glTexEnv man page on DigitalUNIX

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glTexEnv(3G)							  glTexEnv(3G)

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

SYNOPSIS
       void glTexEnvf(
	       GLenum target,
	       GLenum pname,
	       GLfloat param ); void glTexEnvi(
	       GLenum target,
	       GLenum pname,
	       GLint param );

PARAMETERS
       Specifies a texture environment. Must be GL_TEXTURE_ENV.	 Specifies the
       symbolic name of a single-valued texture environment parameter. Must be
       GL_TEXTURE_ENV_MODE.  Specifies a  single  symbolic  constant,  one  of
       GL_MODULATE, GL_DECAL, GL_BLEND, or GL_REPLACE.

SYNOPSIS
       void glTexEnvfv(
	       GLenum target,
	       GLenum pname,
	       const GLfloat *params ); void glTexEnviv(
	       GLenum target,
	       GLenum pname,
	       const GLint *params );

PARAMETERS
       Specifies a texture environment. Must be GL_TEXTURE_ENV.	 Specifies the
       symbolic name of a texture environment parameter. Accepted  values  are
       GL_TEXTURE_ENV_MODE and GL_TEXTURE_ENV_COLOR.  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 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(), glTexImage3D(), glCopyTexImage1D(), and
       glCopyTexImage2D()). In a one-component image, L[t] indicates that sin‐
       gle component. A two-component image uses L[t] and A[t]. A three-compo‐
       nent image has only a color value, C[t].	 A  four-component  image  has
       both a color value C[t] and an alpha value A[t].

       ────────────────────────────────────────────────────────────────────────────
       Base inter‐		      Texture	    Functions
       nal
       format	     GL_MODULATE      GL_DECAL	    GL_BLEND	      GL_REPLACE
       ────────────────────────────────────────────────────────────────────────────
       GL_ALPHA	     C[v]	  =   undefined	    C[v]	  =   C[v]	 =
		     C[f]A[v]	  =		    C[f]A[v] = A[f]   C[f]A[v]	 =
		     A[f] A[t]					      A[t]

       GL_LUMI‐	     C[v]   =  L[t]   undefined	    C[v]  =  (	1 -   C[v]  = L[t]
       NANCE   (or   C[f]  A[v]	  =		    L[t] )  C[f]  +   A[v] = A[f]
       1)	     A[f]			    L[t] C[c]
						     A[v] = A[f]

       GL_LUMI‐	     C[v]  =   L[t]   undefined	    C[v] =  (  1  -   C[v]  = L[t]
       NANCE_ALPHA   C[f]   A[v]  =		    L[t] ) C[f]	      A[v] = A[t]
       (or 2)	     A[t] A[f]			     +	 L[t]  C[c]
						    A[v]   =   A[t]
						    A[f]

       GL_INTEN‐     C[v]   =  C[f]   undefined	    C[v]  =  (	1 -   C[v] =  I[t]
       SITY	     I[t]  A[v]	  =		    I[t] )  C[f]  +   A[v] = I[t]
		     A[f] I[t]			    I[t]  C[c] A[v]
						    = ( 1 - I[t]  )
						    A[f]   +   I[t]
						    A[c]

       GL_RGB  (or   C[v]  =   C[t]   C[v] = C[t]   C[v]   =  (1  -   C[v] =  C[t]
       3)	     C[f]   A[v]  =   A[v] = A[f]   C[t])  C[f]	  +   A[v] = A[f]
		     A[f]			    C[t]  C[c] A[v]
						    = A[f]

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

       ────────────────────────────────────────────────────────────────────────────

       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[c] takes these four  val‐
       ues.

       GL_TEXTURE_ENV_MODE  defaults  to  GL_MODULATE  andGL_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.

       When  the  GL_ARB_multitexture  extension is supported, glTexEnv() con‐
       trols the texture environment for  the  current	active	texture	 unit,
       selected	 byglActiveTextureARB().   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
       glActiveTextureARB(3), glCopyPixels(3), glCopyTexImage1D(3), glCopyTex‐
       Image2D(3), glCopyTexSubImage1D(3), glCopyTexSubImage2D(3),  glCopyTex‐
       SubImage3D(3),  glTexImage1D(3), glTexImage2D(3), glTexImage3D(3), glT‐
       exParameter(3),	glTexSubImage1D(3),  glTexSubImage2D(3),   glTexSubIm‐
       age3D(3)

								  glTexEnv(3G)
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