GLTEXGEN(3G) UNIX Programmer's Manual GLTEXGEN(3G)
NAME
glTexGend, glTexGenf, glTexGeni, glTexGendv, glTexGenfv,
glTexGeniv - control the generation of texture coordinates
C SPECIFICATION
void glTexGend( GLenum coord,
GLenum pname,
GLdouble param )
void glTexGenf( GLenum coord,
GLenum pname,
GLfloat param )
void glTexGeni( GLenum coord,
GLenum pname,
GLint param )
PARAMETERS
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 parame-
ter, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, or
GL_SPHERE_MAP.
C SPECIFICATION
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 )
PARAMETERS
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
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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. Oth-
erwise, params holds the coefficients for the texture-
coordinate generation function specified by pname.
DESCRIPTION
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 func-
tion.
If the texture generation function is GL_OBJECT_LINEAR, the
function
g = p1xo + p2yo + p3zo + p4wo
is used, where g is the value computed for the coordinate
named in coord, p1, p2, p3, and p4 are the four values sup-
plied in params, and xo, yo, zo, and wo are the object coor-
dinates of the vertex. This function can be used, for exam-
ple, to texture-map terrain using sea level as a reference
plane (defined by p1, p2, p3, and p4). The altitude of a
terrain vertex is computed by the GL_OBJECT_LINEAR coordi-
nate 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.
') = (p1 p2 p3 'p4) M-1
If the texture gener'tip4 function'ze G+L_pE4YE_LINEAR, the
iasndusxeed,,ye,eze, andpwe are the eye3coordinates of the ver-
tex, p1, p2,'p3,2and'p4 are2the values supplied in params,
and M is the1modelview matrix when glTexGen is invoked. If M
is poorly conditioned or singular, texture coordinates gen-
erated by the resulting function may be inaccurate or unde-
fined.
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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 ver-
tices 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 = (fx fy fz)T
be the reflection vector such that
2 + (fz + 1)2. Then the values
assigned to the s and__t__te_xyt_ur_e_'c_o_11__r_dinates are
|fx ____ + 2
Tonenablelor disable a tetxt=urme-coordinate generation func-
tion, 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.
ERRORS
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.
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GL_INVALID_OPERATION is generated if glTexGen is executed
between the execution of glBegin and the corresponding exe-
cution of glEnd.
ASSOCIATED GETS
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
SEE ALSO
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)
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