fglEvalMesh(3G)

NAME
     fglEvalMesh1, fglEvalMesh2 - compute a one- or two-dimensional grid of
     points or lines


FORTRAN SPECIFICATION
     SUBROUTINE fglEvalMesh1( INTEGER*4 mode,
                              INTEGER*4 i1,
                              INTEGER*4 i2 )


PARAMETERS
     mode  In fglEvalMesh1, 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.

FORTRAN SPECIFICATION
     SUBROUTINE fglEvalMesh2( INTEGER*4 mode,
                              INTEGER*4 i1,
                              INTEGER*4 i2,
                              INTEGER*4 j1,
                              INTEGER*4 j2 )


PARAMETERS
     mode In fglEvalMesh2, 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 variable
          i.

     j1, j2
          Specify the first and last integer values for grid domain variable
          j.

DESCRIPTION
     fglMapGrid and fglEvalMesh are used in tandem to efficiently generate and
     evaluate a series of evenly-spaced map domain values.  fglEvalMesh steps
     through the integer domain of a one- or two-dimensional grid, whose range
     is the domain of the evaluation maps specified by fglMap1 and fglMap2.
     mode determines whether the resulting vertices are connected as points,
     lines, or filled polygons.

     In the one-dimensional case, fglEvalMesh1, the mesh is generated as if
     the following code fragment were executed:

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

     where

          Wu = (u  - u )/n
                   2    1


     and n, u , and u  are the arguments to the most recent fglMapGrid1
             1       2
     command.  type is GL_POINTS if mode is GL_POINT, or GL_LINES if mode is
     GL_LINE.

     The one absolute numeric requirement is that if i = n, then the value
                    .
     computed from i Wu + u  is exactly u .
                             1             2

     In the two-dimensional case, fglEvalMesh2, let

          Wu = (u  - u )/n
                   2    1

          Wv = (v  - v )/m,
                   2    1

     where n, u , u , m, v , and v  are the arguments to the most recent
               1   2      1       2
     fglMapGrid2 command.  Then, if mode is GL_FILL, the fglEvalMesh2 command
     is equivalent to:


          for ( j = j1; j < j2; j += 1 ) {
             glBegin( GL_QUAD_STRIP );
             for ( i = i1; i <= i2; i += 1 ) {
                               .            .
                glEvalCoord2( i Wu + u , j Wv + v  );
                                        1            1
                               .                .
                glEvalCoord2( i Wu + u , (j+1) Wv + v  );
                                        1                1
             }
             glEnd();
          }


     If mode is GL_LINE, then a call to fglEvalMesh2 is equivalent to:


          for ( j = j1; j <= j2; j += 1 ) {
             glBegin( GL_LINE_STRIP );
             for ( i = i1; i <= i2; i += 1 )
                               .            .
                glEvalCoord2( i Wu + u , j Wv + v  );
                                        1            1
             glEnd();
          }

          for ( i = i1;  i <= i2; i += 1 ) {
             glBegin( GL_LINE_STRIP );
             for ( j = j1; j <= j1; j += 1 )
                               .            .
                glEvalCoord2( i Wu + u , j Wv + v  );
                                        1            1
             glEnd();
          }


     And finally, if mode is GL_POINT, then a call to fglEvalMesh2 is
     equivalent to:


          glBegin( GL_POINTS );
          for ( j = j1; j <= j2; j += 1 )
             for ( i = i1; i <= i2; i += 1 )
                               .            .
                glEvalCoord2( i Wu + u , j Wv + v  );
                                        1            1
          glEnd();


     In all three cases, the only absolute numeric requirements are that if
                                          .
     i = n, then the value computed from i Wu + u  is exactly u , and if
                                                   1             2
                                          .
     j = m, then the value computed from j Wv + v  is exactly v .
                                                   1             2

ERRORS
     GL_INVALID_ENUM is generated if mode is not an accepted value.

     GL_INVALID_OPERATION is generated if fglEvalMesh is executed between the
     execution of fglBegin and the corresponding execution of fglEnd.

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


MACHINE DEPENDENCIES
     RealityEngine, RealityEngine2, and VTX systems do not handle 1D maps for
     colors correctly.


SEE ALSO
     fglBegin, fglEvalCoord, fglEvalPoint, fglMap1, fglMap2, fglMapGrid