GLFOG(3gl)GLFOG(3gl)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. 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.
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, 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 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 constants
are accepted: 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 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 if, the fog color index. The ini‐
tial fog index is 0.
GL_FOG_COLOR 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).
GL_FOG_COORD_SRC params is a single integer value that is one of the
symbolic constants GL_FRAGMENT_DEPTH or
GL_FOG_COORD. If the symbolic constant is GL_FRAG‐
MENT_DEPTH, then the fog fragment color is computed
based on the eye-coordinate distance from the eye.
If the symbolic constant is GL_FOG_COORD, then the
fog fragment color is computed from the vertex fog
coordinate value specified by glFogCoord. The ini‐
tial fog coordinate source is GL_FRAGMENT_DEPTH.
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=_________
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 com‐
puted. Then, if the GL is in RGBA color mode, the fragment's color Cr is
replaced by
Cr′=fCr+(1−f)Cf
In color index mode, the fragment's color index ir is replaced by
ir′=ir+(1−f)if
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
glGet with argument GL_FOG_COORD_SRC
SEE ALSO
glEnable glFogCoord
15 Mar 97 GLFOG(3gl)