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 glEvalPoint 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 glMapGrid1 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
In the two-dimensional case,
glEvalPoint ,
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 glMapGrid2 command.
Then the glEvalPoint 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