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<STRONG>NAME</STRONG>
<STRONG>glFogf,</STRONG> <STRONG>glFogi,</STRONG> <STRONG>glFogfv,</STRONG> <STRONG>glFogiv</STRONG> - specify fog parameters
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glFogf</STRONG>( GLenum <EM>pname</EM>,
GLfloat <EM>param</EM> )
void <STRONG>glFogi</STRONG>( GLenum <EM>pname</EM>,
GLint <EM>param</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>pname</EM> Specifies a single-valued fog parameter.
<STRONG>GL_FOG_MODE</STRONG>, <STRONG>GL_FOG_DENSITY</STRONG>, <STRONG>GL_FOG_START</STRONG>,
<STRONG>GL_FOG_END</STRONG>, and <STRONG>GL_FOG_INDEX</STRONG> are accepted.
<EM>param</EM> Specifies the value that <EM>pname</EM> will be set to.
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glFogfv</STRONG>( GLenum <EM>pname</EM>,
const GLfloat *<EM>params</EM> )
void <STRONG>glFogiv</STRONG>( GLenum <EM>pname</EM>,
const GLint *<EM>params</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>pname</EM>
Specifies a fog parameter. <STRONG>GL_FOG_MODE</STRONG>,
<STRONG>GL_FOG_DENSITY</STRONG>, <STRONG>GL_FOG_START</STRONG>, <STRONG>GL_FOG_END</STRONG>, <STRONG>GL_FOG_INDEX</STRONG>,
and <STRONG>GL_FOG_COLOR</STRONG> are accepted.
<EM>params</EM>
Specifies the value or values to be assigned to <EM>pname</EM>.
<STRONG>GL_FOG_COLOR</STRONG> requires an array of four values. All
other parameters accept an array containing only a
single value.
<STRONG>DESCRIPTION</STRONG>
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
<STRONG>glEnable</STRONG> and <STRONG>glDisable</STRONG> with argument <STRONG>GL_FOG</STRONG>.
<STRONG>glFog</STRONG> assigns the value or values in <EM>params</EM> to the fog
parameter specified by <EM>pname</EM>. The following values are
accepted for <EM>pname</EM>:
<STRONG>GL_FOG_MODE</STRONG> <EM>params</EM> 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: <STRONG>GL_LINEAR</STRONG>, <STRONG>GL_EXP</STRONG>, and
<STRONG>GL_EXP2</STRONG>. The equations corresponding to
these symbolic constants are defined
below. The initial fog mode is <STRONG>GL_EXP</STRONG>.
<STRONG>GL_FOG_DENSITY</STRONG> <EM>params</EM> 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.
<STRONG>GL_FOG_START</STRONG> <EM>params</EM> 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.
<STRONG>GL_FOG_END</STRONG> <EM>params</EM> 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.
<STRONG>GL_FOG_INDEX</STRONG> <EM>params</EM> is a single integer or floating-
point value that specifies i , the fog
color index. The initial fo<STRONG>g</STRONG> index is
0.
<STRONG>GL_FOG_COLOR</STRONG> <EM>params</EM> contains four integer or
floating-point values that specify C ,
the fog color. Integer values are f
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 <STRONG>GL_LINEAR</STRONG> fog
is
f = __<STRONG>___</STRONG>_<STRONG>_</STRONG>_<STRONG>_</STRONG>__
end - start
The equation for <STRONG>GL_EXP</STRONG> fog is
f = e**(-(density . z))
The equation for <STRONG>GL_EXP2</STRONG> 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 color C is replaced by
r
C ' = fC +(1-f)C
r r f
In color index mode, the fragment's color index i is
replaced by r
i ' = i +(1-f)i
r r f
<STRONG>ERRORS</STRONG>
<STRONG>GL_INVALID_ENUM</STRONG> is generated if <EM>pname</EM> is not an accepted
value, or if <EM>pname</EM> is <STRONG>GL_FOG_MODE</STRONG> and <EM>params</EM> is not an
accepted value.
<STRONG>GL_INVALID_VALUE</STRONG> is generated if <EM>pname</EM> is <STRONG>GL_FOG_DENSITY</STRONG>,
and <EM>params</EM> is negative.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glFog</STRONG> is executed
between the execution of <STRONG>glBegin</STRONG> and the corresponding
execution of <STRONG>glEnd</STRONG>.
<STRONG>ASSOCIATED</STRONG> <STRONG>GETS</STRONG>
<STRONG>glIsEnabled</STRONG> with argument <STRONG>GL_FOG</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_COLOR</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_INDEX</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_DENSITY</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_START</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_END</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_FOG_MODE</STRONG>
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>glEnable</STRONG>
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