Radio Shack TRS-80 X-PAD GT-116 - Marginally Speaking; The Cartesian System According to X-Pad

Figure
4.
X-Pad
Display
Area vs. Screen
Display Area
Anytime
the Pen
moves
onto
the X-Pad's
Display Area
(see
Figure
6 later in this
manual, as well),
a graphics
display
will
appear
on
the
Screen.
(You can
also
use this
area
to
create a menu,
but
it is primarily
designed for
display
only!)
The
Menu
Area,
which
is
the margin
area
and which runs
around
the
perimeter of the Display Area
(about
1"
from
the edge
all
around),
works differently.
The X-Pad will
send
signals from
that
area
but will
not
display anything
on
the
Screen,
Nevertheless,
this
Area
is
extremely
powerful.
For
instance,
you
might assign
various
Extended
Color BASIC commands to
sections
in the Menu
Area. Then, instead of
typing
in a command (such as
PAINT)
from
the Keyboard, just touch
with
the Pen
that
part of
Menu
assigned to
PAINT
and
that
statement will
be the
next
one
used.
You can
think
of the Display Area of the
X-Pad
as having
an
imaginary
Cartesian
coordinate
(point-plotting)
system.
The
range
for X
is
to
255
and
the
range for Y
is
to
191.
The
upper-left
corner
is
the
origin
(0,0),
the
upper-right
corner
is
(255,0),
the
lower-left
corner is
(0,191)
and
the
lower-right
corner is
(255,191),
The
centerpoint is
(127,95),
On
the
Writing
Surface,
X
and Y
are measured
by the
X-Pad
in
"increments"
or individual units of
calibration.
Each
of these
increments
represents
one pixel
on
the
Color
Computer's
Graphic
Screen.
Marginally Speaking
.
.
.
In
the
Menu
Area,
there
are
three
types
of margins
on
the
Writing
Surface
of
the X-Pad:
•
X-Margin,
the
left
and
right
vertical
margins.
•
Y-Margin,
the top
horizontal margin.
•
Bottom Margin, the bottom
horizontal
margin but
can
be defined by
your
program.
(0,0)
(255,0)
V+y
(0,191)
(255,1911
10,200)
1255,2001
Figure
5.
X-PacTs
Margins
and
Cartesian
System
The Cartesian
System
According
to
X-Pad
We've
already
talked
about the
X-Pad
Cartesian
system.
Bat
since
you now
know about X-Y
coordinates,
here
are
some
more
important
facts about
X-Pad's plotting
system:
•
The center of
the
Cartesian system
is
(127,95).
•
If
you
move
the
Pen beyond the
range
(into a
margin,
10