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			  03/16/2013			     GLFOG(3G)

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