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Note that this is strictly for ease of identification, and has no |
69 |
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real meaning as far as the geometric description goes. In contrast, |
70 |
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the transform entity is very significant as it determines how enclosing |
71 |
< |
objects are to be scaled and placed in the final description. |
71 |
> |
objects are to be scaled and placed in the final description. Hierarchical |
72 |
> |
contexts may be nested in any way, but should not overlap. |
73 |
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|
74 |
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Without further ado, here are the proposed entities and their interpretations: |
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|
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sph vc radius sphere |
98 |
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cyl v1 radius v2 truncated right cylinder (open-ended) |
99 |
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cone v1 rad1 v2 rad2 truncated right cone (open-ended) |
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< |
prism v1 v2 v3 .. length right prism (closed solid) |
100 |
> |
prism v1 v2 v3 .. length truncated right prism (closed solid) |
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|
ring vc rmin rmax circular ring with inner and outer radii |
102 |
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torus vc rmin rmax circular torus with inner and outer radii |
103 |
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xf [xform] begin/end transformation context |
145 |
|
That is, with the thumb of the right hand pointing in the direction |
146 |
|
of the axis, rotation follows the curl of the fingers. |
147 |
|
|
148 |
< |
The transform command itself is also cumulative, and a transform |
149 |
< |
command with no arguments is used to return to the previous |
150 |
< |
condition. It is necessary that transforms and their end statements |
151 |
< |
("xf" by itself) be balanced in a file, so that later or enclosing |
152 |
< |
files are not affected. |
148 |
> |
The transform command itself is also cumulative, but in the reverse |
149 |
> |
order. That is, later transformations (i.e. enclosed transformations) |
150 |
> |
are prepended to existing (i.e. enclosing) ones. A transform command |
151 |
> |
with no arguments is used to return to the previous condition. It is |
152 |
> |
necessary that transforms and their end statements ("xf" by itself) be |
153 |
> |
balanced in a file, so that later or enclosing files are not affected. |
154 |
|
|
155 |
|
Transformations apply only to geometric types, e.g. polygons, spheres, etc. |
156 |
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Vertices and the components that go into geometry are not directly affected. |
263 |
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and a length value. The prism will be extruded so that the end-face |
264 |
|
points outward, unless the length value is negative, in which case the |
265 |
|
object is extruded in the opposite direction, resulting in inward- |
266 |
< |
directed surface normals. |
266 |
> |
directed surface normals. If surface normals are specified for the |
267 |
> |
vertices, they will be applied to the side faces but not the end |
268 |
> |
faces, and they must generally point in the appropriate direction |
269 |
> |
(i.e. in or out depending on whether extrusion is negative or positive). |
270 |
|
|
271 |
|
A sphere, cylinder or cone with negative radii is interpreted as having |
272 |
|
an inward facing surface normal. Otherwise, the normal is assumed |