glTexEnvf,
glTexEnvi, glTexEnvfv, glTexEnviv
[New
- Windows 95, OEM Service Release 2]
These
functions set texture environment parameters.
void glTexEnvf(
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GLenum target, |
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GLenum pname, |
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GLfloat param |
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); |
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void glTexEnvi(
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GLenum target, |
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GLenum pname, |
|
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GLint param |
|
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); |
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Parameters
target
A texture
environment. Must be GL_TEXTURE_ENV.
pname
The symbolic
name of a single-valued texture environment parameter. Must be
GL_TEXTURE_ENV_MODE.
param
A single
symbolic constant, one of GL_MODULATE, GL_DECAL, or GL_BLEND.
void glTexEnvfv(
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GLenum target, |
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GLenum pname, |
|
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const GLfloat *params |
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); |
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void glTexEnviv(
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GLenum target, |
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GLenum pname, |
|
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const GLint *params |
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); |
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Parameters
target
A texture
environment. Must be GL_TEXTURE_ENV.
pname
The symbolic
name of a texture environment parameter. Accepted values are
GL_TEXTURE_ENV_MODE and GL_TEXTURE_ENV_COLOR.
params
A pointer to
an array of parameters: either a single symbolic constant or an RGBA color.
Remarks
A texture
environment specifies how texture values are interpreted when a fragment is
textured. The target parameter must be GL_TEXTURE_ENV. The pname
parameter can be either GL_TEXTURE_ENV_MODE or GL_TEXTURE_ENV_COLOR.
If pname
is GL_TEXTURE_ENV_MODE, then params is (or points to) the symbolic name
of a texture function. Three texture functions are 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, 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) .
{bml bm55.BMP}
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).
The following
function retrieves information related to glTexEnv:
glGetTexEnv
Error Codes
The following
are the error codes generated and their conditions.
|
Error
Code |
Condition |
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GL_INVALID_ENUM
|
target or pname was not one of the accepted defined
values, or when params should have had a defined constant value (based
on the value of pname) and did not. |
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GL_INVALID_OPERATION
|
glTexEnv was called between a call to glBegin and the
corresponding call to glEnd. |
See Also