1GLMAP1(3G) OpenGL Manual GLMAP1(3G)
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6 glMap1 - define a one-dimensional evaluator
7
9 void glMap1f(GLenum target, GLfloat u1, GLfloat u2, GLint stride,
10 GLint order, const GLfloat * points);
11 void glMap1d(GLenum target, GLdouble u1, GLdouble u2, GLint stride,
13 GLint order, const GLdouble * points);
14
16 target
17 Specifies the kind of values that are generated by the evaluator.
18 Symbolic constants GL_MAP1_VERTEX_3, GL_MAP1_VERTEX_4,
19 GL_MAP1_INDEX, GL_MAP1_COLOR_4, GL_MAP1_NORMAL,
20 GL_MAP1_TEXTURE_COORD_1, GL_MAP1_TEXTURE_COORD_2,
21 GL_MAP1_TEXTURE_COORD_3, and GL_MAP1_TEXTURE_COORD_4 are accepted.
22 u1, u2
24 Specify a linear mapping of u, as presented to glEvalCoord1(), to
25 u^, the variable that is evaluated by the equations specified by
26 this command.
27 stride
29 Specifies the number of floats or doubles between the beginning of
30 one control point and the beginning of the next one in the data
31 structure referenced in points. This allows control points to be
32 embedded in arbitrary data structures. The only constraint is that
33 the values for a particular control point must occupy contiguous
34 memory locations.
35 order
37 Specifies the number of control points. Must be positive.
38 points
40 Specifies a pointer to the array of control points.
41
43 Evaluators provide a way to use polynomial or rational polynomial
44 mapping to produce vertices, normals, texture coordinates, and colors.
45 The values produced by an evaluator are sent to further stages of GL
46 processing just as if they had been presented using glVertex(),
47 glNormal(), glTexCoord(), and glColor() commands, except that the
48 generated values do not update the current normal, texture coordinates,
49 or color.
50 All polynomial or rational polynomial splines of any degree (up to the
52 maximum degree supported by the GL implementation) can be described
53 using evaluators. These include almost all splines used in computer
54 graphics: B-splines, Bezier curves, Hermite splines, and so on.
55 Evaluators define curves based on Bernstein polynomials. Define p u^
57 as
58 p u^ = Σ i = 0 n B i n u^ R i
60 where R i is a control point and B i n u^ is the ith Bernstein
62 polynomial of degree n (order = n + 1):
63 B i n u^ = n i u^ i 1 - u^ n - i
65 Recall that
67 0 0 == 1 and n 0 == 1
69 glMap1 is used to define the basis and to specify what kind of values
71 are produced. Once defined, a map can be enabled and disabled by
72 calling glEnable() and glDisable() with the map name, one of the nine
73 predefined values for target described below. glEvalCoord1() evaluates
74 the one-dimensional maps that are enabled. When glEvalCoord1() presents
75 a value u, the Bernstein functions are evaluated using u^, where u^ = u
76 - u1 u2 - u1
77 target is a symbolic constant that indicates what kind of control
79 points are provided in points, and what output is generated when the
80 map is evaluated. It can assume one of nine predefined values:
81 GL_MAP1_VERTEX_3
83 Each control point is three floating-point values representing x,
84 y, and z. Internal glVertex3() commands are generated when the map
85 is evaluated.
86 GL_MAP1_VERTEX_4
88 Each control point is four floating-point values representing x, y,
89 z, and w. Internal glVertex4() commands are generated when the map
90 is evaluated.
91 GL_MAP1_INDEX
93 Each control point is a single floating-point value representing a
94 color index. Internal glIndex() commands are generated when the map
95 is evaluated but the current index is not updated with the value of
96 these glIndex() commands.
97 GL_MAP1_COLOR_4
99 Each control point is four floating-point values representing red,
100 green, blue, and alpha. Internal glColor4() commands are generated
101 when the map is evaluated but the current color is not updated with
102 the value of these glColor4() commands.
103 GL_MAP1_NORMAL
105 Each control point is three floating-point values representing the
106 x, y, and z components of a normal vector. Internal glNormal()
107 commands are generated when the map is evaluated but the current
108 normal is not updated with the value of these glNormal() commands.
109 GL_MAP1_TEXTURE_COORD_1
111 Each control point is a single floating-point value representing
112 the s texture coordinate. Internal glTexCoord1() commands are
113 generated when the map is evaluated but the current texture
114 coordinates are not updated with the value of these glTexCoord()
115 commands.
116 GL_MAP1_TEXTURE_COORD_2
118 Each control point is two floating-point values representing the s
119 and t texture coordinates. Internal glTexCoord2() commands are
120 generated when the map is evaluated but the current texture
121 coordinates are not updated with the value of these glTexCoord()
122 commands.
123 GL_MAP1_TEXTURE_COORD_3
125 Each control point is three floating-point values representing the
126 s, t, and r texture coordinates. Internal glTexCoord3() commands
127 are generated when the map is evaluated but the current texture
128 coordinates are not updated with the value of these glTexCoord()
129 commands.
130 GL_MAP1_TEXTURE_COORD_4
132 Each control point is four floating-point values representing the
133 s, t, r, and q texture coordinates. Internal glTexCoord4() commands
134 are generated when the map is evaluated but the current texture
135 coordinates are not updated with the value of these glTexCoord()
136 commands.
137 stride, order, and points define the array addressing for accessing the
139 control points. points is the location of the first control point,
140 which occupies one, two, three, or four contiguous memory locations,
141 depending on which map is being defined. order is the number of
142 control points in the array. stride specifies how many float or double
143 locations to advance the internal memory pointer to reach the next
144 control point.
145
147 As is the case with all GL commands that accept pointers to data, it is
148 as if the contents of points were copied by glMap1 before glMap1
149 returns. Changes to the contents of points have no effect after glMap1
150 is called.
151
153 GL_INVALID_ENUM is generated if target is not an accepted value.
154 GL_INVALID_VALUE is generated if u1 is equal to u2.
156 GL_INVALID_VALUE is generated if stride is less than the number of
158 values in a control point.
159 GL_INVALID_VALUE is generated if order is less than 1 or greater than
161 the return value of GL_MAX_EVAL_ORDER.
162 GL_INVALID_OPERATION is generated if glMap1 is executed between the
164 execution of glBegin() and the corresponding execution of glEnd().
165 GL_INVALID_OPERATION is generated if glMap1 is called and the value of
167 GL_ACTIVE_TEXTURE is not GL_TEXTURE0.
168
170 glGetMap()
171 glGet() with argument GL_MAX_EVAL_ORDER
173 glIsEnabled() with argument GL_MAP1_VERTEX_3
175 glIsEnabled() with argument GL_MAP1_VERTEX_4
177 glIsEnabled() with argument GL_MAP1_INDEX
179 glIsEnabled() with argument GL_MAP1_COLOR_4
181 glIsEnabled() with argument GL_MAP1_NORMAL
183 glIsEnabled() with argument GL_MAP1_TEXTURE_COORD_1
185 glIsEnabled() with argument GL_MAP1_TEXTURE_COORD_2
187 glIsEnabled() with argument GL_MAP1_TEXTURE_COORD_3
189 glIsEnabled() with argument GL_MAP1_TEXTURE_COORD_4
191
193 glBegin(), glColor(), glEnable(), glEvalCoord(), glEvalMesh(),
194 glEvalPoint(), glMap2(), glMapGrid(), glNormal(), glTexCoord(),
195 glVertex()
196
198 Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
199 under the SGI Free Software B License. For details, see
200 http://oss.sgi.com/projects/FreeB/.
201
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204opengl.org 07/13/2018 GLMAP1(3G)