glTexGen man page on DigitalUNIX

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glTexGen(3G)							  glTexGen(3G)

NAME
       glTexGen,  glTexGend,  glTexGenf,  glTexGeni,  glTexGendv,  glTexGenfv,
       glTexGeniv - control the generation of texture coordinates

SYNOPSIS
       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
       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  tex‐
       ture  generation	 parameter, one of GL_OBJECT_LINEAR, GL_EYE_LINEAR, or
       GL_SPHERE_MAP.

SYNOPSIS
       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
       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 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_TEX‐
       TURE_GEN_MODE, GL_OBJECT_PLANE, or GL_EYE_PLANE.	 If pname  is  GL_TEX‐
       TURE_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 tex‐
       ture 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 ter‐
       rain 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 condi‐
       tioned 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 coordi‐
       nates. 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 val‐
       ues 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_TEX‐
       TURE_GEN_Q) as the argument. When enabled, the specified texture	 coor‐
       dinate 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. Ini‐
       tially, 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.

       GL_INVALID_OPERATION is generated if glTexGen() is executed between the
       execution of glBegin() and the corresponding execution 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(3), glCopyPixels(3), glCopyTexImage2D(3), glCopyTex‐
       SubImage1D(3), glCopyTexSubImage2D(3),  glCopyTexSubImage3D(3),	glTex‐
       Env(3),	glTexImage1D(3),  glTexImage2D(3), glTexImage3D(3), , glTexPa‐
       rameter(3), glTexSubImage1D(3), glTexSubImage2D(3), glTexSubImage3D(3)

								  glTexGen(3G)
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