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fglTexEnv(3G)		       OpenGL Reference			 fglTexEnv(3G)

NAME
     fglTexEnvf, fglTexEnvi, fglTexEnvfv, fglTexEnviv - set texture
     environment parameters

FORTRAN SPECIFICATION
     SUBROUTINE fglTexEnvf( INTEGER*4 target,
			    INTEGER*4 pname,
			    REAL*4 param )
     SUBROUTINE fglTexEnvi( INTEGER*4 target,
			    INTEGER*4 pname,
			    INTEGER*4 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, GL_REPLACE, GL_REPLACE_EXT, or GL_ADD.

FORTRAN SPECIFICATION
     SUBROUTINE fglTexEnvfv( INTEGER*4 target,
			     INTEGER*4 pname,
			     CHARACTER*8 params )
     SUBROUTINE fglTexEnviv( INTEGER*4 target,
			     INTEGER*4 pname,
			     CHARACTER*8 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, GL_TEXTURE_ENV_COLOR, and
	  GL_TEXTURE_ENV_BIAS_SGIX.

     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
     GL_TEXTURE_ENV_MODE, GL_TEXTURE_ENV_COLOR, or GL_TEXTURE_ENV_BIAS_SGIX.

									Page 1

fglTexEnv(3G)		       OpenGL Reference			 fglTexEnv(3G)

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

     A texture function acts on the fragment to be textured using the texture
     image value that applies to the fragment (see fglTexParameter) and
     produces an RGBA color for that fragment.	The following tables show how
     the RGBA color is produced for each of the texture functions.  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, the
     subscript b to the texture environment bias 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
     fglTexImage1D and fglTexImage2D).	In an image of GL_LUMINANCE format L
									    t
     indicates the single component.  In an image of GL_ALPHA format A
								      t
     indicates the single component.  In an image of GL_INTENSITY format I
									  t
     indicates the single component.  A two-component image uses L  and A .  A
								  t	 t
     three-component image has only a color value, C .	A four-component image
						    t
     has both a color value C  and an alpha value A .
			     t			   t

	  number of		       texture functions
	  components	   GL_MODULATE	     GL_DECAL		GL_BLEND
      ______________________________________________________________________
	 GL_LUMINANCE	     C =L C			    C =(1-L )C +L C
			      v	 t f			     v	   t  f	 t c
	      1		      A =A	    undefined		 A =A
			       v  f				  v  f
      ______________________________________________________________________

	   GL_ALPHA	      C =C				 C =C
			       v  f				  v  f
			     A =A A	    undefined		A =A A
			      v	 t f				 v  t f
      ______________________________________________________________________

	 GL_INTENSITY	     C =I C			    C =(1-I )C +I C
			      v	 t f			     v	   t  f	 t c
			     A =I A	    undefined	    A =(1-I )A +I A
			      v	 t f			     v	   t  f	 t c
      ______________________________________________________________________

      GL_LUMINANCE_ALPHA     C =L C			    C =(1-L )C +L C
			      v	 t f			     v	   t  f	 t c
	      2		     A =A A	    undefined		A =A A
			      v	 t f				 v  t f
      ______________________________________________________________________

	    GL_RGB	     C =C C	      C =C	    C =(1-C )C +C C
			      v	 t f	       v  t	     v	   t  f	 t c
	      3		      A =A	      A =A		 A =A
			       v  f	       v  f		  v  f
      ______________________________________________________________________

	   GL_RGBA	     C =C C	 C =(1-A )C +A C    C =(1-C )C +C C
			      v	 t f	  v	t  f  t t    v	   t  f	 t c
	      4		     A =A A	      A =A		A =A A
			      v	 t f	       v  f		 v  t f

									Page 2

fglTexEnv(3G)		       OpenGL Reference			 fglTexEnv(3G)

	    number of		       texture functions
	    components	     GL_REPLACE_EXT   GL_ADD (SGIX)   GL_ADD (EXT)
	__________________________________________________________________
	   GL_LUMINANCE		 C =L	      C =C +L C +C	C =C +L
				  v  t	       v  f  t c  b	 v  f  t
		1		 A =A		  A =A		 A =A
				  v  f		   v  f		  v  f
	__________________________________________________________________

	     GL_ALPHA		 C =C		  C =C		 C =C
				  v  f		   v  f		  v  f
				 A =A		 A =A A		A =A A
				  v  t		  v  t f	 v  f t
	__________________________________________________________________

	   GL_INTENSITY		 C =I	      C =C +I C +C	C =C +I
				  v  t	       v  f  t c  b	 v  f  t
				 A =I	      A =A +I A +A	A =A +I
				  v  t	       v  f  t c  b	 v  f  t
	__________________________________________________________________

	GL_LUMINANCE_ALPHA	 C =L	      C =C +L C +C	C =C +L
				  v  t	       v  f  t c  b	 v  f  t
		2		 A =A		 A =A A		A =A A
				  v  t		  v  t f	 v  f t
	__________________________________________________________________

	      GL_RGB		 C =C	      C =C +C C +C	C =C +C
				  v  t	       v  f  t c  b	 v  f  t
		3		 A =A		  A =A		 A =A
				  v  f		   v  f		  v  f
	__________________________________________________________________

	     GL_RGBA		 C =C	      C =C +C C +C	C =C +C
				  v  t	       v  f  t c  b	 v  f  t
		4		 A =A		 A =A A		A =A A
				  v  t		  v  t f	 v  f t

									Page 3

fglTexEnv(3G)		       OpenGL Reference			 fglTexEnv(3G)

     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

     If pname is GL_TEXTURE_ENV_BIAS_SGIX, 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
							   b
     values.

     GL_TEXTURE_ENV_MODE defaults to GL_MODULATE, GL_TEXTURE_ENV_COLOR
     defaults to (0,0,0,0), and GL_TEXTURE_ENV_BIAS_SGIX defaults to
     (0,0,0,0).

NOTES
     GL_REPLACE may only be used if the GL version is 1.1 or greater.
     GL_REPLACE_EXT is part of the EXT_texture extension.  GL_ADD and is part
     of both the SGIX_texture_add_env and EXT_texture_env_env extensions
     although the texture function it enables differs between the two
     extensions.  GL_TEXTURE_ENV_BIAS_SGIX is part of the SGIX_texture_add_env
     extension.	 See fglIntro for more information concerning extensions.

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 fglTexEnv is executed between the
     execution of fglBegin and the corresponding execution of fglEnd.

ASSOCIATED GETS
     fglGetTexEnv

MACHINE DEPENDENCIES
     RealityEngine, RealityEngine2, and VTX and High Impact and Maximum Impact
     systems do not support GL_REPLACE_EXT.

     With High Impact and Maximum Impact on Indigo2 systems, the GL_BLEND mode
     is supported for GL_LUMINANCE and GL_LUMINANCE_ALPHA textures only. High
     Impact and Maximum Impact on Octane systems supports all but GL_RGBA.
     Specifying this mode for the unsupported texture formats will result in
     texture-mapping being effectively disabled.

     The SGIX_texture_add_env extension is supported only on InfiniteReality
     systems.  There is a significant restriction on the texture environment
     bias color, however.  Only two values are allowed for the bias:  zero, or
     exactly -0.5 times the texture environment color.	(This makes the
     expression C C +C	equivalent to C C  or (C -0.5)C , respectively.)
		 t c  b		       t c	t      c

									Page 4

fglTexEnv(3G)		       OpenGL Reference			 fglTexEnv(3G)

     Please note that this extension is not the same as the
     EXT_texture_env_add extension despite the potentially confusing
     similarity between names.

     The EXT_texture_env_add extension is supported only on Octane2 VPro
     systems.  Please note that it is not the same as the SGIX_texture_add_env
     extension despite the potentially confusing similarity between names.

SEE ALSO
     fglCopyPixels, fglCopyTexImage1D, fglCopyTexImage2D,
     fglCopyTexSubImage1D, fglCopyTexSubImage2D, fglCopyTexSubImage3D,
     fglTexImage1D, fglTexImage2D, fglTexImage3D, fglTexParameter,
     fglTexSubImage1D, fglTexSubImage2D, fglTexSubImage3D

									Page 5

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