Radio Shack TRS-80 Operation Manual page 10

Computer Graphics Operation Manual
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PIXEL-.......
Lower resolution
Higher resolution
Figure 1. Resolution
Since the
TRS-8~
has high-resolution --
64~
pixels on the
X-axis
(~
to 639) and
24~
pixels on the Y-axis
(~
to 239)
you can draw displays that have excellent clarity and
detail.
How
TRS-8~
Computer Graphics Works
The concept of graphics is fairly simple. Each point on the
screen can be turned ON (white) or OFF (black).
When you clear the Graphics Screen, all graphic points are
turned OFF.
Therefore, by setting various combinations of the pixels
(usually with a single command) either ON or OFF, you can
generate lines, circles, geometric figures, pictures, etc.
The Graphics Subroutine Library, which is part of the
Computer Graphics package, contains subroutines which
provide the same capabilities, as well as similar names and
parameters, as the commands and functions in Graphics BASIC.
The main difference between the Subroutine Library and
BASICG is the manner in which coordinates are specified
(e.g., BASICG coordinates are specified as arguments for
each command while the Subroutine Library specifies
coordinates with a separate subroutine call). Another
difference concerns the names of a few routines (e.g., LINE
vs. LINEB vs. LINEBF, etc.). All of these differences will
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-8-