glEvalMesh(3) glEvalMesh(3)
NAME
glEvalMesh1, glEvalMesh2 - compute a one- or two-dimensional grid of
points or lines
C SPECIFICATION
void glEvalMesh1( GLenum mode,
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 vari-
able i.
C SPECIFICATION
void glEvalMesh2( GLenum mode,
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 vari-
able i.
j1, j2 Specify the first and last integer values for grid domain vari-
able j.
DESCRIPTION
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 dot DELTA u + u1 );
glEnd();
where
DELTA(u) = (u2 - u1 ) / n
and n, u1, and u2 are the arguments to the most recent 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 dot DELTA(u) + u1 is exactly u2.
In the two-dimensional case, glEvalMesh2, let
DELTA(u) = ( u2 - u1 ) / n
DELTA(v) = ( v2 - v1 ) / m,
where n, u1, u2, m, v1, and v2 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 dot DELTA(u) + u1, j dot DELTA(v) + v1 );
glEvalCoord2( i dot DELTA(u) + u1, (j+1) dot DELTA(v) + v1 );
}
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 dot DELTA(u) + u1, j dot DELTA(v) + v1 );
glEnd();
}
for ( i = i1; i <= i2; i += 1 ) {
glBegin( GL_LINE_STRIP );
for ( j = j1; j <= j1; j += 1 )
glEvalCoord2( i dot DELTA(u) + u1, j dot v + v1 );
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 dot u + u1, j dot DELTA(v) + v1 );
glEnd();
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.
ERRORS
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.
ASSOCIATED GETS
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
SEE ALSO
glBegin(3), glEvalCoord(3), glEvalPoint(3), glMap1(3), glMap2(3),
glMapGrid(3)
glEvalMesh(3)
Mac OS X 10.6 - Generated Thu Sep 17 20:20:19 CDT 2009