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Table of Contents
glTexGend, glTexGenf, glTexGeni, glTexGendv, glTexGenfv, glTexGeniv
- control the generation of texture coordinates
void glTexGend(
GLenum coord,
GLenum pname,
GLdouble param )
void glTexGenf( GLenum coord,
GLenum pname,
GLfloat param )
void glTexGeni( GLenum coord,
GLenum pname,
GLint param )
eqn not supported
- coord
- Specifies a texture coordinate. Must be
one of GL_S, GL_T, GL_R, or GL_Q.
- pname
- Specifies the symbolic name of the
texture-coordinate generation function. Must be GL_TEXTURE_GEN_MODE.
- param
- Specifies a single-valued texture generation parameter, one of GL_OBJECT_LINEAR,
GL_EYE_LINEAR, or GL_SPHERE_MAP.
void glTexGendv( GLenum
coord,
GLenum pname,
const GLdouble *params )
void glTexGenfv( GLenum coord,
GLenum pname,
const GLfloat *params )
void glTexGeniv( GLenum coord,
GLenum pname,
const GLint *params )
- coord
- Specifies a texture coordinate. Must be one of GL_S, GL_T,
GL_R, or GL_Q.
- pname
- Specifies the symbolic name of the texture-coordinate
generation function or function parameters. Must be GL_TEXTURE_GEN_MODE,
GL_OBJECT_PLANE, or GL_EYE_PLANE.
- params
- Specifies a pointer to an array
of texture generation parameters. If pname is GL_TEXTURE_GEN_MODE, then
the array must contain a single symbolic constant, one of GL_OBJECT_LINEAR,
GL_EYE_LINEAR, or GL_SPHERE_MAP. Otherwise, params holds the coefficients
for the texture-coordinate generation function specified by pname.
glTexGen
selects a texture-coordinate generation function or supplies coefficients
for one of the functions. coord names one of the (s, t, r, q) texture coordinates;
it must be one of the symbols GL_S, GL_T, GL_R, or GL_Q. pname must be one
of three symbolic constants: GL_TEXTURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE.
If pname is GL_TEXTURE_GEN_MODE, then params chooses a mode, one of GL_OBJECT_LINEAR,
GL_EYE_LINEAR, or GL_SPHERE_MAP. If pname is either GL_OBJECT_PLANE or
GL_EYE_PLANE, params contains coefficients for the corresponding texture
generation function.
If the texture generation function is GL_OBJECT_LINEAR,
the function
$g ~=~ p sub 1^x sub o ~+~ p sub 2^y sub o ~+~ p sub 3^z sub
o ~+~ p sub 4^w sub o$
is used, where $g$ is the value computed for the coordinate named in coord,
$p sub 1$, $p sub 2$, $p sub 3$, and $p sub 4$ are the four values supplied
in params, and $x sub o$, $y sub o$, $z sub o$, and $w sub o$ are the object
coordinates of the vertex. This function can be used, for example, to texture-map
terrain using sea level as a reference plane (defined by $p sub 1$, $p
sub 2$, $p sub 3$, and $p sub 4$). The altitude of a terrain vertex is
computed by the GL_OBJECT_LINEAR coordinate generation function as its
distance from sea level; that altitude can then be used to index the texture
image to map white snow onto peaks and green grass onto foothills.
If the
texture generation function is GL_EYE_LINEAR, the function
$g ~=~ p sub
1 sup prime ^x sub e ~+~ p sub 2 sup prime ^y sub e ~+~ p sub 3 sup prime
^z sub e ~+~ p sub 4 sup prime ^w sub e$
is used, where
$( p sub 1 sup prime ~~p sub 2 sup prime~~p sub 3 sup prime~~
{ p sub 4 sup prime}) ~=~ ( p sub 1~~ p sub 2~~ p sub 3~~ p sub 4 ) ~M
sup -1$
and $x sub e$, $y sub e$, $z sub e$, and $w sub e$ are the eye coordinates
of the vertex, $p sub 1$, $p sub 2$, $p sub 3$, and $p sub 4$ are the values
supplied in params, and $M$ is the modelview matrix when glTexGen is invoked.
If $M$ is poorly conditioned or singular, texture coordinates generated
by the resulting function may be inaccurate or undefined.
Note that the
values in params define a reference plane in eye coordinates. The modelview
matrix that is applied to them may not be the same one in effect when the
polygon vertices are transformed. This function establishes a field of
texture coordinates that can produce dynamic contour lines on moving objects.
If pname is GL_SPHERE_MAP and coord is either GL_S or GL_T, $s$ and $t$
texture coordinates are generated as follows. Let u be the unit vector
pointing from the origin to the polygon vertex (in eye coordinates). Let
n sup prime be the current normal, after transformation to eye coordinates.
Let
$f ~=~ ( f sub x~~f sub y~~f sub z ) sup T$ be the reflection vector
such that
$f ~=~ u ~-~ 2 n sup prime n sup prime sup T u$
Finally, let $ m ~=~ 2 sqrt { f sub x sup {~2} ~+~ f sub y sup {~2} ~+~
(f sub z ~+~ 1 ) sup 2}$. Then the values assigned to the $s$ and $t$ texture
coordinates are
$s ~=~ f sub x over m ~+~ 1 over 2$
$t ~=~ f sub y over
m ~+~ 1 over 2$
To enable or disable a texture-coordinate generation function,
call glEnable or glDisable with one of the symbolic texture-coordinate names
(GL_TEXTURE_GEN_S, GL_TEXTURE_GEN_T, GL_TEXTURE_GEN_R, or GL_TEXTURE_GEN_Q)
as the argument. When enabled, the specified texture coordinate is computed
according to the generating function associated with that coordinate. When
disabled, subsequent vertices take the specified texture coordinate from
the current set of texture coordinates. Initially, all texture generation
functions are set to GL_EYE_LINEAR and are disabled. Both $s$ plane equations
are (1, 0, 0, 0), both $t$ plane equations are (0, 1, 0, 0), and all $r$
and $q$ plane equations are (0, 0, 0, 0).
When the GL_ARB_multitexture extension
is supported, glTexGen set the texture generation parameters for the currently
active texture unit, selected with glActiveTextureARB.
GL_INVALID_ENUM
is generated when coord or pname is not an accepted defined value, or when
pname is GL_TEXTURE_GEN_MODE and params is not an accepted defined value.
GL_INVALID_ENUM is generated when pname is GL_TEXTURE_GEN_MODE, params
is GL_SPHERE_MAP, and coord is either GL_R or GL_Q.
GL_INVALID_OPERATION
is generated if glTexGen is executed between the execution of glBegin and
the corresponding execution of glEnd.
glGetTexGen
glIsEnabled with argument GL_TEXTURE_GEN_S
glIsEnabled with argument GL_TEXTURE_GEN_T
glIsEnabled with argument GL_TEXTURE_GEN_R
glIsEnabled with argument GL_TEXTURE_GEN_Q
glActiveTextureARB(3G)
,
glCopyPixels(3G)
, glCopyTexImage2D(3G)
, glCopyTexSubImage1D(3G)
, glCopyTexSubImage2D(3G)
,
glCopyTexSubImage3D(3G)
, glTexEnv(3G)
, glTexImage1D(3G)
, glTexImage2D(3G)
,
glTexImage3D(3G)
, glTexParameter(3G)
, glTexSubImage1D(3G)
, glTexSubImage2D(3G)
,
glTexSubImage3D(3G)
Table of Contents
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