'\" e  
'\"macro stdmacro
.ds Vn Version 1.2
.ds Dt 24 September 1999
.ds Re Release 1.2.1
.ds Dp May 22 14:45
.ds Dm 4 May 22 14:
.ds Xs 32277     7
.TH GLEVALMESH 3G
.SH NAME
.B "glEvalMesh1, glEvalMesh2
\- compute a one- or two-dimensional grid of points or lines

.SH C SPECIFICATION
void \f3glEvalMesh1\fP(
GLenum \fImode\fP,
.nf
.ta \w'\f3void \fPglEvalMesh1( 'u
	GLint \fIi1\fP,
	GLint \fIi2\fP )
.fi

.SH PARAMETERS
.TP \w'\f2mode\fP\ \ 'u 
\f2mode\fP
In \%\f3glEvalMesh1\fP, specifies whether to compute a one-dimensional mesh of points or lines.
Symbolic constants
\%\f3GL_POINT\fP and
\%\f3GL_LINE\fP are accepted.
.TP
\f2i1\fP, \f2i2\fP
Specify the first and last integer values for grid domain variable i.
.SH C SPECIFICATION
void \f3glEvalMesh2\fP(
GLenum \fImode\fP,
.nf
.ta \w'\f3void \fPglEvalMesh2( 'u
	GLint \fIi1\fP,
	GLint \fIi2\fP,
	GLint \fIj1\fP,
	GLint \fIj2\fP )
.fi

.SH PARAMETERS
.TP
\f2mode\fP
In \%\f3glEvalMesh2\fP, specifies whether to compute a two-dimensional mesh of points, lines,
or polygons.
Symbolic constants
\%\f3GL_POINT\fP,
\%\f3GL_LINE\fP, and
\%\f3GL_FILL\fP are accepted.
.TP
\f2i1\fP, \f2i2\fP
Specify the first and last integer values for grid domain variable i.
.TP
\f2j1\fP, \f2j2\fP
Specify the first and last integer values for grid domain variable j.
.SH DESCRIPTION
\%\f3glMapGrid\fP and \%\f3glEvalMesh\fP are used in tandem to efficiently
generate and evaluate a series of evenly-spaced map domain values.
\%\f3glEvalMesh\fP steps through the integer domain of a one- or two-dimensional grid,
whose range is the domain of the evaluation maps specified by
\%\f3glMap1\fP and \%\f3glMap2\fP.
\f2mode\fP determines whether the resulting vertices are connected as
points,
lines,
or filled polygons.
.P
In the one-dimensional case,
\%\f3glEvalMesh1\fP,
the mesh is generated as if the following code fragment were executed:
.nf
.IP
\f7
glBegin( \f2type\f7 );
for ( i = \f2i1\fP; i <= \f2i2\fP; i += 1 )
   glEvalCoord1( i dot DELTA u + u1 );
glEnd();
\fP
.RE
.fi
where
.sp
.in
DELTA(u) = (u2 - u1 ) / n
.sp
.in 0
.P
and n, u1, and u2 are the arguments to the most recent
\%\f3glMapGrid1\fP command.
\f2type\fP is \%\f3GL_POINTS\fP if \f2mode\fP is \%\f3GL_POINT\fP,
or \%\f3GL_LINES\fP if \f2mode\fP is \%\f3GL_LINE\fP.
.P
The one absolute numeric requirement is that if i = n, then the
value computed from i dot DELTA(u) + u1 is exactly u2.
.P
In the two-dimensional case, \%\f3glEvalMesh2\fP, let 
.nf
.IP
DELTA(u) = ( u2 - u1 ) / n
.sp
DELTA(v) = ( v2 - v1 ) / m,
.fi
.RE
.P
where n, u1, u2, m, v1, and v2 are the
arguments to the most recent \%\f3glMapGrid2\fP command.  Then, if
\f2mode\fP is \%\f3GL_FILL\fP, the \%\f3glEvalMesh2\fP command is equivalent
to:
.nf
.IP
\f7
for ( j = \f2j1\fP; j < \f2j2\fP; j += 1 ) {
   glBegin( GL_QUAD_STRIP );
   for ( i = \f2i1\fP; i <= \f2i2\fP; i += 1 ) {
      glEvalCoord2( i dot DELTA(u) + u1, j dot DELTA(v) + v1 );
      glEvalCoord2( i dot DELTA(u) + u1, (j+1) dot DELTA(v) + v1 );
   }
   glEnd();
}
\fP
.RE
.fi
.P
If \f2mode\fP is \%\f3GL_LINE\fP, then a call to \%\f3glEvalMesh2\fP is equivalent to:
.nf
.IP
\f7
for ( j = \f2j1\fP; j <= \f2j2\fP; j += 1 ) {
   glBegin( GL_LINE_STRIP );
   for ( i = \f2i1\fP; i <= \f2i2\fP; i += 1 )
      glEvalCoord2( i dot DELTA(u) + u1, j dot DELTA(v) + v1 );
   glEnd();
}
.sp
for ( i = \f2i1\fP;  i <= \f2i2\fP; i += 1 ) {
   glBegin( GL_LINE_STRIP );
   for ( j = \f2j1\fP; j <= \f2j1\fP; j += 1 )
      glEvalCoord2( i dot DELTA(u) + u1, j dot v + v1 );
   glEnd();
}
\fP
.RE
.fi
.P
And finally, if \f2mode\fP is \%\f3GL_POINT\fP, then a call to
\%\f3glEvalMesh2\fP is equivalent to:
.nf
.IP
\f7
glBegin( GL_POINTS );
for ( j = \f2j1\fP; j <= \f2j2\fP; j += 1 )
   for ( i = \f2i1\fP; i <= \f2i2\fP; i += 1 )
      glEvalCoord2( i dot u + u1, j dot DELTA(v) + v1 );
glEnd();
\fP
.RE
.fi
.P
In all three cases, the only absolute numeric requirements are that if i = n,
then the value computed from i dot DELTA(u) + u1 is exactly u2, and if j = m, then the value computed from
j dot DELTA(v) + v1 is exactly v2.
.SH ERRORS
\%\f3GL_INVALID_ENUM\fP is generated if \f2mode\fP is not an accepted value.
.P
\%\f3GL_INVALID_OPERATION\fP is generated if \%\f3glEvalMesh\fP
is executed between the execution of \%\f3glBegin\fP
and the corresponding execution of \%\f3glEnd\fP.
.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
\%\f3glBegin\fP,
\%\f3glEvalCoord\fP,
\%\f3glEvalPoint\fP,
\%\f3glMap1\fP,
\%\f3glMap2\fP,
\%\f3glMapGrid\fP