prev_cursor or new_cursor
+ if new_cursor?
+ if new_cursor.y is target_y
+ # both valid, and on the same line, use closest
+ if (ideal_x - new_cursor.x) < (prev_cursor.x - ideal_x)
+ return new_cursor
+ else
+ return prev_cursor
+ else
+ # new_cursor on wrong line, use prev_cursor
+ return prev_cursor
+ else
+ # can't go any further prev, use prev_cursor
+ return prev_cursor
+
+find_down_cursor_position = (tree, cursor, ideal_x) ->
+ new_cursor = cursor
+ # go next until we move on the y axis
+ while new_cursor.y <= cursor.y
+ new_cursor = find_next_cursor_position tree, new_cursor
+ return null unless new_cursor?
+ # done early if we're already right of old cursor position
+ if new_cursor.x >= ideal_x
+ # this would be strange, but could happen due to runaround
+ return new_cursor
+ target_y = new_cursor.y
+ # search rightward, until we find the closest position
+ # new_cursor is the next-most position we've checked
+ # prev_cursor is the older value, so it's not as next as new_cursor
+ while new_cursor.x < ideal_x and new_cursor.y is target_y
+ prev_cursor = new_cursor
+ new_cursor = find_next_cursor_position tree, new_cursor
+ break unless new_cursor?
+ # move cursor to prev_cursor or new_cursor
+ if new_cursor?
+ if new_cursor.y is target_y
+ # both valid, and on the same line, use closest
+ if (new_cursor.x - ideal_x) < (ideal_x - prev_cursor.x)
+ return new_cursor
+ else
+ return prev_cursor
+ else
+ # new_cursor on wrong line, use prev_cursor
+ return prev_cursor
+ else
+ # can't go any further prev, use prev_cursor
+ return prev_cursor
+