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 variable
             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⋅Δu+u1 );
              glEnd();
       where

              Δu=(u2−u1)/n

       and  n,  u1, and u2 are the arguments to the most recent glMapGrid1 com‐
       mand.  type is GL_POINTS if mode is GL_POINT, or  GL_LINES  if  mode  is

              for ( j = j1; j < j2; j += 1 ) {
                 glBegin( GL_QUAD_STRIP );
                 for ( i = i1; i <= i2; i += 1 ) {
                    glEvalCoord2( i⋅Δu+u1, j⋅Δv+v1 );
                    glEvalCoord2( i⋅Δu+u1, (j+1)⋅Δv+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⋅Δu+u1, j⋅Δv+v1 );
                 glEnd();
              }

              for ( i = i1;  i <= i2; i += 1 ) {
                 glBegin( GL_LINE_STRIP );
                 for ( j = j1; j <= j1; j += 1 )
                    glEvalCoord2( i⋅Δu+u1, j⋅Δv+v1 );
                 glEnd();
              }

       And finally, if mode is GL_POINT, then a call to glEvalMesh2 is  equiva‐
       lent to:

              glBegin( GL_POINTS );
              for ( j = j1; j <= j2; j += 1 )
                 for ( i = i1; i <= i2; i += 1 )
                    glEvalCoord2( i⋅Δu+u1, j⋅Δv+v1 );
              glEnd();

       In  all  three cases, the only absolute numeric requirements are that if
       i=n, then the value computed from i⋅Δu+u1 is exactly  u2,  and  if  j=m,
       then the value computed from j⋅Δv+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.

ASSOCIATED GETS
       glGet with argument GL_MAP1_GRID_DOMAIN
       glGet with argument GL_MAP2_GRID_DOMAIN
       glGet with argument GL_MAP1_GRID_SEGMENTS
       glGet with argument GL_MAP2_GRID_SEGMENTS

SEE ALSO