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glEvalMesh1, glEvalMesh2 - compute a one- or two-dimensional grid of
points or lines
void glEvalMesh1( GLenum mode,
GLint i1,
GLint i2 )
eqn not supported
- 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$^cdot^DELTA
u ~+~ u sub 1$ );glEnd();where
$ DELTA u ~=~ (u sub 2 ~-~ u sub 1 ) ^/^ n$
and $n$, $u sub 1$, and $u sub 2$ 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^cdot^DELTA u ~+~ u sub 1$ is exactly
$u sub 2$.
In the two-dimensional case, glEvalMesh2, let
- $ DELTA u ~=~ mark ( u sub 2 ~-~ u sub 1 ) ^/^ n$$ DELTA v ~=~ lineup ( v
sub 2 ~-~ v sub 1 ) ^/^ m$,where $n$, $u sub 1$, $u sub 2$, $m$, $v sub 1$,
and $v sub 2$ 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$^cdot^DELTA u ~+~ u sub 1$, j$^cdot^DELTA
v ~+~ v sub 1$ ); glEvalCoord2( i$^cdot^DELTA u ~+~ u sub 1$, (j+1)$^cdot^DELTA
v ~+~ v sub 1$ ); } 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$^cdot^DELTA u ~+~ u sub 1$, j$^cdot^DELTA
v ~+~ v sub 1$ ); glEnd();}for ( i = i1; i <= i2; i += 1 ) { glBegin(
GL_LINE_STRIP ); for ( j = j1; j <= j1; j += 1 ) glEvalCoord2( i$^cdot^DELTA
u ~+~ u sub 1$, j$^cdot^DELTA v ~+~ v sub 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$^cdot^DELTA u ~+~ u sub 1$, j$^cdot^DELTA
v ~+~ v sub 1$ );glEnd();In all three cases, the only absolute numeric
requirements are that if $i~=~n$,
- then the value computed from $i^cdot^DELTA
u ~+~ u sub 1$ is exactly $u sub 2$, and if $j~=~m$, then the value computed
from $j ^cdot^ DELTA v ~+~ v sub 1$ is exactly $v sub 2$.
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(3G)
, glEvalCoord(3G)
,
glEvalPoint(3G)
, glMap1(3G)
, glMap2(3G)
, glMapGrid(3G)
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