<HTML>
<BODY>
<PRE>
<STRONG>NAME</STRONG>
<STRONG>glTexGend,</STRONG> <STRONG>glTexGenf,</STRONG> <STRONG>glTexGeni,</STRONG> <STRONG>glTexGendv,</STRONG> <STRONG>glTexGenfv,</STRONG>
<STRONG>glTexGeniv</STRONG> - control the generation of texture coordinates
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glTexGend</STRONG>( GLenum <EM>coord</EM>,
GLenum <EM>pname</EM>,
GLdouble <EM>param</EM> )
void <STRONG>glTexGenf</STRONG>( GLenum <EM>coord</EM>,
GLenum <EM>pname</EM>,
GLfloat <EM>param</EM> )
void <STRONG>glTexGeni</STRONG>( GLenum <EM>coord</EM>,
GLenum <EM>pname</EM>,
GLint <EM>param</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>coord</EM> Specifies a texture coordinate. Must be one of
<STRONG>GL_S</STRONG>, <STRONG>GL_T</STRONG>, <STRONG>GL_R</STRONG>, or <STRONG>GL_Q</STRONG>.
<EM>pname</EM> Specifies the symbolic name of the texture-
coordinate generation function. Must be
<STRONG>GL_TEXTURE_GEN_MODE</STRONG>.
<EM>param</EM> Specifies a single-valued texture generation
parameter, one of <STRONG>GL_OBJECT_LINEAR</STRONG>, <STRONG>GL_EYE_LINEAR</STRONG>,
or <STRONG>GL_SPHERE_MAP</STRONG>.
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glTexGendv</STRONG>( GLenum <EM>coord</EM>,
GLenum <EM>pname</EM>,
const GLdouble *<EM>params</EM> )
void <STRONG>glTexGenfv</STRONG>( GLenum <EM>coord</EM>,
GLenum <EM>pname</EM>,
const GLfloat *<EM>params</EM> )
void <STRONG>glTexGeniv</STRONG>( GLenum <EM>coord</EM>,
GLenum <EM>pname</EM>,
const GLint *<EM>params</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>coord</EM>
Specifies a texture coordinate. Must be one of <STRONG>GL_S</STRONG>,
<STRONG>GL_T</STRONG>, <STRONG>GL_R</STRONG>, or <STRONG>GL_Q</STRONG>.
<EM>pname</EM>
Specifies the symbolic name of the texture-coordinate
generation function or function parameters. Must be
<STRONG>GL_TEXTURE_GEN_MODE</STRONG>, <STRONG>GL_OBJECT_PLANE</STRONG>, or <STRONG>GL_EYE_PLANE</STRONG>.
<EM>params</EM>
Specifies a pointer to an array of texture generation
parameters. If <EM>pname</EM> is <STRONG>GL_TEXTURE_GEN_MODE</STRONG>, then the
array must contain a single symbolic constant, one of
<STRONG>GL_OBJECT_LINEAR</STRONG>, <STRONG>GL_EYE_LINEAR</STRONG>, or <STRONG>GL_SPHERE_MAP</STRONG>.
Otherwise, <EM>params</EM> holds the coefficients for the
texture-coordinate generation function specified by
<EM>pname</EM>.
<STRONG>DESCRIPTION</STRONG>
<STRONG>glTexGen</STRONG> selects a texture-coordinate generation function or
supplies coefficients for one of the functions. <EM>coord</EM> names
one of the (<EM>s</EM>, <EM>t</EM>, <EM>r</EM>, <EM>q</EM>) texture coordinates; it must be one
of the symbols <STRONG>GL_S</STRONG>, <STRONG>GL_T</STRONG>, <STRONG>GL_R</STRONG>, or <STRONG>GL_Q</STRONG>. <EM>pname</EM> must be one
of three symbolic constants: <STRONG>GL_TEXTURE_GEN_MODE</STRONG>,
<STRONG>GL_OBJECT_PLANE</STRONG>, or <STRONG>GL_EYE_PLANE</STRONG>. If <EM>pname</EM> is
<STRONG>GL_TEXTURE_GEN_MODE</STRONG>, then <EM>params</EM> chooses a mode, one of
<STRONG>GL_OBJECT_LINEAR</STRONG>, <STRONG>GL_EYE_LINEAR</STRONG>, or <STRONG>GL_SPHERE_MAP</STRONG>. If <EM>pname</EM>
is either <STRONG>GL_OBJECT_PLANE</STRONG> or <STRONG>GL_EYE_PLANE</STRONG>, <EM>params</EM> contains
coefficients for the corresponding texture generation
function.
If the texture generation function is <STRONG>GL_OBJECT_LINEAR</STRONG>, 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 <EM>coord</EM>, p , p , p , and p are the four values
supplied in <EM>param</EM><STRONG><</STRONG>EM>s</EM>, a<STRONG>n</STRONG>d x3, y , z4, and w are the object
coordinates of the vertex<STRONG>.</STRONG> T<STRONG>h</STRONG>is <STRONG>f</STRONG>unctionocan 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 <STRONG>i</STRONG>s c<STRONG>o</STRONG>mpu<STRONG>t</STRONG>ed by t<STRONG>h</STRONG>e
<STRONG>GL_OBJECT_LINEAR</STRONG> 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 <STRONG>GL_EYE_LINEAR</STRONG>, 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
verte<STRONG>x</STRONG>, pe, pe, p , a<STRONG>n</STRONG>d p are the values supplied in
<EM>params</EM>, a<STRONG>n</STRONG>d M2is <STRONG>t</STRONG>he mode<STRONG>l</STRONG>view matrix when <STRONG>glTexGen</STRONG> 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 <EM>params</EM> 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 <EM>pname</EM> is <STRONG>GL_SPHERE_MAP</STRONG> and <EM>coord</EM> is either <STRONG>GL_S</STRONG> or <STRONG>GL_T</STRONG>,
s and t texture coordinates are generated as follows. Let <EM>u</EM>
be the unit vector pointing from the origin to the polygon
vertex (in eye coordinates). Let <EM>n</EM> sup prime be the current
normal, after transformation to eye coordinates. Let
f = (f f f )T
be the reflection vector su<STRONG>c</STRONG>h t<STRONG>h</STRONG>at 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 <STRONG>an</STRONG>dxt t<STRONG>e</STRONG>xtur<STRONG>e</STRONG> coordinates are
<STRONG>__</STRONG> <STRONG>_</STRONG>
s = m + 2
f
t = _<STRONG>_</STRONG> + <STRONG>_</STRONG>
m 2
To enable or disable a texture-coordinate generation
function, call <STRONG>glEnable</STRONG> or <STRONG>glDisable</STRONG> with one of the
symbolic texture-coordinate names (<STRONG>GL_TEXTURE_GEN_S</STRONG>,
<STRONG>GL_TEXTURE_GEN_T</STRONG>, <STRONG>GL_TEXTURE_GEN_R</STRONG>, or <STRONG>GL_TEXTURE_GEN_Q</STRONG>) 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 <STRONG>GL_EYE_LINEAR</STRONG> 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).
<STRONG>ERRORS</STRONG>
<STRONG>GL_INVALID_ENUM</STRONG> is generated when <EM>coord</EM> or <EM>pname</EM> is not an
accepted defined value, or when <EM>pname</EM> is <STRONG>GL_TEXTURE_GEN_MODE</STRONG>
and <EM>params</EM> is not an accepted defined value.
<STRONG>GL_INVALID_ENUM</STRONG> is generated when <EM>pname</EM> is
<STRONG>GL_TEXTURE_GEN_MODE</STRONG>, <EM>params</EM> is <STRONG>GL_SPHERE_MAP</STRONG>, and <EM>coord</EM> is
either <STRONG>GL_R</STRONG> or <STRONG>GL_Q</STRONG>.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glTexGen</STRONG> is executed
between the execution of <STRONG>glBegin</STRONG> and the corresponding
execution of <STRONG>glEnd</STRONG>.
<STRONG>ASSOCIATED</STRONG> <STRONG>GETS</STRONG>
<STRONG>glGetTexGen</STRONG>
<STRONG>glIsEnabled</STRONG> with argument <STRONG>GL_TEXTURE_GEN_S</STRONG>
<STRONG>glIsEnabled</STRONG> with argument <STRONG>GL_TEXTURE_GEN_T</STRONG>
<STRONG>glIsEnabled</STRONG> with argument <STRONG>GL_TEXTURE_GEN_R</STRONG>
<STRONG>glIsEnabled</STRONG> with argument <STRONG>GL_TEXTURE_GEN_Q</STRONG>
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>glCopyPixels</STRONG>, <STRONG>glCopyTexImage2D</STRONG>, <STRONG>glCopyTexSubImage1D</STRONG>,
<STRONG>glCopyTexSubImage2D</STRONG>, <STRONG>glTexEnv</STRONG>, <STRONG>glTexImage1D</STRONG>, <STRONG>glTexImage2D</STRONG>,
<STRONG>glTexParameter</STRONG>, <STRONG>glTexSubImage1D</STRONG>, <STRONG>glTexSubImage2D</STRONG>
</PRE>
</BODY>
</HTML>
