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Manual Reference Pages  - GLTEXENV (3G)

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

CONTENTS

C Specification
Parameters
C Specification
Parameters
Description
Notes
Associated Gets
See Also

void glTexEnvf( GLenum target,

              GLenum pname,
              GLfloat param )

void glTexEnvi( GLenum target,

              GLenum pname,
              GLint param )

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.

void glTexEnvfv( GLenum target,

               GLenum pname,
               const GLfloat *params )

void glTexEnviv( GLenum target,

               GLenum pname,
               const GLint *params )

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.

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,  glTexImage3D,  glCopyTexImage1D, and  glCopyTexImage2D). In a one-component image, L_t indicates that single component. A two-component image uses L_t and A_t. A three-component 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 internal	Texture functions
	GL_MODULATE	GL_DECAL	GL_BLEND	GL_REPLACE
GL_ALPHA	Cv = Cf	undefined	Cv = Cf	Cv = Cf
	Av = AfAt		Av = Af	Av = At
GL_LUMINANCE	Cv = LtCf	undefined	Cv = (1-Lt)Cf	Cv = Lt
			+LtCc
1	Av = Af		Av = Af	Av = Af
GL_LUMINANCE	Cv = LtCf	undefined	Cv = (1-Lt)Cf	Cv = Lt
\f3_ALPHA			+LtCc
2	Av = AtAf		Av = AtAf	Av = At
GL_INTENSITY	Cv = CfIt	undefined	Cv = (1-It)Cf	Cv = It
			+ItCc
c	Av = AfIt		Av = (1-It)Af	Av = It
			+ItAc
GL_RGB	Cv = CtCf	Cv = Ct	Cv = (1-Ct)Cf	Cv = Ct
			+CtCc
3	Av = Af	Av = Af	Av = Af	Av = Af
GL_RGBA	Cv = CtCf	Cv = (1-At)Cf	Cv = (1-Ct)Cf	Cv = Ct
		+AtCt	+CtCc
4	Av = AtAf	Av = Af	Av = AtAf	Av = At

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 values.

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

 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 controls the texture environment for the current active texture unit, selected by  glActiveTextureARB.  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.

 glGetTexEnv

 glActiveTextureARB(3G),  glCopyPixels(3G),  glCopyTexImage1D(3G),  glCopyTexImage2D(3G),  glCopyTexSubImage1D(3G),  glCopyTexSubImage2D(3G),  glCopyTexSubImage3D(3G),  glTexImage1D(3G),  glTexImage2D(3G),  glTexImage3D(3G),  glTexParameter(3G),  glTexSubImage1D(3G),  glTexSubImage2D(3G),  glTexSubImage3D(3G)

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