1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
|
<html lang="en">
<head>
<title>Point sweeps - Sketch</title>
<meta http-equiv="Content-Type" content="text/html">
<meta name="description" content="Sketch">
<meta name="generator" content="makeinfo 4.7">
<link title="Top" rel="start" href="index.html#Top">
<link rel="up" href="Swept-objects.html#Swept-objects" title="Swept objects">
<link rel="prev" href="Swept-objects.html#Swept-objects" title="Swept objects">
<link rel="next" href="Polyline-sweeps.html#Polyline-sweeps" title="Polyline sweeps">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
Copyright (C) 2005, 2006, 2007, 2008 Eugene K. Ressler.
This manual is for `sketch', version 0.2 (build 131),
Saturday, August 09, 2008, a program that converts descriptions of simple
three-dimensional scenes into static drawings. This version generates
`PSTricks' or `PGF/TikZ' code suitable for use with the
TeX document processing system.
`Sketch' is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
Sketch is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with `sketch'; see the file COPYING.txt. If not, see
http://www.gnu.org/copyleft.-->
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
pre.display { font-family:inherit }
pre.format { font-family:inherit }
pre.smalldisplay { font-family:inherit; font-size:smaller }
pre.smallformat { font-family:inherit; font-size:smaller }
pre.smallexample { font-size:smaller }
pre.smalllisp { font-size:smaller }
span.sc { font-variant:small-caps }
span.roman { font-family: serif; font-weight: normal; }
--></style>
</head>
<body>
<div class="node">
<p>
<a name="Point-sweeps"></a>Next: <a rel="next" accesskey="n" href="Polyline-sweeps.html#Polyline-sweeps">Polyline sweeps</a>,
Previous: <a rel="previous" accesskey="p" href="Swept-objects.html#Swept-objects">Swept objects</a>,
Up: <a rel="up" accesskey="u" href="Swept-objects.html#Swept-objects">Swept objects</a>
<hr><br>
</div>
<!-- node-name, next, previous, up -->
<h4 class="subsection">2.7.1 Point sweeps</h4>
<p>Sweeping a point makes a one-dimensional path, which is a polyline.
Since we have swept with a rotation, the result is a circular arc.
Here is what it looks like.
<div align="center"><img src="ex070.png" alt="ex070.png"></div>
<p>This is the first example we have seen of <code>sketch</code> arithmetic.
The expression <tt>180 / n_segs</tt> causes the eight rotations to add
to 180. If you're paying attention, you'll have already noted that
there are <em>nine</em> points, producing eight line segments.
<p>You can cause the swept point to generate a single polygon rather than
a polyline by using the <dfn>closure tag</dfn> <tt><></tt>
<a name="index-_003c_003e_0040r_007b_002c-closure-tag_007d-100"></a><a name="index-closure-tag_002c-_0040code_007b_003c_003e_007d-101"></a>after the number
of swept objects. Code and result follow
<a name="index-def-102"></a><a name="index-rotate-103"></a><a name="index-sweep-104"></a>
<pre class="verbatim">
def n_segs 8
sweep { n_segs<>, rotate(180 / n_segs, (0,0,0), [0,0,1]) } (1,0,0)
</pre>
<div align="center"><img src="ex080.png" alt="ex080.png"></div>
</body></html>
|