NAME

C SPECIFICATION

	GLint i1,
	GLint i2 )

PARAMETERS

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 $i$ .

C SPECIFICATION

	GLint i1,
	GLint i2,
	GLint j1,
	GLint j2 )

PARAMETERS

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 $j$ .

DESCRIPTION

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();

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

and n, u, and u  are the arguments to the most recent
        1      2

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

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

ERRORS

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

ASSOCIATED GETS

SEE ALSO