'\"! eqn | mmdoc
'\"macro stdmacro
.ds Vn Version 1.2
.ds Dt 6 March 1997
.ds Re Release 1.1.0
.ds Dp Mar 17 18:05
.ds Dm  Mar  6 20:0
.ds Xs 39427 5 evalpoint.gl
.TH GLEVALPOINT
.SH NAME
.B "glEvalPoint1, glEvalPoint2
\- generate and evaluate a single point in a mesh

.SH C SPECIFICATION
void \f3glEvalPoint1\fP(
GLint \fIi\fP )
.nf
.fi
void \f3glEvalPoint2\fP(
GLint \fIi\fP,
.nf
.ta \w'\f3void \fPglEvalPoint2( 'u
	GLint \fIj\fP )
.fi

.EQ
delim $$
.EN
.SH PARAMETERS
.TP \w'\f2i\fP\ \ 'u 
\f2i\fP
Specifies the integer value for grid domain variable $i$.
.TP
\f2j\fP
Specifies the integer value for grid domain variable $j$
(\f3glEvalPoint2\fP only).
.SH DESCRIPTION
\f3glMapGrid\fP and \f3glEvalMesh\fP are used in tandem to efficiently
generate and evaluate a series of evenly spaced map domain values.
\f3glEvalPoint\fP can be used to evaluate a single grid point in the same gridspace
that is traversed by \f3glEvalMesh\fP.
Calling \f3glEvalPoint1\fP is equivalent to calling
.nf

glEvalCoord1(i . DELTA u + u );
                            1
where 

DELTA u = (u - u  ) / n
            2   1 

and n, u , and u
        1       2

.fi
are the arguments to the most recent \f3glMapGrid1\fP command.
The one absolute numeric requirement is that if $i~=~n$,
then the value computed from 
.nf
i . DELTA u + u  is exactly u .
               1             2

.fi
.P
In the two-dimensional case,
\f3glEvalPoint2\fP,
let 
.nf
DELTA u = (u  - u )/n
            2    1

DELTA v = (v  - v )/m
            2    1

where n, u , u , m, v , and v 
          1   2      1       2

.fi
are the arguments to the most recent \f3glMapGrid2\fP command.
Then the \f3glEvalPoint2\fP command is equivalent to calling
.nf

glEvalCoord2(i .  DELTA u + u , j . DELTA v + v );
                             1                 1

.fi
The only absolute numeric requirements are that if $i~=~n$,
then the value computed from 
.nf

i . DELTA u + u  is exactly u ,
               1             2
.fi
and if $j~=~m$,
then the value computed from 
.nf

j cdot DELTA v + v  is exactly v .
                  1             2
.SH ASSOCIATED GETS
\f3glGet\fP with argument \f3GL_MAP1_GRID_DOMAIN\fP
.br
\f3glGet\fP with argument \f3GL_MAP2_GRID_DOMAIN\fP
.br
\f3glGet\fP with argument \f3GL_MAP1_GRID_SEGMENTS\fP
.br
\f3glGet\fP with argument \f3GL_MAP2_GRID_SEGMENTS\fP
.SH SEE ALSO
\f3glEvalCoord\fP,
\f3glEvalMesh\fP,
\f3glMap1\fP,
\f3glMap2\fP,
\f3glMapGrid\fP