HCoop / clinton / guile-figl.git / blame
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1 | <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "xhtml1-transitional.dtd"> |
| 2 | <!-- saved from url=(0013)about:internet --> | |
| 3 | <?xml-stylesheet type="text/xsl" href="mathml.xsl"?><html xmlns="http://www.w3.org/1999/xhtml" xmlns:pref="http://www.w3.org/2002/Math/preference" pref:renderer="mathplayer-dl"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>gluBeginTrim</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /></head><body><div class="refentry" lang="en" xml:lang="en"><a id="gluBeginTrim"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>gluBeginTrim — delimit a NURBS trimming loop definition</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">gluBeginTrim</b>(</code></td><td>GLUnurbs* </td><td><var class="pdparam">nurb</var><code>)</code>;</td></tr></table></div></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0"><tr><td><code class="funcdef">void <b class="fsfunc">gluEndTrim</b>(</code></td><td>GLUnurbs* </td><td><var class="pdparam">nurb</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>nurb</code></em></span></dt><dd><p> | |
| 4 | Specifies the NURBS object (created with <a class="citerefentry" href="gluNewNurbsRenderer.xml"><span class="citerefentry"><span class="refentrytitle">gluNewNurbsRenderer</span></span></a>). | |
| 5 | </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p> | |
| 6 | Use <code class="function">gluBeginTrim</code> to mark the beginning of a | |
| 7 | trimming loop and <a class="citerefentry" href="gluEndTrim.xml"><span class="citerefentry"><span class="refentrytitle">gluEndTrim</span></span></a> to mark the end | |
| 8 | of a trimming loop. A trimming loop is | |
| 9 | a set of oriented curve segments (forming a closed curve) that | |
| 10 | define boundaries of a NURBS surface. You include these | |
| 11 | trimming loops in the definition of a NURBS | |
| 12 | surface, between calls to <a class="citerefentry" href="gluBeginSurface.xml"><span class="citerefentry"><span class="refentrytitle">gluBeginSurface</span></span></a> and <a class="citerefentry" href="gluEndSurface.xml"><span class="citerefentry"><span class="refentrytitle">gluEndSurface</span></span></a>. | |
| 13 | </p><p> | |
| 14 | The definition for a NURBS surface can contain many | |
| 15 | trimming loops. For example, if you wrote a definition | |
| 16 | for a NURBS surface that resembled a rectangle with | |
| 17 | a hole punched out, the definition would contain two | |
| 18 | trimming loops. One loop would define the outer edge | |
| 19 | of the rectangle; the other would define | |
| 20 | the hole punched out of the rectangle. The definitions | |
| 21 | of each of these trimming loops would be bracketed by a | |
| 22 | <code class="function">gluBeginTrim</code>/<a class="citerefentry" href="gluEndTrim.xml"><span class="citerefentry"><span class="refentrytitle">gluEndTrim</span></span></a> pair. | |
| 23 | </p><p> | |
| 24 | The definition of a single closed trimming loop can consist | |
| 25 | of multiple curve segments, each described as a piecewise | |
| 26 | linear curve (see <a class="citerefentry" href="gluPwlCurve.xml"><span class="citerefentry"><span class="refentrytitle">gluPwlCurve</span></span></a>) or as a single NURBS | |
| 27 | curve (see <a class="citerefentry" href="gluNurbsCurve.xml"><span class="citerefentry"><span class="refentrytitle">gluNurbsCurve</span></span></a>), or as a combination of | |
| 28 | both in any order. The only library calls that can | |
| 29 | appear in a trimming loop definition (between the calls | |
| 30 | to <code class="function">gluBeginTrim</code> and <a class="citerefentry" href="gluEndTrim.xml"><span class="citerefentry"><span class="refentrytitle">gluEndTrim</span></span></a>) are | |
| 31 | <a class="citerefentry" href="gluPwlCurve.xml"><span class="citerefentry"><span class="refentrytitle">gluPwlCurve</span></span></a> and <a class="citerefentry" href="gluNurbsCurve.xml"><span class="citerefentry"><span class="refentrytitle">gluNurbsCurve</span></span></a>. | |
| 32 | </p><p> | |
| 33 | The area of the NURBS surface that is displayed is the | |
| 34 | region in the domain to the left of the trimming curve | |
| 35 | as the curve parameter increases. Thus, the retained | |
| 36 | region of the NURBS surface is inside a | |
| 37 | counterclockwise trimming loop and outside a clockwise | |
| 38 | trimming loop. For the rectangle mentioned earlier, | |
| 39 | the trimming loop for the outer edge of the rectangle runs | |
| 40 | counterclockwise, while the trimming loop for the punched-out hole | |
| 41 | runs clockwise. | |
| 42 | </p><p> | |
| 43 | If you use more than one curve to define a single trimming | |
| 44 | loop, the curve segments must form a closed loop (that is, | |
| 45 | the endpoint of each curve must be the starting point of the | |
| 46 | next curve, and the endpoint of the final curve must | |
| 47 | be the starting point of the first curve). If the | |
| 48 | endpoints of the curve are sufficiently close together | |
| 49 | but not exactly coincident, they will be coerced to match. | |
| 50 | If the endpoints are not sufficiently close, an error results | |
| 51 | (see <a class="citerefentry" href="gluNurbsCallback.xml"><span class="citerefentry"><span class="refentrytitle">gluNurbsCallback</span></span></a>). | |
| 52 | </p><p> | |
| 53 | If a trimming loop definition contains multiple curves, | |
| 54 | the direction of the curves must be consistent (that is, the | |
| 55 | inside must be to the left of all of the curves). Nested | |
| 56 | trimming loops are legal as long as the curve orientations | |
| 57 | alternate correctly. | |
| 58 | If trimming curves are self-intersecting, | |
| 59 | or intersect one another, an error results. | |
| 60 | </p><p> | |
| 61 | If no trimming information is given | |
| 62 | for a NURBS surface, the entire surface is drawn. | |
| 63 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="example"></a><h2>Example</h2><p> | |
| 64 | This code fragment defines a trimming loop that consists of one | |
| 65 | piecewise linear curve, and two NURBS curves: | |
| 66 | </p><pre class="programlisting"> | |
| 67 | gluBeginTrim(nobj); | |
| 68 | gluPwlCurve(..., GLU_MAP1_TRIM_2); | |
| 69 | gluNurbsCurve(..., GLU_MAP1_TRIM_2); | |
| 70 | gluNurbsCurve(..., GLU_MAP1_TRIM_3); | |
| 71 | gluEndTrim(nobj); | |
| 72 | </pre><p> | |
| 73 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p> | |
| 74 | <a class="citerefentry" href="gluBeginSurface.xml"><span class="citerefentry"><span class="refentrytitle">gluBeginSurface</span></span></a>, | |
| 75 | <a class="citerefentry" href="gluNewNurbsRenderer.xml"><span class="citerefentry"><span class="refentrytitle">gluNewNurbsRenderer</span></span></a>, | |
| 76 | <a class="citerefentry" href="gluNurbsCallback.xml"><span class="citerefentry"><span class="refentrytitle">gluNurbsCallback</span></span></a>, | |
| 77 | <a class="citerefentry" href="gluNurbsCurve.xml"><span class="citerefentry"><span class="refentrytitle">gluNurbsCurve</span></span></a>, | |
| 78 | <a class="citerefentry" href="gluPwlCurve.xml"><span class="citerefentry"><span class="refentrytitle">gluPwlCurve</span></span></a> | |
| 79 | </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="Copyright"></a><h2>Copyright</h2><p> | |
| 80 | Copyright <span class="trademark"></span>© 1991-2006 | |
| 81 | Silicon Graphics, Inc. This document is licensed under the SGI | |
| 82 | Free Software B License. For details, see | |
| 83 | <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>. | |
| 84 | </p></div></div></body></html> |