glFog(3G)glFog(3G)NAME
glFog, glFogf, glFogi, glFogfv, glFogiv - specify fog parameters
SYNOPSIS
void glFogf(
GLenum pname,
const GLfloat param ); void glFogi(
GLenum pname,
const GLint param );
PARAMETERS
Specifies a single-valued fog parameter. GL_FOG_MODE, GL_FOG_DENSITY,
GL_FOG_START, GL_FOG_END, GL_FOG_INDEX, and GL_FOG_COLOR are accepted.
Specifies the value that pname will be set to.
SYNOPSIS
void glFogfv(
GLenum pname,
const GLfloat *params ); void glFogiv(
GLenum pname,
const GLint *params );
PARAMETERS
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. 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 initially disabled. While enabled, fog affects rasterized geome‐
try, 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: 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 cor‐
responding to these symbolic constants are defined below. The initial
fog mode is GL_EXP. 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. 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. 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. params is a single integer or
floating-point value that specifies i[f], the fog color index. The ini‐
tial fog index is 0. params contains four integer or floating-point
values that specify C[f], the fog color. Integer values are mapped lin‐
early such that the most positive representable value maps to 1.0, and
the most negative representable value maps to -1.0. Floating-point val‐
ues 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 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.z)
The equation for GL_EXP2 fog is f = e^-(density.z)^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[r], are replaced by (C[r]' =
fC[r] + (1-f) C[f]
Fog does not affect a fragment's alpha component.
In color index mode, the fragment's color index i[r] is replaced by
(i[r]' = i[r] + (1-f) i[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
execution of glBegin() and the corresponding execution of glEnd().
ASSOCIATED GETSglIsEnabled() 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 ALSOglEnable(3)glFog(3G)