glEvalPoint1(3)

NAME

       glEvalPoint1,  glEvalPoint2 - generate and evaluate a single point in a
       mesh

C SPECIFICATION

       void glEvalPoint1( GLint i )
       void glEvalPoint2( GLint i,
                          GLint j )

       delim $$

PARAMETERS

       i  Specifies the integer value for grid domain variable $i$.

       j  Specifies  the  integer  value  for  grid  domain  variable  $j$  (-
          glEvalPoint2 only).

DESCRIPTION

       glMapGrid and glEvalMesh are used in tandem to efficiently generate and
       evaluate a series of evenly spaced map domain values.  glEvalPoint  can
       be  used  to evaluate a single grid point in the same gridspace that is
       traversed by glEvalMesh.  Calling glEvalPoint1 is equivalent to calling

              glEvalCoord1( i$^cdot^DELTA u ~+~ u sub 1$ );

where

              $DELTA u ~=~ ( u sub 2 - u sub 1 ) ^/^ n$

and  $n$,  $u  sub  1$,  and  $u  sub  2$ are the arguments to the most recent

glMapGrid1 command. The one absolute numeric requirement is that if $i~=~n$,

then  the value computed from $i ^cdot^ DELTA u ~+~ u sub 1$ is exactly $u sub
2$.

In the two-dimensional case, glEvalPoint2, let

       $DELTA u ~=~ mark ( u sub 2 - u sub 1 ) ^/^ n$

       $DELTA v ~=~ mark ( v sub 2 - v sub 1 ) ^/^ m,$

where $n$, $u sub 1$, $u sub 2$, $m$, $v sub 1$, and $v sub 2$ are  the  argu-

ments to the most recent glMapGrid2 command. Then the glEvalPoint2 command is

equivalent to calling

       glEvalCoord2( i$^cdot^DELTA u ~+~ u sub 1$, j$^cdot^DELTA v ~+~ v sub 1$ );

The only absolute numeric requirements are that if  $i~=~n$,  then  the  value
computed  from  $i  ^cdot^DELTA  u  ~+~  u sub 1$ is exactly $u sub 2$, and if
$j~=~m$, then the value computed from $i ^cdot^DELTA v ~+~ v sub 1$ is exactly
$v sub 2$.

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

       glEvalCoord(3G), glEvalMesh(3G), glMap1(3G), glMap2(3G), glMapGrid(3G)

                                                               GLEVALPOINT(3G)