glFog — specify fog parameters
void glFogf( | GLenum | pname, |
GLfloat | param) ; |
void glFogi( | GLenum | pname, |
GLint | param) ; |
pname
Specifies a single-valued fog parameter.
GL_FOG_MODE
,
GL_FOG_DENSITY
,
GL_FOG_START
,
GL_FOG_END
,
GL_FOG_INDEX
, and
GL_FOG_COORD_SRC
are accepted.
param
Specifies the value that pname
will be set to.
void glFogfv( | GLenum | pname, |
const GLfloat * | params) ; |
void glFogiv( | GLenum | pname, |
const GLint * | params) ; |
pname
Specifies a fog parameter.
GL_FOG_MODE
,
GL_FOG_DENSITY
,
GL_FOG_START
,
GL_FOG_END
,
GL_FOG_INDEX
,
GL_FOG_COLOR
, and
GL_FOG_COORD_SRC
are accepted.
params
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.
Fog is initially disabled.
While enabled, fog affects rasterized geometry,
bitmaps, and pixel blocks, but not buffer clear operations. To enable
and disable fog, call glEnable and glDisable with argument
GL_FOG
.
glFog
assigns the value or values in params
to the fog parameter
specified by pname
.
The following values are accepted for pname
:
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,
GL_LINEAR
,
GL_EXP
,
and GL_EXP2
.
The equations corresponding to these symbolic constants are defined below.
The initial fog mode is GL_EXP
.
GL_FOG_DENSITY
params
is a single integer or floating-point value that specifies
GL_FOG_START
params
is a single integer or floating-point value that specifies
GL_FOG_END
params
is a single integer or floating-point value that specifies
GL_FOG_INDEX
params
is a single integer or floating-point value that specifies
GL_FOG_COLOR
params
contains four integer or floating-point values that specify
GL_FOG_COORD_SRC
params
contains either of the following symbolic constants:
GL_FOG_COORD
or GL_FRAGMENT_DEPTH
. GL_FOG_COORD
specifies that the current fog coordinate should be used as distance value
in the fog color computation. GL_FRAGMENT_DEPTH
specifies that the
current fragment depth should be used as distance value in the fog
computation.
Fog blends a fog color with each rasterized pixel fragment's post-texturing
color using a blending factor
GL_FOG_COORD_SRC
is GL_FRAGMENT_DEPTH
) or
the current fog coordinate (in the case that GL_FOG_COORD_SRC
is GL_FOG_COORD
).
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,
Fog does not affect a fragment's alpha component.
In color index mode, the fragment's color index
GL_INVALID_ENUM
is generated if pname
is not an accepted value,
or if pname
is GL_FOG_MODE
and params
is not an accepted value.
GL_INVALID_VALUE
is generated if pname
is GL_FOG_DENSITY
and params
is negative.
GL_INVALID_OPERATION
is generated if glFog
is executed between the execution of glBegin
and the corresponding execution of glEnd.
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_FOG_MODE
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.