glTexEnv

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) 

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.

Description

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, 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 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. 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_TEXTURE_LIGHTING_HP defaults to GL_TEXTURE_POST_SPECULAR_HP.

Notes

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.

Errors

• 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

See Also