Radio Shack TRS-80 Operation Manual page 56

Computer Graphics
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®
VIEW (command)
Redefines the Screen (Creates a Viewport)
Operation Manual
VIEW creates a "viewport" which redefines the screen
parameters
(~-639
for X and
~-239
for Y). This defined area
then becomes the only place you can draw graphics displays.
If you enter more than one viewport, you can only draw
displays in the last defined viewport.
Since VIEW redefines the SCREEN:
CLR clears the interior of the viewport only.
If you PSET or PRESET points, draw circles, etc.,
beyond the parameters of the currently defined
viewport, only the portions that are in the viewport
will be displayed.
If you try to read a point beyond the viewport (with
POINT), it will return a-I.
You can only GET and PUT arrays within the viewport.
You can't PAINT outside the viewport.
The upper-left corner of the viewport is read as
(~,~)
(the
"relative origin") when creating items inside the viewport.
All the other coordinates are read relative to this origin.
However, the "absolute coordinates" of the viewport, as they
are actually defined on the Graphics Cartesian system, are
retained in memory and can be read using VIEW as a function.
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