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GLEVALCOORD()                                                    GLEVALCOORD()


NAME

       glEvalCoord1d, glEvalCoord1f, glEvalCoord2d, glEvalCoord2f,
       glEvalCoord1dv, glEvalCoord1fv, glEvalCoord2dv, glEvalCoord2fv -
       evaluate enabled one- and two-dimensional maps


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

           Pp   Pp
       m = -- X --
           Pu   Pv

       Then the generated normal n is

       n = (m/)/(|| 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 ALSO

       glBegin, glColor, glEnable, glEvalMesh, glEvalPoint, glIndex, glMap1,
       glMap2, glMapGrid, glNormal, glTexCoord, glVertex

                                                                 GLEVALCOORD()

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