As a brief aside on FILL routines – You can always tell a recursive based
FILL routine, as, when it is filling a complex area, there are often pauses
while nothing apparently happens on the screen. What is actually happening is
that the FILL routine has just filled to a ‘dead end’, and there then follows
a period where the recursive structure ‘unwinds’ itself, returning from layer
to layer back up the stack until it finds an area that it has not yet filled.
BUG TIME
Well folks, it had to happen. Between writing the first part of this
article and completing this one someone has unearthed a bug that is present in
both the
IVC
and
SVC
monitors. That fact that it has taken so long to surface
is indicative that none of you are likely to have met it yet (otherwise you
would have reported it – wouldn’t you?). It is in the ESC “f” … sequence
that allows you to redfine the function keys from a program. If you try and
‘undefine’ a key using this sequence the key is not actually fully deleted
from the function key table, and if the key is subsequently pressed something
will be returned to the host system. What the ‘something’ is cannot be easily
predicted. Key definitions can be removed totally from the table, but only by
using the Shift/Edit feature direct from the keyboard.
TABLE 1: Extra features of the SVC