Radio Shack TRS-80 User Manual page 135

Chapter 22
Advanced
Graphics
Remember
the bouncing dot? Wouldn't
it
be
nifty
if
we
could
get the screen
to
say
"PING"
each time
the dot
bounced
off
the
barrier?
Well / think
it
would be
nifty,
so we're going to
do
it.
But
first
. . .
We
learned
all
about
SET
and
RESET
earlier.
Now
we
will learn
about
PRINT
AT—
a special
type of
PRINT
statement
especially useful in graphics,
and
POINT(X.Y)
—
a quite unrelated statement
which
allows us to look
at
any
of the
6144
graphic
block
locations
and
get
an answer
to the question
"which
ones
are
ON
and which
are
OFF?"
A
super
powerful
statement,
and
it's
even useful!
I
thought you
printed
ON,
not
printed
AT
Learn something
new
every
day.
The
PRINT
AT
(also
written
PRINT AT
and
P.
AT)
state-
ment
allows us to begin printing
starting at a
location
number. Example,
type:
10
CLS
50
PRINT
AT 200,
"
HELLO THERE
200,
WHEREVER
YOU
ARE."
.
.
.
and
RUN.
Where
is
200? Back
to the Radio Shack
graphics
layout
chart
(Video
Display Worksheet).
If
you
don't
have one handy,
there's
one back
in
Chapter
20.
With
the aid of an ordinary household electron microscope, the
words "PRINT
AT"
are
clearly
seen
on
the
upper
left
hand
corner of the
sheet.
Also, an arrow pointing to
a set of
numbers. Further scrutiny
discloses
a tiny
"X",
obviously
referring
to the address numbers
on
the
"X"
Street
—
and
a tiny
"Y"
pointing to the
"Y"
numbers
for
"Y"
Avenue.
A
truly
astute researcher
will also see the
"TAB"
numbers
—
all
64
of
them
(starting
with
0).
The
PRINT AT
numbers
start at
and go through 63
—
in
the
first line.
They
then pick up
on
the second
line
with
#64
and continue through #127.
The
third line
starts
with #128,
etc.
The
PRINT
AT
divisions are really the
same
as
those
for
TAB
except
PRINT AT
does not
start
over again with zero on
the
second
line. It
keeps going
right
on through
PRINT
posi-
..yanloft
oar attempt
at
humor l'^£oMng
a little
fun at ourselves here.
.!
133