1GLMAP2(3G)                       OpenGL Manual                      GLMAP2(3G)
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NAME

6       glMap2 - define a two-dimensional evaluator
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C SPECIFICATION

9       void glMap2f(GLenum target, GLfloat u1, GLfloat u2, GLint ustride,
10                    GLint uorder, GLfloat v1, GLfloat v2, GLint vstride,
11                    GLint vorder, const GLfloat * points);
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13       void glMap2d(GLenum target, GLdouble u1, GLdouble u2, GLint ustride,
14                    GLint uorder, GLdouble v1, GLdouble v2, GLint vstride,
15                    GLint vorder, const GLdouble * points);
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PARAMETERS

18       target
19           Specifies the kind of values that are generated by the evaluator.
20           Symbolic constants GL_MAP2_VERTEX_3, GL_MAP2_VERTEX_4,
21           GL_MAP2_INDEX, GL_MAP2_COLOR_4, GL_MAP2_NORMAL,
22           GL_MAP2_TEXTURE_COORD_1, GL_MAP2_TEXTURE_COORD_2,
23           GL_MAP2_TEXTURE_COORD_3, and GL_MAP2_TEXTURE_COORD_4 are accepted.
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25       u1, u2
26           Specify a linear mapping of u, as presented to glEvalCoord2(), to
27           u^, one of the two variables that are evaluated by the equations
28           specified by this command. Initially, u1 is 0 and u2 is 1.
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30       ustride
31           Specifies the number of floats or doubles between the beginning of
32           control point R ij and the beginning of control point R i + 1 ⁢ j,
33           where i and j are the u and v control point indices, respectively.
34           This allows control points to be embedded in arbitrary data
35           structures. The only constraint is that the values for a particular
36           control point must occupy contiguous memory locations. The initial
37           value of ustride is 0.
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39       uorder
40           Specifies the dimension of the control point array in the u axis.
41           Must be positive. The initial value is 1.
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43       v1, v2
44           Specify a linear mapping of v, as presented to glEvalCoord2(), to
45           v^, one of the two variables that are evaluated by the equations
46           specified by this command. Initially, v1 is 0 and v2 is 1.
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48       vstride
49           Specifies the number of floats or doubles between the beginning of
50           control point R ij and the beginning of control point R i ⁡ j + 1,
51           where i and j are the u and v control point indices, respectively.
52           This allows control points to be embedded in arbitrary data
53           structures. The only constraint is that the values for a particular
54           control point must occupy contiguous memory locations. The initial
55           value of vstride is 0.
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57       vorder
58           Specifies the dimension of the control point array in the v axis.
59           Must be positive. The initial value is 1.
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61       points
62           Specifies a pointer to the array of control points.
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DESCRIPTION

65       Evaluators provide a way to use polynomial or rational polynomial
66       mapping to produce vertices, normals, texture coordinates, and colors.
67       The values produced by an evaluator are sent on to further stages of GL
68       processing just as if they had been presented using glVertex(),
69       glNormal(), glTexCoord(), and glColor() commands, except that the
70       generated values do not update the current normal, texture coordinates,
71       or color.
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73       All polynomial or rational polynomial splines of any degree (up to the
74       maximum degree supported by the GL implementation) can be described
75       using evaluators. These include almost all surfaces used in computer
76       graphics, including B-spline surfaces, NURBS surfaces, Bezier surfaces,
77       and so on.
78
79       Evaluators define surfaces based on bivariate Bernstein polynomials.
80       Define p ⁡ u^ v^ as
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82       p ⁡ u^ v^ = Σ i = 0 n Σ j = 0 m B i n ⁡ u^ ⁢ B j m ⁡ v^ ⁢ R ij
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84       where R ij is a control point, B i n ⁡ u^ is the ith Bernstein
85       polynomial of degree n (uorder = n + 1)
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87       B i n ⁡ u^ = n i ⁢ u^ i ⁢ 1 - u^ n - i
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89       and B j m ⁡ v^ is the jth Bernstein polynomial of degree m (vorder = m
90       + 1)
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92       B j m ⁡ v^ = m j ⁢ v^ j ⁢ 1 - v^ m - j
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94       Recall that 0 0 == 1 and n 0 == 1
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96       glMap2 is used to define the basis and to specify what kind of values
97       are produced. Once defined, a map can be enabled and disabled by
98       calling glEnable() and glDisable() with the map name, one of the nine
99       predefined values for target, described below. When glEvalCoord2()
100       presents values u and v, the bivariate Bernstein polynomials are
101       evaluated using u^ and v^, where
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103       u^ = u - u1 u2 - u1
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105       v^ = v - v1 v2 - v1
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107       target is a symbolic constant that indicates what kind of control
108       points are provided in points, and what output is generated when the
109       map is evaluated. It can assume one of nine predefined values:
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111       GL_MAP2_VERTEX_3
112           Each control point is three floating-point values representing x,
113           y, and z. Internal glVertex3() commands are generated when the map
114           is evaluated.
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116       GL_MAP2_VERTEX_4
117           Each control point is four floating-point values representing x, y,
118           z, and w. Internal glVertex4() commands are generated when the map
119           is evaluated.
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121       GL_MAP2_INDEX
122           Each control point is a single floating-point value representing a
123           color index. Internal glIndex() commands are generated when the map
124           is evaluated but the current index is not updated with the value of
125           these glIndex() commands.
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127       GL_MAP2_COLOR_4
128           Each control point is four floating-point values representing red,
129           green, blue, and alpha. Internal glColor4() commands are generated
130           when the map is evaluated but the current color is not updated with
131           the value of these glColor4() commands.
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133       GL_MAP2_NORMAL
134           Each control point is three floating-point values representing the
135           x, y, and z components of a normal vector. Internal glNormal()
136           commands are generated when the map is evaluated but the current
137           normal is not updated with the value of these glNormal() commands.
138
139       GL_MAP2_TEXTURE_COORD_1
140           Each control point is a single floating-point value representing
141           the s texture coordinate. Internal glTexCoord1() commands are
142           generated when the map is evaluated but the current texture
143           coordinates are not updated with the value of these glTexCoord()
144           commands.
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146       GL_MAP2_TEXTURE_COORD_2
147           Each control point is two floating-point values representing the s
148           and t texture coordinates. Internal glTexCoord2() commands are
149           generated when the map is evaluated but the current texture
150           coordinates are not updated with the value of these glTexCoord()
151           commands.
152
153       GL_MAP2_TEXTURE_COORD_3
154           Each control point is three floating-point values representing the
155           s, t, and r texture coordinates. Internal glTexCoord3() commands
156           are generated when the map is evaluated but the current texture
157           coordinates are not updated with the value of these glTexCoord()
158           commands.
159
160       GL_MAP2_TEXTURE_COORD_4
161           Each control point is four floating-point values representing the
162           s, t, r, and q texture coordinates. Internal glTexCoord4() commands
163           are generated when the map is evaluated but the current texture
164           coordinates are not updated with the value of these glTexCoord()
165           commands.
166
167       ustride, uorder, vstride, vorder, and points define the array
168       addressing for accessing the control points.  points is the location of
169       the first control point, which occupies one, two, three, or four
170       contiguous memory locations, depending on which map is being defined.
171       There are uorder × vorder control points in the array.  ustride
172       specifies how many float or double locations are skipped to advance the
173       internal memory pointer from control point R i ⁢ j to control point R i
174       + 1 ⁢ j.  vstride specifies how many float or double locations are
175       skipped to advance the internal memory pointer from control point R i ⁢
176       j to control point R i ⁡ j + 1.
177

NOTES

179       As is the case with all GL commands that accept pointers to data, it is
180       as if the contents of points were copied by glMap2 before glMap2
181       returns. Changes to the contents of points have no effect after glMap2
182       is called.
183
184       Initially, GL_AUTO_NORMAL is enabled. If GL_AUTO_NORMAL is enabled,
185       normal vectors are generated when either GL_MAP2_VERTEX_3 or
186       GL_MAP2_VERTEX_4 is used to generate vertices.
187

ERRORS

189       GL_INVALID_ENUM is generated if target is not an accepted value.
190
191       GL_INVALID_VALUE is generated if u1 is equal to u2, or if v1 is equal
192       to v2.
193
194       GL_INVALID_VALUE is generated if either ustride or vstride is less than
195       the number of values in a control point.
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197       GL_INVALID_VALUE is generated if either uorder or vorder is less than 1
198       or greater than the return value of GL_MAX_EVAL_ORDER.
199
200       GL_INVALID_OPERATION is generated if glMap2 is executed between the
201       execution of glBegin() and the corresponding execution of glEnd().
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203       GL_INVALID_OPERATION is generated if glMap2 is called and the value of
204       GL_ACTIVE_TEXTURE is not GL_TEXTURE0.
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ASSOCIATED GETS

207       glGetMap()
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209       glGet() with argument GL_MAX_EVAL_ORDER
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211       glIsEnabled() with argument GL_MAP2_VERTEX_3
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213       glIsEnabled() with argument GL_MAP2_VERTEX_4
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215       glIsEnabled() with argument GL_MAP2_INDEX
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217       glIsEnabled() with argument GL_MAP2_COLOR_4
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219       glIsEnabled() with argument GL_MAP2_NORMAL
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221       glIsEnabled() with argument GL_MAP2_TEXTURE_COORD_1
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223       glIsEnabled() with argument GL_MAP2_TEXTURE_COORD_2
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225       glIsEnabled() with argument GL_MAP2_TEXTURE_COORD_3
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227       glIsEnabled() with argument GL_MAP2_TEXTURE_COORD_4
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SEE ALSO

230       glBegin(), glColor(), glEnable(), glEvalCoord(), glEvalMesh(),
231       glEvalPoint(), glMap1(), glMapGrid(), glNormal(), glTexCoord(),
232       glVertex()
233
235       Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
236       under the SGI Free Software B License. For details, see
237       http://oss.sgi.com/projects/FreeB/.
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AUTHORS

240       opengl.org
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244opengl.org                        07/13/2018                        GLMAP2(3G)
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