Commodore Plus 4 - Page 102

POINTS,
LINES,
AND
LABELS
Type the commands GRAPHIC 2,1: DRAW 1,0,0 and hit RETURN
Look closely at the upper left corner of the screen. The Plus/4 drew a
black dot there.
In the DRAW command, the first number is either 1 (foreground color)
or 0 (background). The next two numbers are for the row and column
positions for the dot. So if you wanted to draw a dot at column 17, row
20, just type DRAW 1,17,20. To erase the same dot type DRAW 0,17,20.
The DRAW command can also draw a line between any two points.
Just add the word TO and the coordinates of the other end, like this:
DRAW 1,1,1 TO 100,100. This draws a line from 1,1 to 100,100.
If you are used to drawing graphs in math, you might get a little con
fused at first while using the computer. The coordinate system in the
Plus/4
is different from what you're used to. In math the 0,0 point would
either be at the center or the lower left corner of the screen, but on the
computer it is the upper left corner. You'll get used to the system in the
computer as you practice.
Once you have put a point or line on the screen, you can draw a line
from it to any other point like this: DRAW 1 TO 150,50. This draws a line
from the last point drawn to column 150, row 50. If your program uses a
lot of DRAW TO commands, you could place the first dot at a position
on the sc/een by using the LOCATE command, as in LOCATE 100,100.
The DRAW command can have several forms, such as:
COMMAND
RESULT
DRAW color source, column, row
DRAW color source, column, row TO column, row
DRAW color source TO column, row
POINT
LINE
LINE DRAWN
FROM LAST POINT
Color source is 0 for the background, 1 for the foreground
To erase points or lines on the screen, use the DRAW command fol
lowed by the number 0. If you created a point with DRAW 1,1,1, you can
erase it with DRAW 0,1,1. A line created with DRAW 1,1,1 TO 100,100 is —
erased by DRAW 0,1,1 TO 100,100.
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