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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 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 ″ × x e + p 2 ″ × y e + p 3 ″ × z e + p 4 ″ × 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 © 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			  03/16/2013			  GLTEXGEN(3G)

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