glFogf
, glFogx
, glFogfv
, glFogxv
- specify fog parameters
void glFogf(GLenum pname, GLfloat param) void glFogx(GLenum pname, GLfixed param)
pname
Specifies a single-valued fog parameter. GL_FOG_MODE
, GL_FOG_DENSITY
, GL_FOG_START
, and GL_FOG_END
are accepted.
param
Specifies the value that pname
will be set to.
void glFogfv(GLenum pname, const GLfloat * params) void glFogxv(GLenum pname, const GLfixed * params)
pname
Specifies a fog parameter. GL_FOG_MODE
, GL_FOG_DENSITY
, GL_FOG_START
, GL_FOG_END
, 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.
If fog is 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
. Fog is initially disabled.
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 fixed-point 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 fixed-point 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 fixed-point 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 fixed-point or floating-point value that specifies end, the far distance used in the linear fog equation. The initial far distance is 1.
GL_FOG_COLOR
params
contains four fixed-point or floating-point values that specify Cf, the fog color. Both fixed-point and 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)/(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, the fragment's red, green, and blue colors, represented by Cr, are replaced by
C'r = f Cr + (1 - f) Cf
Fog does not affect a fragment's alpha component.
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.
Copyright © 2003-2004 Silicon Graphics, Inc.
This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.