204
The
VIC
20
User
Guide
410
POKE
7168,
•••
·
600
MINT
"IfTHIS
IS
F'I
FROG"
·
800
REM
DISPLA¥
F'I
RAB!IT
81e
POKE
7168,
•••
·
900
PRINT
"IfTHIS
IS
F'I
RABBIT"
Messages from BASIC itself may still be a problem:
If
you redefine the
alphabetic characters to build players, a simple READY message may look
like Egyptian hieroglyphics. This should not cause any serious difficulty,
except when you are debugging your program. If you interrupt it with the
STOP key, or if BASIC finds an error, the messages produced may be
somewhat difficult to read. You can return to the normal character set by
POKEing to location 36869 (POKE a value of
192
for a VIC with 8K or
more
of
added memory; use a value of
240
for smaller VICs) and then
POKEing the value required by your program before continuing. You
should also note
that
the RESTORE key will bring back the normal character
set, but leave your custom character memory intact and still protected from
BASIC. Unfortunately, it will also clear the screen and erase the error
message, so it's not very useful while debugging programs.
Animating
Players
A player built from custom characters can
be
made to move by modify-
ing its patterns in character memory, but this technique will usually be too
slow if done in BASIC. (Machine language programs can run fast enough to
handle it.) A simpler and faster approach
is
to
define more than one version
of the player in character memory. Your program can then make it move by
changing the version displayed with a POKE to screen memory.
As
an example of this method of animation,
we
have taken our stick
man and put a little meat on
his
bones by building him with four characters
instead
of
one.
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