glFog, glFogf, glFogi, glFogfv, glFogiv - specify fog
parameters
void glFogf(
GLenum pname,
const GLfloat param ); void glFogi(
GLenum pname,
const GLint param );
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.
void glFogfv(
GLenum pname,
const GLfloat *params ); void glFogiv(
GLenum pname,
const GLint *params );
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.
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
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 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. 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 floatingpoint
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 initial fog index
is 0. params contains four integer or floating-point values
that specify C[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
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]
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().
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
glEnable(3)
glFog(3G)
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