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·Δu+u1 );
where Δu=(u2−u1)/n
and n, u1, and u2 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·Δu+u1 is exactly u2.
In the two-dimensional case, glEvalPoint2, let
Δu=(u2−u1)/n Δv=(v2−v1)/m
where n, u1, u2, m, v1, and v2 are the arguments to the most recent glMapGrid2 command. Then the glEvalPoint2 command is equivalent to calling
glEvalCoord2( i·Δu+u1, j·Δv+v1 );
The only absolute numeric requirements are that if i=n, then the value computed from i·Δu+u1 is exactly u2, and if j=m, then the value computed from i·Δv+v1 is exactly v2.