NAME    [Toc]    [Back]

       glEvalCoord,  glEvalCoord1d, glEvalCoord1f, glEvalCoord2d,
       glEvalCoord2f, glEvalCoord1dv,  glEvalCoord1fv,  glEvalCoord2dv,
  glEvalCoord2fv  -  evaluate enabled one- and twodimensional
 maps

SYNOPSIS    [Toc]    [Back]

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

PARAMETERS    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

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

PARAMETERS    [Toc]    [Back]

       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    [Toc]    [Back]

       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
           dp   du m = -- x --
           du   dv


       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    [Toc]    [Back]

       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    [Toc]    [Back]

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



                                                  glEvalCoord(3G)