13B
User's
Handbook
to
the Atari 400/ 800
Computers
character graphics
mode
1 and 2, the
COLOR
data indicates the
character and
color
register
of
a PLOT statement.
In
graphics modes 3
through
8,
the
COLOR
data actually
corresponds
to
the
color
register
of
a
picture
element.
EXAMPLE
10
GRAPHICS 3
20
COLOR
2
30
PLOT 0,0
40
DRAWTO
35,0
50
LOCATE 5, 0, X
60
PRINT X
The previous
example consists
of
a
program
that
uses
the
LOCATE statement. Line
10
chooses graphics
mode
3.
Line
20
indicates that
color
register 2
is
used in the PLOT and
DRAWTO
statements. Since
no
SETCOLOR statement
was
executed, the
default
color
(green)
is
used. The PLOT statement at line
30
illuminates a
green
picture
element
at the
upper
left
corner
of
the
screen. The
DRAWTO
statement at
line
40
illuminates the
top
row
of
the display in the same
color.
Line
50
is
a LOCATE
statement that places the cursor at position
5,0.
Since the
line
was
drawn
from
0,0
to
35,0, the position 5,0
is
an
illuminated
picture
element.
The value
of
the
color
register at that position
is
2.
The
LOCATE statement assigns
the
color
register value
(2)
to the
variable X. Line
60
is
a PRINT statement that displays the value
of
X.
The
DRAWTO
and XIO statements have separate
memory
locations
for
the
cursor position.
As
a result, a LOCATE statement
has
no
effect
on
the cursor position
of
a
DRAWTO
or
XIO
statement.
When
LOCATE
is
used
to
read a code
from
the screen,
the
cursor
will
move
one
location
to
the right. If the cursor
was
on
that last
column
of
a
row
when LOCATE
was
executed, the cursor may
attempt
to
advance
to
the first
column
of
the next
row
resulting
in
Error
141
(Cursor
Out
of
Range).
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