GLfloat param )
       void GLAPIENTRY 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 GLAPIENTRY glFogfv( GLenum pname,
                                const GLfloat *params )
       void GLAPIENTRY 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  ac‐
              cepted.

       params Specifies   the   value  or  values  to  be  assigned  to  pname.
              GL_FOG_COLOR requires an array of four values.  All other parame‐
              ters accept an array containing only a single value.

DESCRIPTION
       Fog is initially disabled.  While enabled, fog affects rasterized geome‐
       try, bitmaps, and pixel blocks, but not buffer clear operations. To  en‐
       able and disable fog, call glEnable and glDisable with argument GL_FOG.

       glFog  assigns the value or values in params to the fog parameter speci‐
       fied 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 densi‐
                           ties 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
                           The initial fog color is (0, 0, 0, 0).

       Fog blends a fog color with each rasterized pixel fragment's posttextur‐
       ing  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 co‐
       ordinates  from  the  origin to the fragment being fogged.  The equation
       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  exe‐
       cution 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