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Therefore, the graphics mode command uses two numbers for
reserving columns.
To figure the number of columns reserved, multiply the second
number by 256 and add it to the first number. Since the command is set
up for two numbers, you must supply two numbers even if you need
only one. When you need fewer than 256 columns, just make
nJ
the
number of columns you are reserving and make n2 a zero.
For example, if you wish to send 1632 columns of graphics data,
nl
should be 96 and n2 should be 6 because 1632 = 96 + (6 x 256).
The LQ will interpret the number of bytes determined by
nl
and n2
as graphics data, no matter what codes they are. This means that you
must be sure to supply enough bytes of graphics data or the LQ will
stop and wait for more
data
and will seem to be locked. If, on the other
hand, you supply too much graphics data, the excess will be interpreted
and printed as regular text.
First graphics program
This first program is a simple example to show you how the graphics
command, column reservation numbers, and data can be used in a
BASIC program. Type in and run the following program: be especially
careful to include both semicolons. The program produces the printout
you see below
it.
10
WIDTH "LPT1:",255
20
LPRINT CHR$(27)"+"CHR$(32
(40) CHR$(0);
30
FOR X=1 TO 120
40
LPRINT CHR$(li'B);
50
NEXT
X
) CHR$
Line 20 selects single-density 24-pin graphics (mode 32 from Table
6-1) and also reserves 40 columns for graphics. Since 24pin graphics
requires three bytes of data for each column, line 30 begins a loop to
supply 120 bytes of data. Line 40 contains the number 170 that
produces the first pin pattern shown in Figure 6-2, and line 50 finishes
the loop.
6-6
Graphics and User-defined Characters