glFog
NAME
glFogf, glFogi, glFogfv, glFogiv -- specify fog parameters
C SPECIFICATION
void glFogf(GLenum pname,
GLfloat param)
void glFogi(GLenum pname,
GLint param)
PARAMETERS
- pname
-
Specifies a single-valued fog parameter. GL_FOG_MODE,
GL_FOG_DENSITY, GL_FOG_START, GL_FOG_END, and
GL_FOG_INDEX are accepted.
- param
-
Specifies the value that pname will be set to.
C SPECIFICATION
void glFogfv(GLenum pname,
const GLfloat *params)
void glFogiv(GLenum pname,
const GLint *params)
PARAMETERS
- pname
-
Specifies a fog parameter. GL_FOG_MODE,
GL_FOG_DENSITY, GL_FOG_START, GL_FOG_END,
GL_FOG_INDEX, and GL_FOG_COLOR are accepted.
- param
-
Specifies the value or values to be assigned to pname.
GL_FOG_COLOR requires an array of four values. All other
parameters accept an array containing only a single value.
DESCRIPTION
Fog is enabled and disabled with
glEnable and
glDisableusing the argument
GL_FOG. While enabled, fog affects rasterized geometry, bitmaps, and
pixel blocks, but not buffer clear operations.
glFog assigns the value or values in params to the fog parameter
specified by pname. The accepted values for pname are as follows:
- GL_FOG_MODE
-
params is a single integer or floating-point value that specifies
the equation to be used to compute the fog blend factor, f.
Three symbolic constants are accepted: GL_LINEAR,
GL_EXP, and GL_EXP2. The equations corresponding to these
symbolic constants are defined below. The default fog mode is
GL_EXP.
- GL_FOG_DENSITY
-
params is a single integer or floating-point value that
specifies density, the fog density used in both exponential fog
equations. Only nonnegative densities are accepted. The default fog
density is 1.0.
- GL_FOG_START
-
params is a single integer or floating-point value that
specifies start, the near distance used in the linear fog
equation. The default near distance is 0.0.
- GL_FOG_END
-
params is a single integer or floating-point value that
specifies end, the far distance used in the linear fog equation.
The default far distance is 1.0.
- GL_FOG_INDEX
-
params is a single integer or floating-point value that
specifies if, the fog color index. The default fog index is
0.0.
- GL_FOG_COLOR
-
params contains four integer or floating-point values that
specify Cf, the fog color. Integer values are mapped linearly
such that the most positive representable value maps to 1.0, and the
most negative representable value maps to -1.0. Floating-point values
are mapped directly. After conversion, all color components are clamped
to the range [0, 1]. The default fog color is (0,0,0,0).
Fog blends a fog color with each rasterized pixel fragment's posttexturing
color using a blending factor f. Factor f is computed in one of
three ways, depending on the fog mode. Let z be the distance in eye
coordinates from the origin to the fragment being fogged. The equation for
GL_LINEAR fog is
The equation for GL_EXP fog is
The equation for GL_EXP2 fog is
Regardless of the fog mode, f is clamped to the range [0 ,1] after it is
computed. Then, if the GL is in RGBA color mode, the fragment's color Cr
is replaced by
Cr' = f*Cr+(1-f)*Cf
In color index mode, the fragment's color index ir is replaced by
ir' = f*ir+(1-f)*if
ERRORS
GL_INVALID_ENUM is generated if pname is not an accepted value.
GL_INVALID_OPERATION is generated if glFog is called
between a call to glBegin and the
corresponding call to glEnd.
ASSOCIATED GETS
glIsEnabled with argument
GL_FOG
glGet with argument
GL_FOG_COLOR
glGet with argument
GL_FOG_INDEX
glGet with argument
GL_FOG_DENSITY
glGet with argument
GL_FOG_START
glGet with argument
GL_FOG_END
glGet with argument
GL_MODE
SEE ALSO
glEnable
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© 1995 Uwe Behrens. All rights reserved.