eqn
not supported
Recall that
$0 sup 0 ~==~ 1 $ and $ left ( ^ down 20 {cpile
{ n above 0 }} ~^ right ) ~~==~~ 1 $
glMap2 is used to define the basis and
to specify what kind of values
are produced. Once defined, a map can be
enabled and disabled by calling glEnable and glDisable with the map name,
one of the nine predefined values for target, described below. When glEvalCoord2
presents values $u$ and $v$, the bivariate Bernstein polynomials are evaluated
using $u hat$ and $v hat$, where
$u hat ~~=~~ {u ~-~ "u1"} over {"u2" ~-~
"u1"}$
$v hat ~~=~~ {v ~-~ "v1"} over {"v2" ~-~ "v1"}$
target is a symbolic
constant that indicates what kind of control points
are provided in points,
and what output is generated when the map is evaluated. It can assume one
of nine predefined values:
- GL_MAP2_VERTEX_3
- Each control point is three
floating-point values representing $x$, $y$, and $z$. Internal glVertex3
commands are generated when the map is evaluated.
- GL_MAP2_VERTEX_4
- Each
control point is four floating-point values representing $x$, $y$, $z$,
and $w$. Internal glVertex4 commands are generated when the map is evaluated.
- GL_MAP2_INDEX
- Each control point is a single floating-point value representing
a color index. Internal glIndex commands are generated when the map is evaluated
but the current index is not updated with the value of these glIndex commands.
- GL_MAP2_COLOR_4
- Each control point is four floating-point values representing
red, green, blue, and alpha. Internal glColor4 commands are generated when
the map is evaluated but the current color is not updated with the value
of these glColor4 commands.
- GL_MAP2_NORMAL
- Each control point is three floating-point
values representing the $x$, $y$, and $z$ components of a normal vector.
Internal glNormal commands are generated when the map is evaluated but
the current normal is not updated with the value of these glNormal commands.
- GL_MAP2_TEXTURE_COORD_1
- Each control point is a single floating-point value
representing the $s$ texture coordinate. Internal
glTexCoord1 commands are generated when the map is evaluated but the current
texture coordinates are not updated with the value of these glTexCoord
commands.
GL_MAP2_TEXTURE_COORD_2
Each control point is two floating-point
values representing the $s$ and $t$ texture coordinates. Internal
glTexCoord2 commands are generated when the map is evaluated but the current
texture coordinates are not updated with the value of these glTexCoord
commands.
GL_MAP2_TEXTURE_COORD_3
Each control point is three floating-point
values representing the $s$, $t$, and $r$ texture coordinates. Internal
glTexCoord3 commands are generated when the map is evaluated but the current
texture coordinates are not updated with the value of these glTexCoord
commands.
GL_MAP2_TEXTURE_COORD_4
Each control point is four floating-point
values representing the $s$, $t$, $r$, and $q$ texture coordinates. Internal
glTexCoord4 commands are generated when the map is evaluated but the current
texture coordinates are not updated with the value of these glTexCoord
commands.
ustride, uorder, vstride, vorder, and points define the array
addressing for accessing the control points. points is the location of the
first control point, which occupies one, two, three, or four contiguous
memory locations, depending on which map is being defined. There are $ "uorder"
~times~ "vorder" $ control points in the array. ustride specifies how many
float or double locations are skipped to advance the internal memory pointer
from control point $R sub {i j} $ to control point $R sub {(i+1) j} $. vstride
specifies how many float or double locations are skipped to advance the
internal memory pointer from control point $R sub {i j} $ to control point
$R sub {i (j+1) } $.
As is the case with all GL commands that accept
pointers to data, it is as if the contents of points were copied by glMap2
before glMap2 returns. Changes to the contents of points have no effect
after glMap2 is called.
Initially, GL_AUTO_NORMAL is enabled. If GL_AUTO_NORMAL
is enabled, normal vectors are generated when either GL_MAP2_VERTEX_3 or
GL_MAP2_VERTEX_4 is used to generate vertices.
GL_INVALID_ENUM is
generated if target is not an accepted value.
GL_INVALID_VALUE is generated
if u1 is equal to u2, or if v1 is equal to v2.
GL_INVALID_VALUE is generated
if either ustride or vstride is less than the number of values in a control
point.
GL_INVALID_VALUE is generated if either uorder or vorder is less
than 1 or greater than the return value of GL_MAX_EVAL_ORDER.
GL_INVALID_OPERATION
is generated if glMap2 is executed between the execution of glBegin and
the corresponding execution of glEnd.
When the GL_ARB_multitexture extension
is supported, GL_INVALID_OPERATION is generated if glMap2 is called and
the value of GL_ACTIVE_TEXTURE_ARB is not GL_TEXTURE0_ARB.
glGetMap
glGet with argument GL_MAX_EVAL_ORDER
glIsEnabled with argument GL_MAP2_VERTEX_3
glIsEnabled with argument GL_MAP2_VERTEX_4
glIsEnabled with argument GL_MAP2_INDEX
glIsEnabled with argument GL_MAP2_COLOR_4
glIsEnabled with argument GL_MAP2_NORMAL
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_1
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_2
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_3
glIsEnabled with argument GL_MAP2_TEXTURE_COORD_4
glBegin(3G)
,
glColor(3G)
, glEnable(3G)
, glEvalCoord(3G)
, glEvalMesh(3G)
, glEvalPoint(3G)
,
glMap1(3G)
, glMapGrid(3G)
, glNormal(3G)
, glTexCoord(3G)
, glVertex(3G)