fglEvalMesh(3G) OpenGL Reference fglEvalMesh(3G)NAME
fglEvalMesh1, fglEvalMesh2 - compute a one- or two-dimensional grid of
points or lines
FORTRAN SPECIFICATION
SUBROUTINE fglEvalMesh1( INTEGER*4 mode,
INTEGER*4 i1,
INTEGER*4 i2 )
PARAMETERS
mode In fglEvalMesh1, 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.
FORTRAN SPECIFICATION
SUBROUTINE fglEvalMesh2( INTEGER*4 mode,
INTEGER*4 i1,
INTEGER*4 i2,
INTEGER*4 j1,
INTEGER*4 j2 )
PARAMETERS
mode In fglEvalMesh2, 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
fglMapGrid and fglEvalMesh are used in tandem to efficiently generate and
evaluate a series of evenly-spaced map domain values. fglEvalMesh steps
through the integer domain of a one- or two-dimensional grid, whose range
is the domain of the evaluation maps specified by fglMap1 and fglMap2.
mode determines whether the resulting vertices are connected as points,
lines, or filled polygons.
In the one-dimensional case, fglEvalMesh1, the mesh is generated as if
the following code fragment were executed:
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fglEvalMesh(3G) OpenGL Reference fglEvalMesh(3G)
glBegin( type );
for ( i = i1; i <= i2; i += 1 )
.
glEvalCoord1( i Wu + u );
1
glEnd();
where
Wu = (u - u )/n
2 1
and n, u , and u are the arguments to the most recent fglMapGrid1
1 2
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 Wu + u is exactly u .
1 2
In the two-dimensional case, fglEvalMesh2, let
Wu = (u - u )/n
2 1
Wv = (v - v )/m,
2 1
where n, u , u , m, v , and v are the arguments to the most recent
1 2 1 2
fglMapGrid2 command. Then, if mode is GL_FILL, the fglEvalMesh2 command
is equivalent to:
for ( j = j1; j < j2; j += 1 ) {
glBegin( GL_QUAD_STRIP );
for ( i = i1; i <= i2; i += 1 ) {
. .
glEvalCoord2( i Wu + u , j Wv + v );
1 1
. .
glEvalCoord2( i Wu + u , (j+1) Wv + v );
1 1
}
glEnd();
}
If mode is GL_LINE, then a call to fglEvalMesh2 is equivalent to:
for ( j = j1; j <= j2; j += 1 ) {
glBegin( GL_LINE_STRIP );
for ( i = i1; i <= i2; i += 1 )
. .
glEvalCoord2( i Wu + u , j Wv + v );
1 1
glEnd();
}
for ( i = i1; i <= i2; i += 1 ) {
glBegin( GL_LINE_STRIP );
for ( j = j1; j <= j1; j += 1 )
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fglEvalMesh(3G) OpenGL Reference fglEvalMesh(3G)
. .
glEvalCoord2( i Wu + u , j Wv + v );
1 1
glEnd();
}
And finally, if mode is GL_POINT, then a call to fglEvalMesh2 is
equivalent to:
glBegin( GL_POINTS );
for ( j = j1; j <= j2; j += 1 )
for ( i = i1; i <= i2; i += 1 )
. .
glEvalCoord2( i Wu + u , j Wv + v );
1 1
glEnd();
In all three cases, the only absolute numeric requirements are that if
.
i = n, then the value computed from i Wu + u is exactly u , and if
1 2
.
j = m, then the value computed from j Wv + v is exactly v .
1 2
ERRORS
GL_INVALID_ENUM is generated if mode is not an accepted value.
GL_INVALID_OPERATION is generated if fglEvalMesh is executed between the
execution of fglBegin and the corresponding execution of fglEnd.
ASSOCIATED GETS
fglGet with argument GL_MAP1_GRID_DOMAIN
fglGet with argument GL_MAP2_GRID_DOMAIN
fglGet with argument GL_MAP1_GRID_SEGMENTS
fglGet with argument GL_MAP2_GRID_SEGMENTS
MACHINE DEPENDENCIES
RealityEngine, RealityEngine2, and VTX systems do not handle 1D maps for
colors correctly.
SEE ALSO
fglBegin, fglEvalCoord, fglEvalPoint, fglMap1, fglMap2, fglMapGrid
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