glTexGen, 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 );
Specifies a texture coordinate. Must be one of GL_S, GL_T,
GL_R, or GL_Q. Specifies the symbolic name of the texture-coordinate
generation function. Must be GL_TEXTURE_GEN_MODE.
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 );
Specifies a texture coordinate. Must be one of GL_S, GL_T,
GL_R, or GL_Q. 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. 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 texturecoordinate
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[1]x[o] + p[2]y[o] + p[3]z[o] + p[4]w[o]
is used, where g is the value computed for the coordinate
named in coord, p[1], p[2], p[3], and p[4] are the four
values supplied in params, and x[o], y[o], z[o], and w[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[1], p[2], p[3],
and p[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[1 ]prime x[e] + p[2 ]prime y[e] + p[3
]prime z[e] + p[4 ]prime w[e]
g = p[1]prime x[e] + p[2]prime y[e] + p[3]prime z[e] +
p[4] prime w[e]
is used, where
( p[1]prime p[2 ]prime P[3] prime p[4 ]prime) = ( p[1]
p[2] p[3] p[4] ) M^-1
and x[e], y[e], z[e], and w[e] are the eye coordinates of
the vertex, p[1], p[2], p[3], and p[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[x]f[y]f[z] )^T
be the reflection vector such that f = u - 2 n prime n
prime^T u
Finally, let m = 2 sqrt f[x^2] + f[y^2]+ (f[z] + 1 )^2.
Then the values assigned to the s and t texture coordinates
are s = f[x] over m + 1 over 2
t = f[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(3), glCopyPixels(3), glCopyTexImage2D(3), glCopyTexSubImage1D(3), glCopyTexSubImage2D(3),
glCopyTexSubImage3D(3), glTexEnv(3), glTexImage1D(3),
glTexImage2D(3), glTexImage3D(3), , glTexParameter(3),
glTexSubImage1D(3), glTexSubImage2D(3), glTexSubImage3D(3)
glTexGen(3G)
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