glTexEnv(3G)
glTexEnvf, glTexEnvi, glTexEnvfv, glTexEnviv - set texture environment parameters
As shipped in IRIX 6.5. First release of IRIX 6.5.
NAME glTexEnvf, glTexEnvi, glTexEnvfv, glTexEnviv - set texture environment parameters C SPECIFICATION void glTexEnvf( GLenum target, GLenum pname, GLfloat param ) void glTexEnvi( GLenum target, GLenum pname, GLint param ) PARAMETERS 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, GL_REPLACE, GL_REPLACE_EXT, or GL_ADD. C SPECIFICATION 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 Specifies the symbolic name of a texture environment parameter. Accepted values are GL_TEXTURE_ENV_MODE, GL_TEXTURE_ENV_COLOR, and GL_TEXTURE_ENV_BIAS_SGIX. params Specifies a pointer to a parameter array that contains either a single symbolic constant or an RGBA color. DESCRIPTION A texture environment specifies how texture values are interpreted when a fragment is textured. target must be GL_TEXTURE_ENV. pname can be GL_TEXTURE_ENV_MODE, GL_TEXTURE_ENV_COLOR, or GL_TEXTURE_ENV_BIAS_SGIX. If pname is GL_TEXTURE_ENV_MODE, then params is (or points to) the symbolic name of a texture function. Six texture functions may be defined: GL_MODULATE, GL_DECAL, GL_BLEND, GL_REPLACE, GL_REPLACE_EXT, and GL_ADD. 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 tables show how the RGBA color is produced for each of the texture functions. 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, the subscript b to the texture environment bias 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 and glTexImage2D). In an image of GL_LUMINANCE format L t indicates the single component. In an image of GL_ALPHA format A t indicates the single component. In an image of GL_INTENSITY format I t indicates the single component. A two-component image uses L and A . A t t three-component image has only a color value, C . A four-component image t has both a color value C and an alpha value A . If a color triple is t t shown to be equal to a single component format, this denotes that each component of the color triple is set equal to the single component. Similarly when 2 color triples are shown as being multiplied, this denotes that each component of the first triple is multiplied by the corresponding component of the second triple. number of texture functions components GL_MODULATE GL_DECAL GL_BLEND ______________________________________________________________________ GL_LUMINANCE C =L C C =(1-L )C +L C v t f v t f t c 1 A =A undefined A =A v f v f ______________________________________________________________________ GL_ALPHA C =C C =C v f v f A =A A undefined A =A A v t f v t f ______________________________________________________________________ GL_INTENSITY C =I C C =(1-I )C +I C v t f v t f t c A =I A undefined A =(1-I )A +I A v t f v t f t c ______________________________________________________________________ GL_LUMINANCE_ALPHA C =L C C =(1-L )C +L C v t f v t f t c 2 A =A A undefined A =A A v t f v t f ______________________________________________________________________ GL_RGB C =C C C =C C =(1-C )C +C C v t f v t v t f t c 3 A =A A =A A =A v f v f v f ______________________________________________________________________ GL_RGBA C =C C C =(1-A )C +A C C =(1-C )C +C C v t f v t f t t v t f t c 4 A =A A A =A A =A A v t f v f v t f number of texture functions components GL_REPLACE_EXT GL_ADD ___________________________________________________ GL_LUMINANCE C =L C =C +L C +C v t v f t c b 1 A =A A =A v f v f ___________________________________________________ GL_ALPHA C =C C =C v f v f A =A A =A A v t v t f ___________________________________________________ GL_INTENSITY C =I C =C +I C +C v t v f t c b A =I A =A +I A +A v t v f t c b ___________________________________________________ GL_LUMINANCE_ALPHA C =L C =C +L C +C v t v f t c b 2 A =A A =A A v t v t f ___________________________________________________ GL_RGB C =C C =C +C C +C v t v f t c b 3 A =A A =A v f v f ___________________________________________________ GL_RGBA C =C C =C +C C +C v t v f t c b 4 A =A A =A A v t v t f 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 takes these four values. c If pname is GL_TEXTURE_ENV_BIAS_SGIX, 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 takes these four b values. GL_TEXTURE_ENV_MODE defaults to GL_MODULATE, GL_TEXTURE_ENV_COLOR defaults to (0,0,0,0), and GL_TEXTURE_ENV_BIAS_SGIX defaults to (0,0,0,0). NOTES GL_REPLACE may only be used if the GL version is 1.1 or greater. GL_REPLACE_EXT is part of the EXT_texture extension. GL_ADD and GL_TEXTURE_ENV_BIAS_SGIX are part of the SGIX_texture_add_env extension. See glIntro for more information concerning extensions. 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 glGetTexEnv MACHINE DEPENDENCIES RealityEngine, RealityEngine2, and VTX and High Impact and Maximum Impact systems do not support GL_REPLACE_EXT. With High Impact and Maximum Impact on Indigo2 systems, the GL_BLEND mode is supported for GL_LUMINANCE and GL_LUMINANCE_ALPHA textures only. High Impact and Maximum Impact on Octane systems supports all but GL_RGBA. Specifying this mode for the unsupported texture formats will result in texture-mapping being effectively disabled. The SGIX_texture_add_env extension is supported only on InfiniteReality systems. There is a significant restriction on the texture environment bias color, however. Only two values are allowed for the bias: zero, or exactly -0.5 times the texture environment color. (This makes the expression C C +C equivalent to C C or (C -0.5)C , respectively.) t c b t c t c SEE ALSO glCopyPixels, glCopyTexImage1D, glCopyTexImage2D, glCopyTexSubImage1D, glCopyTexSubImage2D, glTexImage1D, glTexImage2D, glTexParameter, glTexSubImage1D, glTexSubImage2D