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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 x C r + 1 - f x 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 x 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 (C) 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				    06/10/2014					GLFOG(3G)
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