GLEVALMESH(3G)                                                  GLEVALMESH(3G)



NAME
       glEvalesh1,,  glEvalesh2  -  compute a one- or two-dimensional grid of
       points or lines


C SPECIFICATION
       void glEvalesh1( GLenum mode,
                         GLint i1,
                         GLint i2 )


PARAMETERS
       mode  In glEvalesh1, specifies whether to  compute  a  one-dimensional
             mesh of points or lines.  Symbolic constants GLPOINT and GLINE
             are accepted.

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

C SPECIFICATION
       void glEvalesh2( GLenum mode,
                         GLint i1,
                         GLint i2,
                         GLint j1,
                         GLint j2 )


PARAMETERS
       mode   In  glEvalesh2,  specifies whether to compute a two-dimensional
              mesh  of  points,  lines,  or  polygons.    Symbolic   constants
              GLPOINT, GLINE, and GLFIL 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
       glapGrid and glEvalesh are used in tandem to efficiently generate and
       evaluate a series of evenly-spaced map domain values.  glEvalesh steps
       through  the  integer  domain  of a one- or two-dimensional grid, whose
       range is the domain of the evaluation  maps  specified  by  glap1  and
       glap2.   mode  determines whether the resulting vertices are connected
       as points, lines, or filled polygons.

       In the one-dimensional case, glEvalesh1, the mesh is generated  as  if
       the following code fragment were executed:

              glBegin( type );
              for ( i = i1; i <= i2; i ]= 1 )
                 glEvalCoord1( i dot DELTA u ] u1 );
              glEnd();
where

              DELTA(u) = (u2 - u1 ) / n


and  n,  u1,  and  u2 are the arguments to the most recent glapGrid1 command.
type is GLPOINTS if mode is GLPOINT, or GLINES if mode is GLINE.

The one absolute numeric requirement is that if i = n, then the value computed
from i dot DELTA(u) ] u1 is exactly u2.

In the two-dimensional case, glEvalesh2, let

       DELTA(u) = ( u2 - u1 ) / n

       DELTA(v) = ( v2 - v1 ) / m,

where n, u1, u2, m, v1, and v2 are the arguments to the most recent glapGrid2
command.  Then, if mode is GLFIL, the glEvalesh2 command is equivalent to:

       for ( j = j1; j < j2; j ]= 1 ) {
          glBegin( GLQUADSTRIP );
          for ( i = i1; i <= i2; i ]= 1 ) {
             glEvalCoord2( i dot DELTA(u) ] u1, j dot DELTA(v) ] v1 );
             glEvalCoord2( i dot DELTA(u) ] u1, (j]1) dot DELTA(v) ] v1 );
          }
          glEnd();
       }

If mode is GLINE, then a call to glEvalesh2 is equivalent to:

       for ( j = j1; j <= j2; j ]= 1 ) {
          glBegin( GLINESTRIP );
          for ( i = i1; i <= i2; i ]= 1 )
             glEvalCoord2( i dot DELTA(u) ] u1, j dot DELTA(v) ] v1 );
          glEnd();
       }

       for ( i = i1;  i <= i2; i ]= 1 ) {
          glBegin( GLINESTRIP );
          for ( j = j1; j <= j1; j ]= 1 )
             glEvalCoord2( i dot DELTA(u) ] u1, j dot v ] v1 );
          glEnd();
       }

And finally, if mode is GLPOINT, then a call to glEvalesh2 is equivalent to:

       glBegin( GLPOINTS );
       for ( j = j1; j <= j2; j ]= 1 )
          for ( i = i1; i <= i2; i ]= 1 )
             glEvalCoord2( i dot u ] u1, j dot DELTA(v) ] v1 );
       glEnd();

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

ERORS
       GLINVALIDENUM is generated if mode is not an accepted value.

       GLINVALIDOPERATION is generated if glEvalesh is executed between the
       execution of glBegin and the corresponding execution of glEnd.

ASOCIATED GETS
       glGet with argument GLMAP1GRIDOMAIN
       glGet with argument GLMAP2GRIDOMAIN
       glGet with argument GLMAP1GRIDSEGMENTS
       glGet with argument GLMAP2GRIDSEGMENTS

SEE ALSO
       glBegin, glEvalCoord, glEvalPoint, glap1, glap2, glapGrid



                                                                GLEVALMESH(3G)