NAME
fglTexGend, fglTexGenf, fglTexGeni, fglTexGendv,
fglTexGenfv, fglTexGeniv - control the generation of texture
coordinates
FORTRAN SPECIFICATION
SUBROUTINE fglTexGend( INTEGER*4 coord,
INTEGER*4 pname,
REAL*8 param )
SUBROUTINE fglTexGenf( INTEGER*4 coord,
INTEGER*4 pname,
REAL*4 param )
SUBROUTINE fglTexGeni( INTEGER*4 coord,
INTEGER*4 pname,
INTEGER*4 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
parameter, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR,
or GL_SPHERE_MAP.
FORTRAN SPECIFICATION
SUBROUTINE fglTexGendv( INTEGER*4 coord,
INTEGER*4 pname,
CHARACTER*8 params )
SUBROUTINE fglTexGenfv( INTEGER*4 coord,
INTEGER*4 pname,
CHARACTER*8 params )
SUBROUTINE fglTexGeniv( INTEGER*4 coord,
INTEGER*4 pname,
CHARACTER*8 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
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.
DESCRIPTION
fglTexGen 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 x +p y +p z +p w
1 o 2 o 3 o 4 o
is used, where g is the value computed for the coordinate
named in coord, p , p , p , and p are the four values
supplied in param<EM>s, and x3, y , z4, and w are the object
coordinates of the vertex. This functionocan be used, for
example, to texture-map terrain using sea level as a
reference plane (defined by p , p , p , and p ). 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 ' x +p ' y +p ' z +p ' w
1 e 2 e 3 e 4 e
is used, where
(p ' p ' p ' p ')=(p p p p ) M-1
1 2 3 4 1 2 3 4
and x , y , z , and w are the eye coordinates of the
vertex, pe, pe, p , and p are the values supplied in
params, and M2is the modelview matrix when fglTexGen 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 f f )T
be the reflection vector such that z
' 'T
f = u - 2n n u
_______________
Finally, let m = 2 |f 2+f 2+(f +1)2. Then the values
assigned to the s andxt texture coordinates are
__ _
s = m + 2
f
t = __ + _
m 2
To enable or disable a texture-coordinate generation
function, call fglEnable or fglDisable 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).
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.
GL_INVALID_OPERATION is generated if fglTexGen is executed
between the execution of fglBegin and the corresponding
execution of fglEnd.
ASSOCIATED GETS
fglGetTexGen
fglIsEnabled with argument GL_TEXTURE_GEN_S
fglIsEnabled with argument GL_TEXTURE_GEN_T
fglIsEnabled with argument GL_TEXTURE_GEN_R
fglIsEnabled with argument GL_TEXTURE_GEN_Q
SEE ALSO
fglCopyPixels, fglCopyTexImage2D, fglCopyTexSubImage1D,
fglCopyTexSubImage2D, fglTexEnv, fglTexImage1D,
fglTexImage2D, fglTexParameter, fglTexSubImage1D,
fglTexSubImage2D