1GLMAP1(3G) GLMAP1(3G)
2
6 glMap1d, glMap1f - define a one-dimensional evaluator
7
10 void glMap1d( GLenum target,
11 GLdouble u1,
12 GLdouble u2,
13 GLint stride,
14 GLint order,
15 const GLdouble *points )
16 void glMap1f( GLenum target,
17 GLfloat u1,
18 GLfloat u2,
19 GLint stride,
20 GLint order,
21 const GLfloat *points )
22
25 target Specifies the kind of values that are generated by the evalua‐
26 tor. Symbolic constants GL_MAP1_VERTEX_3, GL_MAP1_VERTEX_4,
27 GL_MAP1_INDEX, GL_MAP1_COLOR_4, GL_MAP1_NORMAL,
28 GL_MAP1_TEXTURE_COORD_1, GL_MAP1_TEXTURE_COORD_2,
29 GL_MAP1_TEXTURE_COORD_3, and GL_MAP1_TEXTURE_COORD_4 are
30 accepted.
31 u1, u2 Specify a linear mapping of u, as presented to glEvalCoord1, to
33 ^u, the variable that is evaluated by the equations specified by
34 this command.
35 stride Specifies the number of floats or doubles between the beginning
37 of one control point and the beginning of the next one in the
38 data structure referenced in points. This allows control
39 points to be embedded in arbitrary data structures. The only
40 constraint is that the values for a particular control point
41 must occupy contiguous memory locations.
42 order Specifies the number of control points. Must be positive.
44 points Specifies a pointer to the array of control points.
46
49 Evaluators provide a way to use polynomial or rational polynomial map‐
50 ping to produce vertices, normals, texture coordinates, and colors.
51 The values produced by an evaluator are sent to further stages of GL
52 processing just as if they had been presented using glVertex, glNormal,
53 glTexCoord, and glColor commands, except that the generated values do
54 not update the current normal, texture coordinates, or color.
55 All polynomial or rational polynomial splines of any degree (up to the
57 maximum degree supported by the GL implementation) can be described
58 using evaluators. These include almost all splines used in computer
59 graphics: B-splines, Bezier curves, Hermite splines, and so on.
60 Evaluators define curves based on Bernstein polynomials. Define p(^u)
62 as
63 p(^u)=in=Σ0Bni(^u)Ri
65 where Ri is a control point and Bni(^u) is the ith Bernstein polynomial
67 of degree n (order = n+1):
68 Bni(^u)=⎛⎝n⎞⎠^ui(1−^u)n−i
70 i
71 Recall that
72 00≡1 and ⎛⎝n⎞⎠≡1
74 0
75 glMap1 is used to define the basis and to specify what kind of values
76 are produced. Once defined, a map can be enabled and disabled by call‐
77 ing glEnable and glDisable with the map name, one of the nine prede‐
78 fined values for target described below. glEvalCoord1 evaluates the
79 one-dimensional maps that are enabled. When
80 glEvalCoord1 presents a value u, the Bernstein functions are evaluated
81 using ^u, where
82 ^u=u_u2_−−_uu_11_
84 target is a symbolic constant that indicates what kind of control
87 points are provided in points, and what output is generated when the
88 map is evaluated. It can assume one of nine predefined values:
89 GL_MAP1_VERTEX_3 Each control point is three floating-point
91 values representing x, y, and z. Internal
92 glVertex3 commands are generated when the map
93 is evaluated.
94 GL_MAP1_VERTEX_4 Each control point is four floating-point val‐
96 ues representing x, y, z, and w. Internal
97 glVertex4 commands are generated when the map
98 is evaluated.
99 GL_MAP1_INDEX Each control point is a single floating-point
101 value representing a color index. Internal
102 glIndex commands are generated when the map is
103 evaluated but the current index is not updated
104 with the value of these glIndex commands.
105 GL_MAP1_COLOR_4 Each control point is four floating-point val‐
107 ues representing red, green, blue, and alpha.
108 Internal glColor4 commands are generated when
109 the map is evaluated but the current color is
110 not updated with the value of these glColor4
111 commands.
112 GL_MAP1_NORMAL Each control point is three floating-point
114 values representing the x, y, and z components
115 of a normal vector. Internal glNormal com‐
116 mands are generated when the map is evaluated
117 but the current normal is not updated with the
118 value of these glNormal commands.
119 GL_MAP1_TEXTURE_COORD_1 Each control point is a single floating-point
121 value representing the s texture coordinate.
122 Internal
123 glTexCoord1 commands are generated when the
124 map is evaluated but the current texture coor‐
125 dinates are not updated with the value of
126 these glTexCoord commands.
127 GL_MAP1_TEXTURE_COORD_2 Each control point is two floating-point val‐
129 ues representing the s and t texture coordi‐
130 nates. Internal
131 glTexCoord2 commands are generated when the
132 map is evaluated but the current texture coor‐
133 dinates are not updated with the value of
134 these glTexCoord commands.
135 GL_MAP1_TEXTURE_COORD_3 Each control point is three floating-point
137 values representing the s, t, and r texture
138 coordinates. Internal glTexCoord3 commands
139 are generated when the map is evaluated but
140 the current texture coordinates are not
141 updated with the value of these glTexCoord
142 commands.
143 GL_MAP1_TEXTURE_COORD_4 Each control point is four floating-point val‐
145 ues representing the s, t, r, and q texture
146 coordinates. Internal
147 glTexCoord4 commands are generated when the
148 map is evaluated but the current texture coor‐
149 dinates are not updated with the value of
150 these glTexCoord commands.
151 stride, order, and points define the array addressing for accessing the
153 control points. points is the location of the first control point,
154 which occupies one, two, three, or four contiguous memory locations,
155 depending on which map is being defined. order is the number of con‐
156 trol points in the array. stride specifies how many float or double
157 locations to advance the internal memory pointer to reach the next con‐
158 trol point.
159
161 As is the case with all GL commands that accept pointers to data, it is
162 as if the contents of points were copied by glMap1 before glMap1
163 returns. Changes to the contents of points have no effect after glMap1
164 is called.
165
167 GL_INVALID_ENUM is generated if target is not an accepted value.
168 GL_INVALID_VALUE is generated if u1 is equal to u2.
170 GL_INVALID_VALUE is generated if stride is less than the number of val‐
172 ues in a control point.
173 GL_INVALID_VALUE is generated if order is less than 1 or greater than
175 the return value of GL_MAX_EVAL_ORDER.
176 GL_INVALID_OPERATION is generated if glMap1 is executed between the
178 execution of glBegin and the corresponding execution of glEnd.
179 When the GL_ARB_multitexture extension is supported,
181 GL_INVALID_OPERATION is generated if glMap1 is called and the value of
182 GL_ACTIVE_TEXTURE_ARB is not GL_TEXTURE0_ARB.
183
185 glGetMap
186 glGet with argument GL_MAX_EVAL_ORDER
187 glIsEnabled with argument GL_MAP1_VERTEX_3
188 glIsEnabled with argument GL_MAP1_VERTEX_4
189 glIsEnabled with argument GL_MAP1_INDEX
190 glIsEnabled with argument GL_MAP1_COLOR_4
191 glIsEnabled with argument GL_MAP1_NORMAL
192 glIsEnabled with argument GL_MAP1_TEXTURE_COORD_1
193 glIsEnabled with argument GL_MAP1_TEXTURE_COORD_2
194 glIsEnabled with argument GL_MAP1_TEXTURE_COORD_3
195 glIsEnabled with argument GL_MAP1_TEXTURE_COORD_4
196
198 glBegin(3G), glColor(3G), glEnable(3G), glEvalCoord(3G),
199 glEvalMesh(3G), glEvalPoint(3G), glMap2(3G), glMapGrid(3G),
200 glNormal(3G), glTexCoord(3G), glVertex(3G)
201 GLMAP1(3G)