C SPECIFICATION

       void GLAPIENTRY glEvalMesh1( GLenum mode,
                                    GLint i1,
                                    GLint i2 )

PARAMETERS

       mode  In glEvalMesh1, specifies whether to  compute  a  one-dimensional
             mesh of points or lines.  Symbolic constants GL_POINT and GL_LINE
             are accepted.

       i1, i2
             Specify the first and last integer values for grid  domain  vari-
             able i.

C SPECIFICATION

       void GLAPIENTRY glEvalMesh2( GLenum mode,
                                    GLint i1,
                                    GLint i2,
                                    GLint j1,
                                    GLint j2 )

PARAMETERS

       mode   In  glEvalMesh2,  specifies whether to compute a two-dimensional
              mesh  of  points,  lines,  or  polygons.    Symbolic   constants
              GL_POINT, GL_LINE, and GL_FILL are accepted.

       i1, i2 Specify  the first and last integer values for grid domain vari-
              able i.

       j1, j2 Specify the first and last integer values for grid domain  vari-
              able j.

DESCRIPTION

       glMapGrid and glEvalMesh are used in tandem to efficiently generate and
       evaluate a series of evenly-spaced map domain values.  glEvalMesh steps
       through  the  integer  domain  of a one- or two-dimensional grid, whose
       range is the domain of the evaluation  maps  specified  by  glMap1  and
       glMap2.   mode  determines whether the resulting vertices are connected
       as points, lines, or filled polygons.

       In the one-dimensional case, glEvalMesh1, the mesh is generated  as  if
       the following code fragment were executed:


              glBegin( type );
              for ( i = i1; i <= i2; i += 1 )
                 glEvalCoord1( i??u+u1 );
              glEnd();

       ?v=(v2-v1)/m,

where n, u1, u2, m, v1, and v2 are the arguments to the most recent glMapGrid2

command. Then, if mode is GL_FILL, the glEvalMesh2 command is equivalent to:

       for ( j = j1; j < j2; j += 1 ) {
          glBegin( GL_QUAD_STRIP );
          for ( i = i1; i <= i2; i += 1 ) {
             glEvalCoord2( i??u+u1, j??v+v1 );
             glEvalCoord2( i??u+u1, (j+1)??v+v1 );
          }
          glEnd();
       }

If mode is GL_LINE, then a call to glEvalMesh2 is equivalent to:

       for ( j = j1; j <= j2; j += 1 ) {
          glBegin( GL_LINE_STRIP );
          for ( i = i1; i <= i2; i += 1 )
             glEvalCoord2( i??u+u1, j??v+v1 );
          glEnd();
       }

       for ( i = i1;  i <= i2; i += 1 ) {
          glBegin( GL_LINE_STRIP );
          for ( j = j1; j <= j1; j += 1 )
             glEvalCoord2( i??u+u1, j??v+v1 );
          glEnd();
       }

And finally, if mode is GL_POINT, then a call to glEvalMesh2 is equivalent to:

       glBegin( GL_POINTS );
       for ( j = j1; j <= j2; j += 1 )
          for ( i = i1; i <= i2; i += 1 )
             glEvalCoord2( i??u+u1, j??v+v1 );
       glEnd();

In  all  three  cases, the only absolute numeric requirements are that if i=n,
then the value computed from i??u+u1 is exactly u2, and if j=m, then the value
computed from j??v+v1 is exactly v2.

ERRORS

       GL_INVALID_ENUM is generated if mode is not an accepted value.

       GL_INVALID_OPERATION is generated if glEvalMesh is executed between the
       execution of glBegin and the corresponding execution of glEnd.