GLEVALCOORD() MachTen Programmer’s Manual GLEVALCOORD()

NAME
glEvalCoord1d, glEvalCoord1f, glEvalCoord2d, glEvalCo-
ord2f, glEvalCoord1dv, glEvalCoord1fv, glEvalCoord2dv,
glEvalCoord2fv - evaluate enabled one- and two-dimensional
maps

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C SPECIFICATION
void glEvalCoord1d( GLdouble u )
void glEvalCoord1f( GLfloat u )
void glEvalCoord2d( GLdouble u,
GLdouble v )
void glEvalCoord2f( GLfloat u,
GLfloat v )

PARAMETERS
u Specifies a value that is the domain coordinate $u$ to
the basis function defined in a previous glMap1 or
glMap2 command.

v Specifies a value that is the domain coordinate $v$ to
the basis function defined in a previous glMap2 com-
mand. This argument is not present in a glEvalCoord1
command.

C SPECIFICATION
void glEvalCoord1dv( const GLdouble *u )
void glEvalCoord1fv( const GLfloat *u )
void glEvalCoord2dv( const GLdouble *u )
void glEvalCoord2fv( const GLfloat *u )

PARAMETERS
u 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 u. glEvalCoord2 does the same for two-
dimensional maps using two domain values, u and v. To
define a map, call glMap1 and glMap2; to enable and dis-
able 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
are not affected by the values generated by the glEvalCo-
ord commands, but only by the most recent glColor, glIn-
dex, glNormal, and glTexCoord commands.

No commands are issued for maps that are not enabled. If
more than one texture evaluation is enabled for a particu-
lar dimension (for example, GL_MAP2_TEXTURE_COORD_1 and
GL_MAP2_TEXTURE_COORD_2), then only the evaluation of the
map that produces the larger number of coordinates (in
this case, GL_MAP2_TEXTURE_COORD_2) is carried out.
GL_MAP1_VERTEX_4 overrides GL_MAP1_VERTEX_3, and
GL_MAP2_VERTEX_4 overrides GL_MAP2_VERTEX_3, in the same
manner. If neither a three- nor a four-component vertex
map is enabled for the specified dimension, the glEvalCo-
ord 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

Pp Pp
m = -- X --
Pu Pv

Then the generated normal $ n $ is

$n = m over ~ over { || m || }$

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, glIn-
dex, glMap1, glMap2, glMapGrid, glNormal, glTexCoord,
glVertex

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