NAME
	  glTexEnvf, glTexEnvi,	glTexEnvfv, glTexEnviv - set texture
	  environment parameters


     C SPECIFICATION
	  void glTexEnvf( GLenum target,
			  GLenum pname,
			  GLfloat param	)
	  void glTexEnvi( GLenum target,
			  GLenum pname,
			  GLint	param )


     PARAMETERS
	  target  Specifies a texture environment.  Must be
		  GL_TEXTURE_ENV.

	  pname	  Specifies the	symbolic name of a single-valued
		  texture environment parameter.  Must be
		  GL_TEXTURE_ENV_MODE.

	  param	  Specifies a single symbolic constant,	one of
		  GL_MODULATE, GL_DECAL, GL_BLEND, or GL_REPLACE.

     C SPECIFICATION
	  void glTexEnvfv( GLenum target,
			   GLenum pname,
			   const GLfloat *params )
	  void glTexEnviv( GLenum target,
			   GLenum pname,
			   const GLint *params )


     PARAMETERS
	  target
	       Specifies a texture environment.	 Must be
	       GL_TEXTURE_ENV.

	  pname
	       Specifies the symbolic name of a	texture	environment
	       parameter.  Accepted values are GL_TEXTURE_ENV_MODE and
	       GL_TEXTURE_ENV_COLOR.

	  params
	       Specifies a pointer to a	parameter array	that contains
	       either a	single symbolic	constant or an RGBA color.

     DESCRIPTION
	  A texture environment	specifies how texture values are
	  interpreted when a fragment is textured.  target must	be
	  GL_TEXTURE_ENV.  pname can be	either GL_TEXTURE_ENV_MODE or
	  GL_TEXTURE_ENV_COLOR.

	  If pname is GL_TEXTURE_ENV_MODE, then	params is (or points
	  to) the symbolic name	of a texture function.	Four texture
	  functions may	be specified:  GL_MODULATE, GL_DECAL,
	  GL_BLEND, and	GL_REPLACE.

	  A texture function acts on the fragment to be	textured using
	  the texture image value that applies to the fragment (see
	  glTexParameter) and produces an RGBA color for that
	  fragment.  The following table shows how the RGBA color is
	  produced for each of the three texture functions that	can be
	  chosen.  C is	a triple of color values (RGB) and A is	the
	  associated alpha value.  RGBA	values extracted from a
	  texture image	are in the range [0,1].	 The subscript f
	  refers to the	incoming fragment, the subscript t to the
	  texture image, the subscript c to the	texture	environment
	  color, and subscript v indicates a value produced by the
	  texture function.

	  A texture image can have up to four components per texture
	  element (see glTexImage1D, glTexImage2D, glCopyTexImage1D,
	  and glCopyTexImage2D). In a one-component image, L
	  indicates that single	component.  A two-component image uses
	  L  and A .  A	three-component	image has only a color value,
	  Ct.  A four-component	image has both a color value C	and an
	  alpha	value A	.				      t
		       t
























     _______________________________________________________________________
     |Base internal ||		    Texture functions			    |
     |	 format	    ||GL_MODULATE    GL_DECAL	    GL_BLEND	 GL_REPLACE |
     |______________||______________________________________________________|
     |	GL_ALPHA    ||	 C =C	  |		|    C =C      |   C =C	    |
     |		    ||	A =A A	  |  undefined	|    Av=Af     |   Av=Af    |
     |______________||____________|_____________|______________|____________|
     |GL_LUMINANCE  ||	C =L C	  |  undefined	| C =(1-L )C   |   C =L	    |
     |	    1	    ||	 v  t f	  |		|  v +L	Ct  f  |    v  t    |
     |		    ||		  |		|      t c     |	    |
     |		    ||	 A =A	  |		|     A	=A     |   A =A	    |
     |______________||____________|_____________|______________|____________|
     |GL_LUMINANCE  ||	C =L C	  |  undefined	| C =(1-L )C   |   C =L	    |
     |	 _ALPHA	    ||	 v  t f	  |		|  v  +L C  f  |    v  t    |
     |	    2	    ||		  |		|	t c    |	    |
     |		    ||	A =A A	  |		|   A =A A     |   A =A	    |
     |______________||____________|_____________|______________|____________|
     |GL_INTENSITY  ||	C =C I	  |  undefined	| C =(1-I )C   |   C =I	    |
     |		    ||	 v  f t	  |		|  v +I	Ct  f  |    v  t    |
     |		    ||		  |		|      t c     |	    |
     |		    ||	A =A I	  |		| A =(1-I )A   |   A =I	    |
     |		    ||	 v  f t	  |		|  v +I	At  f  |    v  t    |
     |______________||____________|_____________|______________|____________|
     |	 GL_RGB	    ||	C =C C	  |    C =C	| C =(1-C  C   |   C =C	    |
     |	    3	    ||	 v  t f	  |	v  t	|  v  +C C) f  |    v  t    |
     |		    ||		  |		|	t c    |	    |
     |		    ||	 A =A	  |    A =A	|    A =A      |   A =A	    |
     |______________||____________|_____________|______________|____________|
     |	 GL_RGBA    ||	C =C C	  | C =(1-A )C	| C =(1-C  C   |   C =C	    |
     |	    4	    ||	 v  t f	  |  v +A Ct  f	|  v  +C C) f  |    v  t    |
     |		    ||		  |	 t t	|	t c    |	    |
     |		    ||	A =A A	  |    A =A	|   A =A A     |   A =A	    |
     |______________||____________||_____________||______________||____________|

	  If pname is GL_TEXTURE_ENV_COLOR, params is a	pointer	to an
	  array	that holds an RGBA color consisting of four values.
	  Integer color	components are interpreted linearly such that
	  the most positive integer maps to 1.0, and the most negative
	  integer maps to -1.0.	 The values are	clamped	to the range
	  [0,1]	when they are specified.  C  takes these four values.
					   c
	  GL_TEXTURE_ENV_MODE defaults to GL_MODULATE and
	  GL_TEXTURE_ENV_COLOR defaults	to (0, 0, 0, 0).

     NOTES
	  GL_REPLACE may only be used if the GL	version	is 1.1 or
	  greater.

	  Internal formats other than 1, 2, 3, or 4 may	only be	used
	  if the GL version is 1.1 or greater.

     ERRORS

	  GL_INVALID_ENUM is generated when target or pname is not one
	  of the accepted defined values, or when params should	have a
	  defined constant value (based	on the value of	pname) and
	  does not.

	  GL_INVALID_OPERATION is generated if glTexEnv	is executed
	  between the execution	of glBegin and the corresponding
	  execution of glEnd.

     ASSOCIATED	GETS
	  glGetTexEnv

     SEE ALSO
	  glCopyPixels,	glCopyTexImage1D, glCopyTexImage2D,
	  glCopyTexSubImage1D, glCopyTexSubImage2D, glTexImage1D,
	  glTexImage2D,	glTexParameter,	glTexSubImage1D,
	  glTexSubImage2D