glFog man page on Oracle
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GLFOG(3G) OpenGL Manual GLFOG(3G)
NAME
glFog - 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 parameters
accept an array containing only a single value.
DESCRIPTION
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:
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 i
f, the fog color index. The initial fog index is 0.
GL_FOG_COLOR
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).
GL_FOG_COORD_SRC
params contains either of the following symbolic constants:
GL_FOG_COORD or GL_FRAGMENT_DEPTH. GL_FOG_COORD specifies that the
current fog coordinate should be used as distance value in the fog
color computation. GL_FRAGMENT_DEPTH specifies that the current
fragment depth should be used as distance value in the fog
computation.
Fog blends a fog color with each rasterized pixel fragment's
post-texturing color using a blending factor f. Factor f is computed in
one of three ways, depending on the fog mode. Let c be either the
distance in eye coordinate from the origin (in the case that the
GL_FOG_COORD_SRC is GL_FRAGMENT_DEPTH) or the current fog coordinate
(in the case that GL_FOG_COORD_SRC is GL_FOG_COORD). The equation for
GL_LINEAR fog is f = end - c end - start
The equation for GL_EXP fog is f = e - density ⋅ c
The equation for GL_EXP2 fog is f = e - density ⋅ c 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 ″ = f × C 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
NOTES
GL_FOG_COORD_SRC is available only if the GL version is 1.4 or greater.
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
execution 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
SEE ALSO
glEnable()
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
under the SGI Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.
AUTHORS
opengl.org
opengl.org 04/29/2014 GLFOG(3G)
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