HP 7470A Interfacing And Programming Manual page 49

)
)
)
45 DEGREE CHORD ANGLE 30 DEGREE CHORD ANGLE
15 DEGREE CHORD ANGLE 5 DEGREE CHORD ANGLE
The circle instruction includes an automatic pen down feature. When a
circle command is received, the pen lifts (if it was down), moves from
the center of the circle to the circle starting point on the circumference,
lowers the pen, draws the circle, then returns, pen up, to the center of
the circle. After drawing the circle, the pen assumes the pen state (up or
down) that was in effect prior to the circle command. To avoid drawing
lines to the center of the circle, move to and away from the circle's
center with the pen up.
Circles are drawn within the defined window, with clipping occurring
outside the window limits. Drawing circles within the window conforms
to the definitions given for plotting under the PA instruction.
Each chord of the circle is drawn using the currently defined line type.
Refer to The Line Type Instruction, LT, in Chapter 4.
To demonstrate some of the features of the circle instruction, the follow­
ing strings of HP-GL instructions draw various circles with different
line types, radii, and starting points.
" I N ; S P 1 ; I P 2 G 5 0 , 1 3 2 5 , 7 6 5 0 , 6 3 2 5 ; "
" S C - 1 0 0 , 1 0 0 , - 1 0 0 , 1 0 0 ; "
" P R O , 0 ; L T ; C I 1 0 , 5 ; L T O ; C I - 2 0 , 5 ; L T 1 ; C I 3 0 , 5 ; "
" L T 2 ; C I - 4 0 , 5 ; L T 3 ; C I 5 0 , 5 ; L T 4 ; C I - G O , 5 ; L T 5 ;
C I ? 0 , 5 ; L T 6 ; C I 8 0 , 5 ; "
4 CONTROLLING THE PEN AND PLOTTING
/ / 1
! I I
I
I
' /
\ \ \ \ \
\ \ \
x
■
— \
\ \ \ \ \
\ M \ \
I I 1 I I
/ / / / /
/ / / / /
y// /
y
/
/
The following BASIC program shows that the circle instruction can
also be used to define a series of circles that must be repeated in a
particular pattern.
10 PRINTER I S 10
20 PRINT " I N ; S P 1 ; I P 2 6 5 0 , 1 3 2 5 , 7 6 5 0 , G 3 2 5 ; "
30 PRINT " S C - 1 0 0 0 , 1 0 0 0 , - 1 0 0 0 , 1 0 0 0 ; " -
40 PRINT " P f l - 8 0 0 , 8 0 0 ; "
50 GOSUB 130
60 PRINT " P f l 2 0 0 , 8 0 0 ; "
70 GOSUB 130
80 PRINT " P f l - 8 0 0 , - 2 0 0 ; "
90 GOSUB 130
100 PRINT "PFI200, - 2 0 0 ; "
110 GOSUB 130
120 END
130 PRINT " C I 5 0 ; P R 6 0 0 , 0 ; C I 5 0 ; P R - 3 0 0 , - 3 0 0 ; C I 2 5 0 ; "
140 PRINT " P R - 3 0 0 , - 3 0 0 ; C I 5 0 ; P R 6 0 0 , 0 ; C I 5 0 ; "
150 RETURN
Line 10 defines the select code of the interface; change this statement
as necessary for your computer.
CONTROLLING THE PEN AND PLOTTING 3-15