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GLTEXGEN(3G)				  OpenGL Manual 			     GLTEXGEN(3G)

NAME
       glTexGen - control the generation of texture coordinates

C SPECIFICATION
       void glTexGeni(GLenum coord, GLenum pname, GLint param);

       void glTexGenf(GLenum coord, GLenum pname, GLfloat param);

       void glTexGend(GLenum coord, GLenum pname, GLdouble 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, GL_SPHERE_MAP, GL_NORMAL_MAP, or GL_REFLECTION_MAP.

C SPECIFICATION
       void glTexGeniv(GLenum coord, GLenum pname, const GLint * params);

       void glTexGenfv(GLenum coord, GLenum pname, const GLfloat * params);

       void glTexGendv(GLenum coord, GLenum pname, const GLdouble * 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, GL_SPHERE_MAP, GL_NORMAL_MAP, or GL_REFLECTION_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, GL_SPHERE_MAP,
       GL_NORMAL_MAP, or GL_REFLECTION_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 x o + p 2 x y o + p 3 x z o + p 4 x 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 '' x x e + p 2 '' x y e + p 3 '' x z e + p 4 '' x w e

       is used, where

       p 1 ''  p 2 ''  p 3 ''  p 4 '' = 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 the texture generation function 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 ''	n '' T	u

       Finally, let m = 2  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 m + 1 2

       t = f y 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 ARB_multitexture extension is supported, glTexGen sets the texture generation
       parameters for the currently active texture unit, selected with glActiveTexture().

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
       glActiveTexture(), glCopyPixels(), glCopyTexImage2D(), glCopyTexSubImage1D(),
       glCopyTexSubImage2D(), glCopyTexSubImage3D(), glTexEnv(), glTexImage1D(), glTexImage2D(),
       glTexImage3D(), glTexParameter(), glTexSubImage1D(), glTexSubImage2D(), glTexSubImage3D()

COPYRIGHT
       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI
       Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.

AUTHORS
       opengl.org

opengl.org				    06/10/2014				     GLTEXGEN(3G)
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