| GLTEXGEN(3G) | GLTEXGEN(3G) |
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 )
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 )
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 = 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 supplied in
params, and xo, yo, zo, and wo 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 p1, p2, p3, and p4). 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 = p1'xe + p2'ye + p3'ze + p4'we
is used, where
(p1' p2' p3' p4') = (p1 p2 p3 p4) M^-1
and xe, ye, ze, and we are the eye coordinates of the vertex, p1, p2, p3, and
p4 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 = (fx fy fz)^T
be the reflection vector such that
f = u - 2 n' n'^T u
Finally, let m = 2 sqrt( fx^2 + fy^2 + (fz + 1)^2). Then the values assigned
to the s and t texture coordinates are
s = (fx/m) + (1/2)
t = (fy/m) + (1/2)
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, glCopyPixels, glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubImage2D, glCopyTexSubImage3D, glTexEnv, glTexImage1D, glTexImage2D, glTexImage3D, glTexParameter, glTexSubImage1D, glTexSubImage2D, glTexSubImage3D