OpenGL man pages
glFogf, glFogi, glFogfv, glFogiv - specify fog parameters
void glFogf( GLenum pname, GLfloat param ) void glFogi( GLenum pname, GLint param )
pname Specifies a single-valued fog parameter. GL_FOG_MODE, GL_FOG_DENSITY, GL_FOG_START, GL_FOG_END, and GL_FOG_INDEX are accepted. param Specifies the value that pname will be set to.
void glFogfv( GLenum pname, const GLfloat *params ) void glFogiv( GLenum pname, const GLint *params )
pname
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.
params
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 enabled and disabled with glEnable and glDisable using the argument
GL_FOG. While enabled, fog affects rasterized geometry, bitmaps, and pixel
blocks, but not buffer clear operations.
glFog assigns the value or values in params to the fog parameter specified
by pname. The accepted values for pname are as follows:
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 default 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 default fog density is 1.0.
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 default near distance is 0.0.
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 default far distance is 1.0.
GL_FOG_INDEX params is a single integer or floating-point value that
specifies i , the fog color index. The default fog
f
index is 0.0.
GL_FOG_COLOR params 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
default 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
end - z
f = -----------
end - start
The equation for GL_EXP fog is
-(density · z)
f = e
The equation for GL_EXP2 fog is
2
-(density · z)
f = e
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 Cr
is replaced by
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
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 called between a call to glBegin and the corresponding call to 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
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Last Edited:
Fri Dec 6 11:18:03 EST 1996
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