glTexEnv

NAME

C SPECIFICATION

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

PARAMETERS

C SPECIFICATION

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

PARAMETERS

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.

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. 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 and an alpha value A_t.

Base InternalFormat	GL_MODULATE	GL_DECAL	GL_BLEND	GL_REPLACE
GL_ALPHA	Cv = Cf Av = AtAf	undefined	Cv = Cf Av = AtAf	Cv = Cf Av = At
GL_LUMINANCE (1)	Cv = LtCf Av = Af	undefined	Cv = (1 - Lt)Cf + LtCc Av = Af	Cv = Lt Av = Af
GL_LUMINANCE_ALPHA (2)	Cv = LtCf Av = AtAf	undefined	Cv = (1 - Lt)Cf + LtCc Av = AtAf	Cv = Lt Av = At
GL_INTENSITY	Cv = ItCf Av = ItAf	undefined	Cv = (1 - It)Cf + ItCc Av = ItAf	Cv = It Av = It
GL_RGB (3)	Cv = CtCf Av = Af	Cv = Ct Av = Af	Cv = (1 - Ct)Cf + CtCc Av = Af	Cv = Ct Av = Af
GL_RGBA (4)	Cv = CtCf Av = AtAf	Cv = (1 - At)Cf + AtCt Av = Af	Cv = (1 - Ct)Cf + CtCc Av = AtAf	Cv = Ct 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).

NOTES

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_OPERATION is generated if glTexEnv is executed between the execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS

SEE ALSO