GLTEXGEN(3G)															      GLTEXGEN(3G)

NAME

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

C SPECIFICATION

       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.

C SPECIFICATION

       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 = p1xo + p2yo + p3zo + p4wo

       is used, where g is the value computed for the coordinate named in coord, p1, p2, p3 and p4 are the four values supplied in params, and xo,
       yo, zo, and wo 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 p1, p2, p3, and p4).  The altitude of a terrain vertex is computed by the GL_OBJECT_LINEAR coordinate genera-
       tion  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 = p1'xe + p2'ye + p3'ze + p4'we

       is used, where

							 (p1' p2' p3' p4') = (p1 p2 p3 p4) M^-1

       and xe, ye, ze, and we are the eye coordinates of the vertex, p1, p2, p3, and p4 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 = (fx fy fz)^T

       be the reflection vector such that

								   f = u - 2 n' n'^T u

       Finally, let m = 2 sqrt( fx^2 + fy^2 + (fz + 1)^2). Then the values assigned to the s and t texture coordinates are

								   s = (fx/m) + (1/2)

								   t = (fy/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 coordi-
       nate is computed according to the generating function associated with that coordinate.  When disabled, subsequent vertices take the  speci-
       fied  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,  glCopyPixels, glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubImage2D, glCopyTexSubImage3D, glTexEnv, glTexImage1D,
       glTexImage2D, glTexImage3D, glTexParameter, glTexSubImage1D, glTexSubImage2D, glTexSubImage3D

																      GLTEXGEN(3G)