glEvalMesh1, glEvalMesh2 - compute a one- or two-dimensional
grid of points or lines

glEvalMesh1
	glEvalMesh1(mode, i1, i2) -> None
glEvalMesh2
	glEvalMesh2(mode, i1, i2, j1, j2) -> None

void glEvalMesh1( GLenum mode,
                  GLint i1,
                  GLint i2 )

mode	In glEvalMesh1,	specifies whether to compute a one-
      dimensional mesh of points or lines.  Symbolic
      constants GL_POINT and GL_LINE are accepted.

i1, i2
      Specify	the first and last integer values for grid
      domain variable	i.

void glEvalMesh2( GLenum mode,
                  GLint i1,
                  GLint i2,
                  GLint j1,
                  GLint j2 )

mode In glEvalMesh2, specifies whether to compute a two-
     dimensional mesh	of points, lines, or polygons.
     Symbolic	constants GL_POINT, GL_LINE, and GL_FILL are
     accepted.

i1, i2
     Specify the first and last integer values for grid
     domain variable i.

j1, j2
     Specify the first and last integer values for grid
     domain variable j.

glMapGrid and	glEvalMesh are used in tandem to efficiently
generate and evaluate	a series of evenly-spaced map domain
values.  glEvalMesh steps through the	integer	domain of a
one- or two-dimensional grid,	whose range is the domain of
the evaluation maps specified	by glMap1 and glMap2.  mode
determines whether the resulting vertices are	connected as
points, lines, or filled polygons.

In the one-dimensional case, glEvalMesh1, the	mesh is
generated as if the following	code fragment were executed:

glBegin (type);
for (i = i1; i <= i2;	i += 1)
     glEvalCoord1(i .	DELTA u	+ u sub	1)
glEnd();

where

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

and n, u, and	u  are the arguments to	the most recent
        1	 2
glMapGrid1 command.  type is GL_POINTS if mode is GL_POINT,
or GL_LINES if mode is GL_LINE.

The one absolute numeric requirement is that if i = n, then
the value computed from

i . DELTA u +	u

is exactly u.

In the two-dimensional case, glEvalMesh2, let

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
are the arguments to the most	recent glMapGrid2 command.
Then,	if mode	is GL_FILL, the	glEvalMesh2 command is
equivalent to:

for (j = j1;	j < j2;	j += 1)	{
    glBegin (GL_QUAD_STRIP);
    for (i = i1; i <=	i2; i += 1) {
        glEvalCoord2(i . DELTA u + u , j . DELTA v + v );
                                    1			1
        glEvalCoord2(i . DELTA u + u , (j+1) . DELTA v + v );
                                    1			    1
    }
    glEnd();
}

If mode is GL_LINE, then a call to glEvalMesh2 is equivalent
to:
for (j = j1;	j <= j2; j += 1) {
    glBegin(GL_LINE_STRIP);
    for (i = i1; i <=	i2; i += 1)
        glEvalCoord2(i . DELTA u + u , j . DELTA v + v );
                                    1			1
    glEnd();
}
for (i = i1;	i <= i2; i += 1) {
    glBegin(GL_LINE_STRIP);
    for (j = j1; j <=	j1; j += 1)
        glEvalCoord2)(i . DELTA u + u	, j . DELTA v +	v );
                                     1		 1
    glEnd();
}

And finally, if mode is GL_POINT, then a call	to glEvalMesh2
is equivalent	to:

glBegin (GL_POINTS);
for (j = j1;	j <= j2; j += 1) {
    for (i = i1; i <=	i2; i += 1) {
        glEvalCoord2(i . DELTA u + u , j . DELTA v + v );
                                    1			1
    }
}
glEnd();

In all three cases, the only absolute	numeric	requirements
are that if i	= n, then the value computed from
i . DELTA u +	u is exactly u ,
               1	      2
and if j = m,
then the value computed from
j . DELTA v +	v is exactly v .
               1	      2

GL_INVALID_ENUM is generated if mode is not an accepted
value.

GL_INVALID_OPERATION is generated if glEvalMesh is executed
between the execution	of glBegin and the corresponding
execution of glEnd.

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

glBegin, glEvalCoord,	glEvalPoint, glMap1, glMap2, glMapGrid