Microcomputer Graphics

26 Microcomputer Graphics
The FOR loop beginning in line 30 references memory locations
8192, 9216, 10240, 11264, 12288, 13312, and 14366. The contents of
these memory locations are displayed below one another at the top left
corner of the screen . As a result of the loop in lines 30 through 70, the
contents of these memory locations will be as follows:
Memory Location Bit Pattern (reversed) Display
Decimal
Binary
8192 8 0001000
9216 20 0010100
10240
11264
34
34
0100010
0100010
12288 62 0111110
13312 34 0100010
14366 34 0100010
Figure 2.6
As the contents of these memory locations are displayed on the screen,
they create the image of the letter "A."
The discussion above suggests a means by which text may be displayed
on the graphics screen easily. More detail will be given in Chapter
3. For the present, we will identify procedures that define additional
characters.
Map the character or symbol on a grid; 7 x 7 works well. For example,
to obtain the letter "Z," convert each of the bit patterns to a
number code, as has been done in Figure 2. 7. Then POKE the bit pattern
into memory. Memory locations may be identified from Figure
2.4.
To continue the example, we may display the symbols "A" and
"Z" side-by-side in the top left corner of the screen using Program
2.2.
Program 2.2: BIT PATTERN CHARACTERS
1 REM PROGRAM 2.2 (BIT PA TTERN CHARAC TERS)
2 REM PLAC ES LETTERS A AN D Z ON THE HI RES
SC REEN