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The first line of the program specifies single-density graphics for 40
columns:
l00 LPRINT CHR$(27);"K";CHR$(40);CHR$(0);
The second line is the data that is printed as pin patterns. It uses the
number
74
to produce one of the patterns shown above. The FOR-NEXT
loop sends 40 columns of data.
Here is the second line of data:
200 FOR X=1 TO
40:
LPRINT CHR$(74);: NEXT X
That is the whole program. In BASIC, semicolons at the ends of the lines
are very important; they prevent the computer from sending other codes
after the ones you specify. In other languages you may have to use a
special command to send a single code at a time. Run the program to see
the result below. Although it is not as interesting as the examples at the
beginning of this chapter, it shows exactly how the graphics mode works.
WIDTH statements
Some software programs (including most versions of BASIC)
automatically insert carriage return and line feed codes after every 80 or
130 characters. This is usually no problem with text, b&t can spoil your
graphics. Two extra columns of graphics are printed in the middle of the
ones you send, and two data numbers are left over and printed as text.
In some versions of BASIC you can prevent unwanted control codes in
graphics by putting a WIDTH statement at the beginning of all graphics
programs. The format in many forms of BASIC is either WIDTH
“LPTl:“, 255 or WIDTH LPRINT 255. Check your software manual for
the proper format.
Printing taller patterns
The next example shows how several lines of graphics can be formed
into a figure taller than eight dots. It uses programming techniques for
producing textured or repetitive patterns.
Using Software and Graphics
4-13