Radio Shack TRS-80 Operation Manual page 11

computer Graphics Operation Manual
- - - - - - - - - - T R S - B O
® - - - - - - - - - -
be described in detail in the appropriate sections of this
manual.
The Graphics Screen
TRS-8~
Computer Graphics has two "screens" -- Text and
Graphics. (We'll call them screens, although they are really
modes.) Both screens can act independently of each other and
make use of the computer's entire display area.
The Text Screen, also referred to as the "Video Display,"
is
the "normal" screen where you type in your programs. The
Graphics Screen
is
where graphic results are displayed. Both
screens can be cleared independently. Note: The Graphics
Screen will not automatically be cleared when you return to
TRSDOS. It will be cleared when you re-enter BASICG.
The Graphics Screen cannot be displayed at the same time as
the Text Screen.
While working with Computer Graphics, it might be helpful to
imagine the screen as a large Cartesian coordinate plane
(with a horizontal X- and a vertical Y-axis). However,
unlike some coordinate systems,
TRS-8~
Computer Graphics'
coordinate numbering starts in the upper-left corner
(~,~)
-- and increases toward the lower-right corner
(639,239). The lower-left corner
is (~,239)
and the
upper-right corner
is (639,~).
Since the screen is divided into X-Y coordinates (like the
Cartesian system), each pixel is defined as a unique
position. In
TRS-8~
Computer Graphics, you can directly
reference these coordinates as you draw.
About Ranges •••
Some
TRS-8~
Computer Graphics commands accept values within
the Model III integer range (-32768 to 32767), instead of
just
~
to 639 for X and
~
to 239 for Y. Since most of the
points in the integer range are off the screen, these points
are part of what is called Graphics "imaginary" Cartesian
system.
----------Itadlelllaell----------
-9-