Atari 65XE Owner's Manual page 78

Graphics Mode 3
The graphics mode 3 screen is a grid consisting of 40 columns and 24
rows (20 if you use the text window). Enter and run the following
program:
NEW
10 GRAPHICS 3
20 COLOR 1
30 PLOT 0,0
RUN
In the upper left corner is an orange block. The block, or pixel, is one
unit in the graphics screen. The COLOR command determines the
color of the pixel. The number after the COLOR command determines
which color register to use for the color of the pixel. The COLOR com-
mand does not place a color in the register; SETCOLOR does that. The
COLOR command simply selects which register to use to plot the
pixel, and the pixel becomes whatever color is in the register. To make
this clearer, change line 20 to
20 COLOR 2
Run the program. The orange pixel is now light green. Think of each
pixel as a text character. In modes 1 and 2, you used uppercase and
lowercase characters and Inverse Video to select the colors of the
text. In modes 3 and above, use the COLOR command to select the
color for the pixels.
PLOT: Plotting Points on the Grid
PLOT is like the PRINT #6; command except that it prints pixels in-
stead of letters and numbers. COLOR is like the upper/lower/inverse
color selection method; it selects the register. The default colors are
orange, light green, dark blue, and black. To change the color in any
of the registers, use the SETCOLOR command.
The color registers are like four buckets of paint. SETCOLOR selects
the color that goes into each of the four buckets, and COLOR selects
the bucket into which the paintbrush will be dipped. PLOT determines
where the brush will be positioned on the screen.
DRAWTO: Connecting the Dots
Add this line:
40 DRAWTO 39,0
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