GLEVALCOORD(3G)GLEVALCOORD(3G)NAME
glEvalCoord1d, glEvalCoord1f, glEvalCoord2d, glEvalCoord2f,
glEvalCoord1dv, glEvalCoord1fv, glEvalCoord2dv, glEvalCoord2fv -
evaluate enabled one- and two-dimensional maps
delim $$
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 command. 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 coordinate 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 disable it, call glEnable and glDisable.
When one of the glEvalCoord commands is issued, all currently enabled
maps of the indicated dimension are evaluated. Then, for each enabled
map, it is as if the corresponding 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 simulated.
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 interspersed with glEvalCoord commands, the color, normal, and
texture coordinates associated with the glVertex commands are not
affected by the values generated by the glEvalCoord commands, but only
by the most recent glColor, glIndex, glNormal, and glTexCoord commands.
No commands are issued for maps that are not enabled. If more than one
texture evaluation is enabled for a particular 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 glEvalCoord command is ignored.
If you have enabled automatic normal generation, by calling glEnable
with argument GL_AUTO_NORMAL, glEvalCoord2 generates surface normals
analytically, regardless of the contents or enabling of the
GL_MAP2_NORMAL map. Let
bold m ~=~ {partial bold p} over {partial u} ~times~
{partial bold p} over {partial v}
Then the generated normal $ bold n $ is
$bold n ~=~ bold m over { || bold m || }$
If automatic normal generation is disabled, the corresponding 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 ALSOglBegin(3G),
glColor(3G),
glEnable(3G),
glEvalMesh(3G),
glEvalPoint(3G),
glIndex(3G),
glMap1(3G),
glMap2(3G),
glMapGrid(3G),
glNormal(3G),
glTexCoord(3G),
glVertex(3G)
March 1, 2011
