glTexEnv Subroutine

OpenGL 1.1 for AIX: Reference Manual

glTexEnv Subroutine

Purpose

Sets texture environment parameters.

Library

OpenGL C bindings library: libGL.a

C Syntax

void glTexEnvf(GLenum Target, 
   GLenum pName,
   GLfloat Parameter)

void glTexEnvi(GLenum Target, 
   GLenum pName,
   GLint Parameter)

void glTexEnvfv(GLenum Target, 
     GLenum pName,
     const GLfloat *Parameters)

void glTexEnviv(GLenum Target, 
    GLenum pName,
    const GLint *Parameters)

Parameters

glTexEnvf or glTexEnvi

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

glTexEnvfv or glTexEnviv

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.
Parameters	Specifies a pointer to an array of parameters: either a single symbolic constant or an RGBA color.

Description

A texture environment specifies how texture values are interpreted when a fragment is textured. The Target parameter must be GL_TEXTURE_ENV. The pName parameter can be either GL_TEXTURE_ENV_MODE or GL_TEXTURE_ENV_COLOR.

If the pName parameter is GL_TEXTURE_ENV_MODE, the Parameters parameter is (or points to) the symbolic name of a texture function. Three texture functions are defined: GL_MODULATE, GL_DECAL, GL_BLEND, or GL_REPLACE.

A texture function acts on the fragment to be textured using the texture image value that applies to the fragment and produces a red, green, blue, alpha (RGBA) color for that fragment. (See the glTexParameter subroutine for details on setting texture parameters.) The following table shows how the RGBA color is produced for each of the four 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 the glTexImage1D subroutine, the glTexImage2D subroutine, and the glTexImage3DEXT subroutine.) In a one-component image, Lt indicates that single component. A two-component image uses Lt and At. A three-component image has only a color value, Ct. A four-component image has both a color value, Ct, and an alpha value, At.

Note: In the following table, "It" equals the texture intensity.

	Texture Functions
Internal Formats	GL_MODULATE	GL_DECAL	GL_BLEND	GL_REPLACE
GL_LUMINANCE or 1	Cv=LtCf Av=Af	undefined	Cv=(1-Lt) Cf+LtCc Av=Af	Cv=Lt Av=Af
GL_LUMINANCE_ALPHA or 2	Cv=LtCf Av=AtAf	undefined	Cv=(1-Lt) Cf+LtCc Av=AtAf	Cv=Lt Av=At
GL_RGB or 3	Cv=CtCf Av=Af	Cv=Ct Av=Af	Cv=(1-Ct) Cf+CtCc Av=Af	Cv=Ct Av=Af
GL_RGB or 4	Cv=CtCf Av=AtAf	Cv=(1-At) Cf+AtCt Av=Af	Cv=(1-Ct) Cf+CtCc Av=AtAf	Cv=Ct Av=At
GL_INTENSITY	Cv=ItCf Av=ItAf	undefined	Cv=(1-It) Cf+ItCc Av=(1-It) Af+ItAc	Cv=It Av=It
GL_ALPHA	Cv=Cf Av=AtAf	undefined	Cv=Cf Av=AtAf	Cv=Cf Av=At

If the pName parameter is GL_TEXTURE_ENV_COLOR, the Parameters parameter 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. Cc takes these four values.

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

Error Codes

GL_INVALID_ENUM	Target or pName is not one of the accepted defined values, or Parameters should have a defined constant value (based on the value of pName) and does not.
GL_INVALID_OPERATION	The glTexEnv subroutine is called between a call to glBegin and the corresponding call to glEnd.

Associated Gets

Associated gets for the glTexEnv subroutine are as follows. (See the glGet subroutine for more information.)

glGetTexEnv.

Files

/usr/include/GL/gl.h

Contains C language constants, variable type definitions, and ANSI function prototypes for OpenGL.

Related Information

The glBegin or glEnd subroutine, glGetTexEnv subroutine, glTexImage1D subroutine, glTexImage2D subroutine, glTexParameter subroutine.

OpenGL Overview.