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GLEVALCOORD(3G)                                                                              GLEVALCOORD(3G)



NAME
       glEvalCoord1d, glEvalCoord1f, glEvalCoord2d, glEvalCoord2f, glEvalCoord1dv, glEvalCoord1fv, glEvalCo-ord2dv, glEvalCoord2dv,
       ord2dv, 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 cur-rent current
       rent values for those evaluations that are enabled, and current values otherwise, However, the evalu-ated evaluated
       ated  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  com-mands commands
       mands  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-com-ponent four-component
       ponent 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

                         m = (partial (p) / partial (u)) X (partial (p) over partial (v))

       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(3G),  glColor(3G),  glEnable(3G),  glEvalMesh(3G), glEvalPoint(3G), glIndex(3G), glMap1(3G), glMap2(3G), glMapGrid(3G), glNormal(3G),
       glTexCoord(3G), glVertex(3G)




                                                                                             GLEVALCOORD(3G)