1 <?xml version=
"1.0" encoding=
"UTF-8"?>
2 <!DOCTYPE book PUBLIC
"-//OASIS//DTD DocBook MathML Module V1.1b1//EN"
3 "http://www.oasis-open.org/docbook/xml/mathml/1.1CR1/dbmathml.dtd">
4 <refentry id=
"glEvalPoint">
9 <holder>Silicon Graphics, Inc.
</holder>
12 <refentrytitle>glEvalPoint
</refentrytitle>
13 <manvolnum>3G
</manvolnum>
16 <refname>glEvalPoint
</refname>
17 <refpurpose>generate and evaluate a single point in a mesh
</refpurpose>
19 <refsynopsisdiv><title>C Specification
</title>
22 <funcdef>void
<function>glEvalPoint1
</function></funcdef>
23 <paramdef>GLint
<parameter>i
</parameter></paramdef>
28 <funcdef>void
<function>glEvalPoint2
</function></funcdef>
29 <paramdef>GLint
<parameter>i
</parameter></paramdef>
30 <paramdef>GLint
<parameter>j
</parameter></paramdef>
34 <!-- eqn: ignoring delim $$ -->
35 <refsect1 id=
"parameters"><title>Parameters
</title>
38 <term><parameter>i
</parameter></term>
41 Specifies the integer value for grid domain variable
42 <inlineequation><mml:math><mml:mi mathvariant=
"italic">i
</mml:mi></mml:math></inlineequation>.
47 <term><parameter>j
</parameter></term>
50 Specifies the integer value for grid domain variable
51 <inlineequation><mml:math><mml:mi mathvariant=
"italic">j
</mml:mi></mml:math></inlineequation>
52 (
<function>glEvalPoint2
</function> only).
58 <refsect1 id=
"description"><title>Description
</title>
60 <citerefentry><refentrytitle>glMapGrid
</refentrytitle></citerefentry> and
<citerefentry><refentrytitle>glEvalMesh
</refentrytitle></citerefentry> are used in tandem to efficiently
61 generate and evaluate a series of evenly spaced map domain values.
62 <function>glEvalPoint
</function> can be used to evaluate a single grid point in the same gridspace
63 that is traversed by
<citerefentry><refentrytitle>glEvalMesh
</refentrytitle></citerefentry>.
64 Calling
<function>glEvalPoint1
</function> is equivalent to calling
66 glEvalCoord1(
<mml:math>
67 <!-- eqn: i \cdot DELTA u + u sub 1 :-->
71 <mml:mo>·</mml:mo>
72 <mml:mo>Δ</mml:mo>
73 <mml:mi mathvariant=
"italic">u
</mml:mi>
77 <mml:mi mathvariant=
"italic">u
</mml:mi>
84 <informalequation><mml:math>
85 <!-- eqn: DELTA u = ( u sub 2 - u sub 1 ) / n:-->
88 <mml:mo>Δ</mml:mo>
89 <mml:mi mathvariant=
"italic">u
</mml:mi>
93 <mml:mfenced open=
"(" close=
")">
95 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
99 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
104 <mml:mi mathvariant=
"italic">n
</mml:mi>
107 </mml:math></informalequation>
111 <inlineequation><mml:math><mml:mi mathvariant=
"italic">n
</mml:mi></mml:math></inlineequation>,
112 <inlineequation><mml:math>
113 <!-- eqn: u sub 1:-->
114 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
117 </mml:math></inlineequation>,
119 <inlineequation><mml:math>
120 <!-- eqn: u sub 2:-->
121 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
124 </mml:math></inlineequation>
125 are the arguments to the most recent
<citerefentry><refentrytitle>glMapGrid1
</refentrytitle></citerefentry> command.
126 The one absolute numeric requirement is that if
127 <inlineequation><mml:math>
130 <mml:mi mathvariant=
"italic">i
</mml:mi>
132 <mml:mi mathvariant=
"italic">n
</mml:mi>
134 </mml:math></inlineequation>,
135 then the value computed from
136 <inlineequation><mml:math>
137 <!-- eqn: i cdot DELTA u + u sub 1:-->
140 <mml:mi mathvariant=
"italic">i
</mml:mi>
141 <mml:mo>·</mml:mo>
143 <mml:mo>Δ</mml:mo>
144 <mml:mi mathvariant=
"italic">u
</mml:mi>
148 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
152 </mml:math></inlineequation>
154 <inlineequation><mml:math>
155 <!-- eqn: u sub 2:-->
156 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
159 </mml:math></inlineequation>.
162 In the two-dimensional case,
<function>glEvalPoint2
</function>, let
165 <informalequation><mml:math>
166 <!-- eqn: DELTA u = ( u sub 2 - u sub 1 ) / n:-->
169 <mml:mo>Δ</mml:mo>
170 <mml:mi mathvariant=
"italic">u
</mml:mi>
174 <mml:mfenced open=
"(" close=
")">
176 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
180 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
185 <mml:mi mathvariant=
"italic">n
</mml:mi>
188 </mml:math></informalequation>
190 <informalequation><mml:math>
191 <!-- eqn: DELTA v = ( v sub 2 - v sub 1 ) / m:-->
194 <mml:mo>Δ</mml:mo>
195 <mml:mi mathvariant=
"italic">v
</mml:mi>
199 <mml:mfenced open=
"(" close=
")">
201 <mml:msub><mml:mi mathvariant=
"italic">v
</mml:mi>
205 <mml:msub><mml:mi mathvariant=
"italic">v
</mml:mi>
210 <mml:mi mathvariant=
"italic">m
</mml:mi>
213 </mml:math></informalequation>
218 <inlineequation><mml:math><mml:mi mathvariant=
"italic">n
</mml:mi></mml:math></inlineequation>,
219 <inlineequation><mml:math>
220 <!-- eqn: u sub 1:-->
221 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
224 </mml:math></inlineequation>,
225 <inlineequation><mml:math>
226 <!-- eqn: u sub 2:-->
227 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
230 </mml:math></inlineequation>,
231 <inlineequation><mml:math><mml:mi mathvariant=
"italic">m
</mml:mi></mml:math></inlineequation>,
232 <inlineequation><mml:math>
233 <!-- eqn: v sub 1:-->
234 <mml:msub><mml:mi mathvariant=
"italic">v
</mml:mi>
237 </mml:math></inlineequation>,
239 <inlineequation><mml:math>
240 <!-- eqn: v sub 2:-->
241 <mml:msub><mml:mi mathvariant=
"italic">v
</mml:mi>
244 </mml:math></inlineequation>
245 are the arguments to the most recent
<citerefentry><refentrytitle>glMapGrid2
</refentrytitle></citerefentry> command.
246 Then the
<function>glEvalPoint2
</function> command is equivalent to calling
248 glEvalCoord2(
<mml:math>
249 <!-- i \cdot DELTA u + u sub 1 :-->
253 <mml:mo>·</mml:mo>
254 <mml:mo>Δ</mml:mo>
255 <mml:mi mathvariant=
"italic">u
</mml:mi>
259 <mml:mi mathvariant=
"italic">u
</mml:mi>
263 <!-- j \cdot DELTA v + v sub 1 :-->
266 <mml:mo>·</mml:mo>
267 <mml:mo>Δ</mml:mo>
268 <mml:mi mathvariant=
"italic">v
</mml:mi>
273 <mml:mi mathvariant=
"italic">v
</mml:mi>
279 The only absolute numeric requirements are that if
280 <inlineequation><mml:math>
283 <mml:mi mathvariant=
"italic">i
</mml:mi>
285 <mml:mi mathvariant=
"italic">n
</mml:mi>
287 </mml:math></inlineequation>,
288 then the value computed from
289 <inlineequation><mml:math>
290 <!-- eqn: i cdot DELTA u + u sub 1:-->
293 <mml:mi mathvariant=
"italic">i
</mml:mi>
294 <mml:mo>·</mml:mo>
296 <mml:mo>Δ</mml:mo>
297 <mml:mi mathvariant=
"italic">u
</mml:mi>
301 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
305 </mml:math></inlineequation>
307 <inlineequation><mml:math>
308 <!-- eqn: u sub 2:-->
309 <mml:msub><mml:mi mathvariant=
"italic">u
</mml:mi>
312 </mml:math></inlineequation>,
314 <inlineequation><mml:math>
317 <mml:mi mathvariant=
"italic">j
</mml:mi>
319 <mml:mi mathvariant=
"italic">m
</mml:mi>
321 </mml:math></inlineequation>,
322 then the value computed from
323 <inlineequation><mml:math>
324 <!-- eqn: j cdot DELTA v + v sub 1:-->
327 <mml:mi mathvariant=
"italic">j
</mml:mi>
328 <mml:mo>·</mml:mo>
330 <mml:mo>Δ</mml:mo>
331 <mml:mi mathvariant=
"italic">v
</mml:mi>
335 <mml:msub><mml:mi mathvariant=
"italic">v
</mml:mi>
339 </mml:math></inlineequation>
341 <inlineequation><mml:math>
342 <!-- eqn: v sub 2:-->
343 <mml:msub><mml:mi mathvariant=
"italic">v
</mml:mi>
346 </mml:math></inlineequation>.
349 <refsect1 id=
"associatedgets"><title>Associated Gets
</title>
351 <citerefentry><refentrytitle>glGet
</refentrytitle></citerefentry> with argument
<constant>GL_MAP1_GRID_DOMAIN
</constant>
354 <citerefentry><refentrytitle>glGet
</refentrytitle></citerefentry> with argument
<constant>GL_MAP2_GRID_DOMAIN
</constant>
357 <citerefentry><refentrytitle>glGet
</refentrytitle></citerefentry> with argument
<constant>GL_MAP1_GRID_SEGMENTS
</constant>
360 <citerefentry><refentrytitle>glGet
</refentrytitle></citerefentry> with argument
<constant>GL_MAP2_GRID_SEGMENTS
</constant>
363 <refsect1 id=
"seealso"><title>See Also
</title>
365 <citerefentry><refentrytitle>glEvalCoord
</refentrytitle></citerefentry>,
366 <citerefentry><refentrytitle>glEvalMesh
</refentrytitle></citerefentry>,
367 <citerefentry><refentrytitle>glMap1
</refentrytitle></citerefentry>,
368 <citerefentry><refentrytitle>glMap2
</refentrytitle></citerefentry>,
369 <citerefentry><refentrytitle>glMapGrid
</refentrytitle></citerefentry>
372 <refsect1 id=
"Copyright"><title>Copyright
</title>
374 Copyright
<trademark class=
"copyright"></trademark> 1991-
2006
375 Silicon Graphics, Inc. This document is licensed under the SGI
376 Free Software B License. For details, see
377 <ulink url=
"http://oss.sgi.com/projects/FreeB/">http://oss.sgi.com/projects/FreeB/
</ulink>.