GLFOG()GLFOG()NAME
glFogf, glFogi, glFogfv, glFogiv - specify fog parameters
C SPECIFICATION
void glFogf( GLenum pname,
GLfloat param )
void glFogi( GLenum pname,
GLint param )
delim $$
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.
params Specifies the value or values to be assigned to pname.
GL_FOG_COLOR requires an array of four values. All other param‐
eters accept an array containing only a single value.
DESCRIPTION
Fog is initially disabled. While enabled, fog affects rasterized geom‐
etry, 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 speci‐
fied 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, $f$. Three symbolic con‐
stants are accepted: GL_LINEAR, GL_EXP, and
GL_EXP2. The equations corresponding to these sym‐
bolic 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 $density$, the fog density used in
both exponential fog equations. Only nonnegative
densities are accepted. The initial fog density is
1.
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 initial near distance
is 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 initial far distance is
1.
GL_FOG_INDEX params is a single integer or floating-point value
that specifies $i sub f$, the fog color index. The
initial fog index is 0.
GL_FOG_COLOR params contains four integer or floating-point val‐
ues that specify $C sub f$, the fog color. Integer
values are mapped linearly such that the most posi‐
tive representable value maps to 1.0, and the most
negative representable value maps to -1.0. Float‐
ing-point values are mapped directly. After con‐
version, all color components are clamped to the
range [0,1]. The initial fog color is (0, 0, 0,
0).
Fog blends a fog color with each rasterized pixel fragment's posttex‐
turing 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
f ~=~ {end ~-~ z} over {end ~-~ start}
The equation for GL_EXP fog is
f ~=~ e ** (-(density ~cdot~ z))
The equation for GL_EXP2 fog is
f ~=~ e ** (-(density ~cdot~ z) ** 2)
Regardless of the fog mode, $f$ is clamped to the range [0,1] after it is com‐
puted. Then, if the GL is in RGBA color mode, the fragment's color $C sub r$
is replaced by
{C sub r} prime ~=~ f C sub r + (1 - f) C sub f
In color index mode, the fragment's color index $i sub r$ is replaced by
{i sub r} prime ~=~ i sub r + (1 - f) i sub f
ERRORS
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 exe‐
cution of glBegin and the corresponding execution of 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_FOG_MODE
SEE ALSO
glEnable
GLFOG()
