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)
If pname is GL_TEXTURE_ENV_MODE, then params is (or points to) the symbolic name of a texture function. Three texture functions may be defined: GL_MODULATE, GL_DECAL, and GL_BLEND.
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 and glTexImage2D). 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.
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_INVALID_OPERATION is generated if glTexEnv is called between a call to glBegin and the corresponding call to glEnd.
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© 1995 Uwe Behrens. All rights reserved.