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glTexEnv
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glTexEnvf, glTexEnvi, glTexEnvfv, glTexEnviv: set texture environment parameters.

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

[Up] C Specification

void glTexEnvf(
    GLenum	  target,
    GLenum	  pname,
    GLfloat	  param)
void glTexEnvi(
    GLenum	  target,
    GLenum	  pname,
    GLint	  param)
void glTexEnvfv(
    GLenum	  target,
    GLenum	  pname,
    const GLfloat *params) 
void glTexEnviv(
    GLenum	  target,
    GLenum	  pname,
    const GLint   *params) 

[Up] Parameters

target
Specifies a texture environment. Must be GL_TEXTURE_ENV.
pname (for glTexEnvf and glTexEnvi)
Specifies the symbolic name of a single-valued texture environment parameter. Must be GL_TEXTURE_ENV_MODE.
pname (for glTexEnvfv and glTexEnviv)
Specifies the symbolic name of a texture environment parameter. Accepted values are GL_TEXTURE_ENV_MODE and GL_TEXTURE_ENV_COLOR and GL_TEXTURE_LIGHTING_MODE_HP.
param
Specifies a single symbolic constant, one of GL_MODULATE, GL_DECAL, GL_BLEND, or GL_REPLACE. If pname is GL_TEXTURE_LIGHTING_MODE_HP, specifies a single symbolic constant, either GL_TEXTURE_POST_SPECULAR_HP or GL_TEXTURE_PRE_SPECULAR_HP.
params
Specifies a pointer to a parameter array that contains either a single symbolic constant or an RGBA color.

[Up] 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, GL_TEXTURE_ENV_COLOR or GL_TEXTURE_LIGHTING_MODE_HP (if the extension GL_HP_texture_lighting is supported).

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. If pname is GL_TEXTURE_LIGHTING_MODE_HP, two possible values for param may be specified: either GL_TEXTURE_PRE_SPECULAR_HP or GL_TEXTURE_POST_SPECULAR_HP.

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, glCopyTexImage1D, and glCopyTexImage2D). 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.

Base Internal
Format
Texture Functions
GL_MODULATE GL_DECAL GL_BLEND GL_REPLACE
GL_ALPHA Cv = Cf (undefined ) Cv = Cf Cv = Cf
Av = Af At Av = Af Av = At
GL_LUMINANCE
1
Cv = Lt Cf (undefined ) Cv = (1 - Lt ) Cf + Lt Cc Cv = Lt
Av = Af Av = Af Av = Af
GL_LUMINANCE_ALPHA
2
Cv = Lt Cf (undefined ) Cv = (1 - Lt ) Cf + Lt Cc Cv = Lt
Av = At Af Av = At Af Av = At
GL_INTENSITY Cv = Cf It (undefined ) Cv = (1 - It ) Cf + It Cc Cv = It
Av = Af It Av = (1 - It ) Af + It Ac Av = It
GL_RGB
3
Cv = Ct Cf Cv = Ct Cv = (1 - Ct ) Cf + Ct Cc Cv = Ct
Av = Af Av = Af Av = Af Av = Af
GL_RGBA
4
Cv = Ct Cf Cv = (1 - At ) Cf + At Ct Cv = (1 - Ct ) Cf + Ct Cc Cv = Ct
Av = At Af Av = Af Av = At Af 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. Cc takes these four values.

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

[Up] Notes

GL_REPLACE may only be used if the GL version is 1.1 or greater.

GL_TEXTURE_LIGHTING_MODE_HP may only be used if the GL_HP_texture_lighting extension is supported.

Internal formats other than 1, 2, 3, or 4 may only be used if the GL version is 1.1 or greater.

[Up] Errors

[Up] Associated Gets

glGetTexEnv

[Up] See Also

glCopyPixels,
glCopyTexImage1D,
glCopyTexImage2D,
glCopyTexSubImage1D,
glCopyTexSubImage2D,
glTexImage1D,
glTexImage2D,
glTexParameter,
glTexSubImage1D,
glTexSubImage2D

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