GLFOG(3G) GLFOG(3G)
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. GLFOGMODE,
GLFOGDENSITY, GLFOGSTART, GLFOGEND, and GLFOGINDEX 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. GLFOGMODE, GLFOGDENSITY,
GLFOGSTART, GLFOGEND, GLFOGINDEX, and GLFOGCOLOR are
accepted.
params Specifies the value or values to be assigned to pname.
GLFOGCOLOR 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
GLFOG.
glFog assigns the value or values in params to the fog parameter speci-
fied by pname. The following values are accepted for pname:
GLFOGMODE 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: GLINEAR, GLEXP, and GLEXP2. The
equations corresponding to these symbolic constants
are defined below. The initial fog mode is GLEXP.
GLFOGDENSITY 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.
GLFOGSTART 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.
GLFOGEND 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.
GLFOGINDEX params is a single integer or floating-point value
that specifies if, the fog color index. The ini-
tial fog index is 0.
GLFOGCOLOR params contains four integer or floating-point val-
ues 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 nega-
tive representable value maps to -1.0. Floating-
point values are mapped directly. After conver-
sion, 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 GLINEAR fog is
f = (end - z) / (end - start)
The equation for GLEXP fog is
f = e^-(density dot z)
The equation for GLEXP2 fog is
f = e^-( (density dot 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 Cr, are replaced by
Cr' = f * Cr ] (1-f) Cf
Fog does not affect a fragment's alpha component.
In color index mode, the fragment's color index ir is replaced by
ir'=ir](1-f)if
ERORS
GLINVALIDENUM is generated if pname is not an accepted value, or if
pname is GLFOGMODE and params is not an accepted value.
GLINVALIDVALUE is generated if pname is GLFOGDENSITY, and params is
negative.
GLINVALIDOPERATION is generated if glFog is executed between the exe-
cution of glBegin and the corresponding execution of glEnd.
ASOCIATED GETS
glIsEnabled with argument GLFOG
glGet with argument GLFOGCOLOR
glGet with argument GLFOGINDEX
glGet with argument GLFOGDENSITY
glGet with argument GLFOGSTART
glGet with argument GLFOGEND
glGet with argument GLFOGMODE
SEE ALSO
glEnable
GLFOG(3G)
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