NAME
glFogf, glFogi, glFogfv, glFogiv
- specify fog parameters
C SPECIFICATION
void ggllFFooggff(
GLenum _p_n_a_m_e,
GLfloat _p_a_r_a_m )
void ggllFFooggii(
GLenum _p_n_a_m_e,
GLint _p_a_r_a_m )
delim $$
PARAMETERS
-
_p_n_a_m_e
-
Specifies a single-valued fog parameter.
GGLL__FFOOGG__MMOODDEE,
GGLL__FFOOGG__DDEENNSSIITTYY,
GGLL__FFOOGG__SSTTAARRTT,
GGLL__FFOOGG__EENNDD,
and
GGLL__FFOOGG__IINNDDEEXX
are accepted.
-
_p_a_r_a_m
-
Specifies the value that _p_n_a_m_e will be set to.
C SPECIFICATION
void ggllFFooggffvv(
GLenum _p_n_a_m_e,
const GLfloat _*_p_a_r_a_m_s )
void ggllFFooggiivv(
GLenum _p_n_a_m_e,
const GLint _*_p_a_r_a_m_s )
PARAMETERS
-
_p_n_a_m_e
-
Specifies a fog parameter.
GGLL__FFOOGG__MMOODDEE,
GGLL__FFOOGG__DDEENNSSIITTYY,
GGLL__FFOOGG__SSTTAARRTT,
GGLL__FFOOGG__EENNDD,
GGLL__FFOOGG__IINNDDEEXX,
and
GGLL__FFOOGG__CCOOLLOORR
are accepted.
-
_p_a_r_a_m_s
-
Specifies the value or values to be assigned to _p_n_a_m_e.
GGLL__FFOOGG__CCOOLLOORR requires an array of four values.
All other parameters accept an array containing only a single value.
DESCRIPTION
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 ggllEEnnaabbllee and ggllDDiissaabbllee with argument
GGLL__FFOOGG.
ggllFFoogg assigns the value or values in _p_a_r_a_m_s to the fog parameter
specified by _p_n_a_m_e.
The following values are accepted for _p_n_a_m_e:
-
GGLL__FFOOGG__MMOODDEE
-
_p_a_r_a_m_s 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:
GGLL__LLIINNEEAARR,
GGLL__EEXXPP,
and GGLL__EEXXPP22.
The equations corresponding to these symbolic constants are defined below.
The initial fog mode is GGLL__EEXXPP.
-
GGLL__FFOOGG__DDEENNSSIITTYY
-
_p_a_r_a_m_s 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.
-
GGLL__FFOOGG__SSTTAARRTT
-
_p_a_r_a_m_s 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.
-
GGLL__FFOOGG__EENNDD
-
_p_a_r_a_m_s 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.
-
GGLL__FFOOGG__IINNDDEEXX
-
_p_a_r_a_m_s is a single integer or floating-point value that specifies
$i sub f$,
the fog color index.
The initial fog index is 0.
-
GGLL__FFOOGG__CCOOLLOORR
-
_p_a_r_a_m_s contains four integer or floating-point values that specify
$C sub f$, 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 initial 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 GGLL__LLIINNEEAARR fog is
f ~=~ {end ~-~ z} over {end ~-~ start}
The equation for GGLL__EEXXPP fog is
f ~=~ e sup {-^(density ~cdot~ z)}
The equation for GGLL__EEXXPP22 fog is
f ~=~ e sup {-^(density ~cdot~ z)} sup 2
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 red, green, and blue colors, represented by $C sub r$,
are replaced by
{C sub r} sup prime ~=~ f^C sub r ~+~ (1 - f)^C sub f
Fog does not affect a fragment's alpha component.
In color index mode, the fragment's color index $i sub r$ is replaced by
{i sub r} sup prime ~=~ i sub r ~+~ (1 - f)^i sub f
ERRORS
GGLL__IINNVVAALLIIDD__EENNUUMM is generated if _p_n_a_m_e is not an accepted value,
or if _p_n_a_m_e is GGLL__FFOOGG__MMOODDEE and _p_a_r_a_m_s is not an accepted value.
GGLL__IINNVVAALLIIDD__VVAALLUUEE is generated if _p_n_a_m_e is GGLL__FFOOGG__DDEENNSSIITTYY,
and _p_a_r_a_m_s is negative.
GGLL__IINNVVAALLIIDD__OOPPEERRAATTIIOONN is generated if ggllFFoogg
is executed between the execution of ggllBBeeggiinn
and the corresponding execution of ggllEEnndd.
ASSOCIATED GETS
ggllIIssEEnnaabblleedd with argument GGLL__FFOOGG
ggllGGeett with argument GGLL__FFOOGG__CCOOLLOORR
ggllGGeett with argument GGLL__FFOOGG__IINNDDEEXX
ggllGGeett with argument GGLL__FFOOGG__DDEENNSSIITTYY
ggllGGeett with argument GGLL__FFOOGG__SSTTAARRTT
ggllGGeett with argument GGLL__FFOOGG__EENNDD
ggllGGeett with argument GGLL__FFOOGG__MMOODDEE
SEE ALSO
ggllEEnnaabbllee((33GG))