Index for Section 3G

Alphabetical listing for G

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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
  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.

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
  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
  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().

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),
  glCopyTexSubImage1D(3), glCopyTexSubImage2D(3), glCopyTexSubImage3D(3),
  glTexEnv(3), glTexImage1D(3), glTexImage2D(3), glTexImage3D(3), ,
  glTexParameter(3), glTexSubImage1D(3), glTexSubImage2D(3),
  glTexSubImage3D(3)

Index for Section 3G

Alphabetical listing for G

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