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GLTEXENV()							    GLTEXENV()

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 )

       delim $$

PARAMETERS
       target  Specifies a texture environment.	 Must be GL_TEXTURE_ENV.

       pname   Specifies the symbolic name of a	single-valued texture environ-
	       ment 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_TEX-
	      TURE_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 sym-
       bolic name of a texture function.  Four texture functions may be	speci-
       fied: GL_MODULATE, GL_DECAL, GL_BLEND, and GL_REPLACE.

       A  texture  function acts on the	fragment to be textured	using the tex-
       ture 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 frag-
       ment, 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, $L sub	t$ indicates that single component.  A
       two-component image uses	$L sub t$ and $A sub  t$.   A  three-component
       image  has  only	 a color value,	$C sub t$.  A four-component image has
       both a color value $C sub t$ and	an alpha value $A sub t$.

+---------------++--------------------------------------------------------------------------------------------------------------------------------+
| Base internal	||						     Texture functions								  |
|    format	||	  GL_MODULATE			      GL_DECAL				     GL_BLEND			  GL_REPLACE	  |
+---------------++----------------------------+--------------------------------------+--------------------------------------+---------------------+
|   GL_ALPHA	||    $C sub v = C sub f$     |		     undefined		     |	       $C sub v	=  C sub f$	    | $C sub v = C sub f$ |
|		||$A sub v = A sub f A sub t$ |					     |	       $A sub v	= A sub	f$	    | $A sub v = A sub t$ |
+---------------++----------------------------+--------------------------------------+--------------------------------------+---------------------+
| GL_LUMINANCE	||$C sub v = L sub t C sub f$ |		     undefined		     | $C sub v	= ( 1 -	L sub t	) C sub	f$  | $C sub v = L sub t$ |
|	1	||			      |					     |	       $+ L sub	t C sub	c$	    |			  |
|		||			      |					     |					    |			  |
|		||    $A sub v = A sub f$     |					     |		$A sub v = A sub f$	    | $A sub v = A sub f$ |
+---------------++----------------------------+--------------------------------------+--------------------------------------+---------------------+
| GL_LUMINANCE	||$C sub v = L sub t C sub f$ |		     undefined		     | $C sub v	= ( 1 -	L sub t	) C sub	f $ | $C sub v = L sub t$ |
|   \f3_ALPHA	||			      |					     |		$+ L sub t C sub c$	    |			  |
|	2	||			      |					     |					    |			  |
|		||$A sub v = A sub t A sub f$ |					     |	   $A sub v = A	sub t A	sub f$	    | $A sub v = A sub t$ |
+---------------++----------------------------+--------------------------------------+--------------------------------------+---------------------+
| GL_INTENSITY	||$C sub v = C sub f I sub t$ |		     undefined		     | $C sub v	= ( 1 -	I sub t	) C sub	f$  | $C sub v = I sub t$ |
|		||			      |					     |	       $+ I sub	t C sub	c$	    |			  |
|		||			      |					     |					    |			  |
|		||$A sub v = A sub f I sub t$ |					     | $A sub v	= ( 1 -	I sub t	) A sub	f $ | $A sub v = I sub t$ |
|		||			      |					     |	       $+ I sub	t A sub	c$	    |			  |
+---------------++----------------------------+--------------------------------------+--------------------------------------+---------------------+
|    GL_RGB	||$C sub v = C sub t C sub f$ |		$C sub v = C sub t$	     |	$C sub v = (1 -	C sub t) C sub f $  | $C sub v = C sub t$ |
|	3	||			      |					     |		$+ C sub t C sub c$	    |			  |
|		||			      |					     |					    |			  |
|		||    $A sub v = A sub f$     |		$A sub v = A sub f$	     |	       $A sub v	= A sub	f$	    | $A sub v = A sub f$ |
+---------------++----------------------------+--------------------------------------+--------------------------------------+---------------------+
|    GL_RGBA	||$C sub v = C sub t C sub f$ |	$C sub v = ( 1 - A sub t ) C sub f $ |	$C sub v = (1 -	C sub t) C sub f $  | $C sub v = C sub t$ |
|	4	||			      |		$+ A sub t C sub t$	     |		$+ C sub t C sub c$	    |			  |
|		||			      |					     |					    |			  |
|		||$A sub v = A sub t A sub f$ |		$A sub v = A sub f$	     |	   $A sub v = A	sub t A	sub f$	    | $A sub v = A sub t$ |
+---------------++----------------------------+--------------------------------------+--------------------------------------+---------------------+

       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	compo-
       nents 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.  $C sub c$ takes
       these four values.

       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 ac-
       cepted 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,	glTex-
       SubImage1D, glTexSubImage2D

								    GLTEXENV()

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