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Amiga Plus Extra 1996 #6
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AmigaPlus-eXtra-6-96.iso.7z
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AmigaPlus-eXtra-6-96.iso
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programme
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a-render
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doc
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convex_polygons.doc
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CONVEX_POLYGONS.DOC
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This is the definition of a convex polygon vs. a concave polygon. You
will need to know how to distinguish between the two before you can use the
program Digi.
The difference is fairly simple. For aid with the explanation, see the
demo picture CONVEX.POLYGONS. The picture shows examples of convex and
concave polygons.
Since A-Render can only work with convex polygons, one of the basic
purposes of Digi is to break up a concave polygon into a number of convex
polygons. We define these convex polygons by outlining each polygon. In
the example drawing, the concave polygons have been divided with grey
lines to indicate the boundaries of the convex polygons. Digi will also
display polygon boundaries as grey lines.
The best way to determine whether a polygon is convex or concave is to
look at the sides of the polygon. If two sides make the polygon 'cave-in'
at one point or more, the polygon is concave. Otherwise, if none of the
sides cave-in, the polygon is convex. In other words, a concave polygon
is dented, while a convex polygon has no dents.
Refering to the upper concave polygon in the picture, the solid grey line
shows the only possible division to divide it into convex polygons. The
lower concave polygon has two dashed grey lines, indicating that either
line could be used to split up this polygon. Although you could split it
into three concave polygons, it is best to keep the number as low as
possible.