- evaluate enabled one- and two-dimensional maps
C SPECIFICATION
PARAMETERS
_param1 Specifies a value that is the domain coordinate u
to the basis function defined in a previous
glMap1 or glMap2 command.
_param2 Specifies a value that is the domain coordinate v
to the basis function defined in a previous
glMap2 command. This argument is not present in
a glEvalCoord1 command.
C SPECIFICATION
PARAMETERS
_param1
Specifies a pointer to an array containing either
one or two domain coordinates. The first coordi-
nate is u. The second coordinate is v, which is
present only in glEvalCoord2 versions.
DESCRIPTION
glEvalCoord1 evaluates enabled one-dimensional maps at
argument _param1(1). glEvalCoord2 does the same for two-
dimensional maps using two domain values, _param1(1) and
_param2(1). To define a map, call glMap1 and glMap2; to
enable and disable it, call glEnable and glDisable.
When one of the glEvalCoord commands is issued, all cur-
rently enabled maps of the indicated dimension are evalu-
ated. Then, for each enabled map, it is as if the corre-
sponding GL command had been issued with the computed
value. That is, if GL_MAP1_INDEX or GL_MAP2_INDEX is
enabled, a glIndex command is simulated. If
GL_MAP1_COLOR_4 or GL_MAP2_COLOR_4 is enabled, a glColor
command is simulated. If GL_MAP1_NORMAL or GL_MAP2_NORMAL
is enabled, a normal vector is produced, and if any of
GL_MAP1_TEXTURE_COORD_1, GL_MAP1_TEXTURE_COORD_2,
GL_MAP1_TEXTURE_COORD_3, GL_MAP1_TEXTURE_COORD_4,
GL_MAP2_TEXTURE_COORD_1, GL_MAP2_TEXTURE_COORD_2,
GL_MAP2_TEXTURE_COORD_3, or GL_MAP2_TEXTURE_COORD_4 is
enabled, then an appropriate glTexCoord command is simu-
lated.
For color, color index, normal, and texture coordinates
the GL uses evaluated values instead of current values for
those evaluations that are enabled, and current values
otherwise, However, the evaluated values do not update the
current values. Thus, if glVertex commands are inter-
spersed with glEvalCoord commands, the color, normal, and
texture coordinates associated with the glVertex commands
glEvalCoord command is ignored.
If you have enabled automatic normal generation, by call-
ing glEnable with argument GL_AUTO_NORMAL, glEvalCoord2
generates surface normals analytically, regardless of the
contents or enabling of the GL_MAP2_NORMAL map. Let
m=_<I>u_x_<I>v_
Then the generated normal n is
n=_____
If automatic normal generation is disabled, the corre-
sponding normal map GL_MAP2_NORMAL, if enabled, is used to
produce a normal. If neither automatic normal generation
nor a normal map is enabled, no normal is generated for
glEvalCoord2 commands.
ASSOCIATED GETS
glIsEnabled with argument GL_MAP1_VERTEX_3
glIsEnabled with argument GL_MAP1_VERTEX_4
glIsEnabled with argument GL_MAP1_INDEX
glIsEnabled with argument GL_MAP1_COLOR_4
glIsEnabled with argument GL_MAP1_NORMAL
glIsEnabled with argument GL_MAP1_TEXTURE_COORD_1
glIsEnabled with argument GL_MAP1_TEXTURE_COORD_2
glIsEnabled with argument GL_MAP1_TEXTURE_COORD_3
glIsEnabled with argument GL_MAP1_TEXTURE_COORD_4
glIsEnabled with argument GL_MAP2_VERTEX_3
glIsEnabled with argument GL_MAP2_VERTEX_4
glIsEnabled with argument GL_MAP2_INDEX
glIsEnabled with argument GL_MAP2_COLOR_4
glIsEnabled with argument GL_MAP2_NORMAL
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_1
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_2
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_3
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_4
glIsEnabled with argument GL_AUTO_NORMAL
glGetMap
SEE ALSO
glBegin, glColor, glEnable, glEvalMesh, glEvalPoint,
glIndex, glMap1, glMap2, glMapGrid, glNormal, glTexCoord,
glVertex
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