1GLEVALMESH(3G)                   OpenGL Manual                  GLEVALMESH(3G)
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3
4

NAME

6       glEvalMesh - compute a one- or two-dimensional grid of points or lines
7

C SPECIFICATION

9       void glEvalMesh1(GLenum mode, GLint i1, GLint i2);
10

PARAMETERS

12       mode
13           In glEvalMesh1, specifies whether to compute a one-dimensional mesh
14           of points or lines. Symbolic constants GL_POINT and GL_LINE are
15           accepted.
16
17       i1, i2
18           Specify the first and last integer values for grid domain variable
19           i.
20

C SPECIFICATION

22       void glEvalMesh2(GLenum mode, GLint i1, GLint i2, GLint j1, GLint j2);
23

PARAMETERS

25       mode
26           In glEvalMesh2, specifies whether to compute a two-dimensional mesh
27           of points, lines, or polygons. Symbolic constants GL_POINT,
28           GL_LINE, and GL_FILL are accepted.
29
30       i1, i2
31           Specify the first and last integer values for grid domain variable
32           i.
33
34       j1, j2
35           Specify the first and last integer values for grid domain variable
36           j.
37

DESCRIPTION

39       glMapGrid() and glEvalMesh are used in tandem to efficiently generate
40       and evaluate a series of evenly-spaced map domain values.  glEvalMesh
41       steps through the integer domain of a one- or two-dimensional grid,
42       whose range is the domain of the evaluation maps specified by glMap1()
43       and glMap2().  mode determines whether the resulting vertices are
44       connected as points, lines, or filled polygons.
45
46       In the one-dimensional case, glEvalMesh1, the mesh is generated as if
47       the following code fragment were executed:
48
49           glBegin( type );
50           for ( i = i1; i <= i2; i += 1 )
51              glEvalCoord1(
52
53
54
55                                   i
56
57                                Δ
58                                   u
59
60                               +
61
62                                   u
63                                   1
64
65
66                        );
67           glEnd();
68
69
70       where
71
72       Δ u = u 2 - u 1 n
73
74       and n, u 1, and u 2 are the arguments to the most recent glMapGrid1()
75       command.  type is GL_POINTS if mode is GL_POINT, or GL_LINES if mode is
76       GL_LINE.
77
78       The one absolute numeric requirement is that if i = n, then the value
79       computed from i ⋅ Δ u + u 1 is exactly u 2.
80
81       In the two-dimensional case, glEvalMesh2, let .cp Δ u = u 2 - u 1 n
82
83       Δ v = v 2 - v 1 m
84
85       where n, u 1, u 2, m, v 1, and v 2 are the arguments to the most recent
86       glMapGrid2() command. Then, if mode is GL_FILL, the glEvalMesh2 command
87       is equivalent to:
88
89           for ( j = j1; j < j2; j += 1 ) {
90              glBegin( GL_QUAD_STRIP );
91              for ( i = i1; i <= i2; i += 1 ) {
92                 glEvalCoord2(
93
94
95
96                                  i
97
98                                  Δ
99                                     u
100
101                                 +
102
103                                     u
104                                     1
105
106                              ,
107
108
109                                  j
110
111                                  Δ
112                                     v
113
114
115                                 +
116
117                                     v
118                                     1
119
120
121                          );
122                 glEvalCoord2(
123
124
125
126                                  i
127
128                                  Δ
129                                     u
130
131                                 +
132
133                                     u
134                                     1
135
136                              ,
137
138
139
140
141
142                                              j
143                                           +
144                                              1
145
146
147
148
149                                  Δ
150                                     v
151
152                                 +
153
154                                     v
155                                     1
156
157
158                          );
159              }
160              glEnd();
161           }
162
163
164       If mode is GL_LINE, then a call to glEvalMesh2 is equivalent to:
165
166           for ( j = j1; j <= j2; j += 1 ) {
167              glBegin( GL_LINE_STRIP );
168              for ( i = i1; i <= i2; i += 1 )
169                 glEvalCoord2(
170
171
172
173                                  i
174
175                                  Δ
176                                     u
177
178                                 +
179
180                                     u
181                                     1
182
183                              ,
184
185
186                                  j
187
188                                  Δ
189                                     v
190
191                                 +
192
193                                     v
194                                     1
195
196
197                          );
198              glEnd();
199           }
200
201           for ( i = i1;  i <= i2; i += 1 ) {
202              glBegin( GL_LINE_STRIP );
203              for ( j = j1; j <= j1; j += 1 )
204                 glEvalCoord2(
205
206
207
208                                  i
209
210                                  Δ
211                                     u
212
213                                 +
214
215                                     u
216                                     1
217
218                              ,
219
220
221                                  j
222
223                                  Δ
224                                     v
225
226                                 +
227
228                                     v
229                                     1
230
231
232                          );
233              glEnd();
234           }
235
236
237       And finally, if mode is GL_POINT, then a call to glEvalMesh2 is
238       equivalent to:
239
240           glBegin( GL_POINTS );
241           for ( j = j1; j <= j2; j += 1 )
242              for ( i = i1; i <= i2; i += 1 )
243                 glEvalCoord2(
244
245
246
247                                  i
248
249                                  Δ
250                                     u
251
252                                 +
253
254                                     u
255                                     1
256
257                              ,
258
259
260                                  j
261
262                                  Δ
263                                     v
264
265                                 +
266
267                                     v
268                                     1
269
270
271                          );
272           glEnd();
273
274
275       In all three cases, the only absolute numeric requirements are that if
276       i = n, then the value computed from i ⋅ Δ u + u 1 is exactly u 2, and
277       if j = m, then the value computed from j ⋅ Δ v + v 1 is exactly v 2.
278

ERRORS

280       GL_INVALID_ENUM is generated if mode is not an accepted value.
281
282       GL_INVALID_OPERATION is generated if glEvalMesh is executed between the
283       execution of glBegin() and the corresponding execution of glEnd().
284

ASSOCIATED GETS

286       glGet() with argument GL_MAP1_GRID_DOMAIN
287
288       glGet() with argument GL_MAP2_GRID_DOMAIN
289
290       glGet() with argument GL_MAP1_GRID_SEGMENTS
291
292       glGet() with argument GL_MAP2_GRID_SEGMENTS
293

SEE ALSO

295       glBegin(), glEvalCoord(), glEvalPoint(), glMap1(), glMap2(),
296       glMapGrid()
297
299       Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
300       under the SGI Free Software B License. For details, see
301       http://oss.sgi.com/projects/FreeB/.
302

AUTHORS

304       opengl.org
305
306
307
308opengl.org                        07/13/2018                    GLEVALMESH(3G)
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