GLFOG(3G)																 GLFOG(3G)

NAME

       glFogf, glFogi, glFogfv, glFogiv - 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, and GL_FOG_INDEX 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, 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.

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 fac-
			   tor, 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 equa-
			   tion.  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 equa-
			   tion.  The initial far distance is 1.

       GL_FOG_INDEX	   params is a single integer or floating-point value that specifies if, the fog color index.  The initial fog index is 0.

       GL_FOG_COLOR	   params contains four integer or floating-point values that specify Cf, the fog color.  Integer values are  mapped  lin-
			   early  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).

       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  equa-
       tion for GL_LINEAR fog is

								       f=_________

       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, if the GL is in RGBA color mode, the fragment's
       red, green, and blue colors, represented by Cr, are replaced by

								     Cr'=fCr+(1-f)Cf

       Fog does not affect a fragment's alpha component.

       In color index mode, the fragment's color index ir is replaced by

								     ir'=ir+(1-f)if

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(3G)

																	 GLFOG(3G)