Radio Shack TRS-80 Operation Manual page 22

computer Graphics Operation Manual
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You can have a positive start and a negative end (or
vice versa) as well as negative starts and ends. In
these cases, only one radius line is drawn.---
Center
Figure 9. CIRCLE's (+) start, (-) end
Hints and Tips about start and end:
When using the default values for start and end,
you must use commas as delimiters if you wish to add
more parameters.
If you use PI, it is not a reserved word in BASICG and
must be defined in your program.
ar
Aspect Ratio
You can draw ellipses by varying the aspect ratio from the
default value
(.5)
for a circle (and semicircle).
Every ellipse has a "major axis" which is the ellipse's
longer, predominant axis. with an ellipse (as with a
circle), the two axes are at right angles to each other.
The mathematical equation for determining the aspect ratio
is:
ar
=
length of Y-axis/length of X-axis
If the aspect ratio is .5, a circle is drawn.
If the ratio is less than .5, an ellipse with a major
axis on the X-axis is drawn.
If the ratio is greater than .5, an
~llipse
with a major
axis on the Y-axis is drawn.
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