h6. [[OS SWI Calls]] h6(. » [[OS_ChangedBox]] h6((. » Block |_<^{width:3em}. Offset |_<^. Contents | |>^. +0|<^. New disable/enable flag | |>^. +4|<^. X co-ordinate of left edge of box | |>^. +8|<^. Y co-ordinate of bottom edge of box | |>^. +12|<^. X co-ordinate of right edge of box | |>^. +16|<^. Y co-ordinate of top edge of box | h4. Notes The data pointed to by R1 on exit at offsets 4 - 16 are only valid if the change box calculations were in an enabled state immediately after the call; otherwise they are undefined. This call checks which areas of the screen were changed by VDU commands and returns the smallest rectangle which covers all changed pixels. h4. See also * [[OS_ChangedBox]]