glFogf man page on DigitalUNIX

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glFog(3G)							     glFog(3G)

NAME
       glFog, glFogf, glFogi, glFogfv, glFogiv - specify fog parameters

SYNOPSIS
       void glFogf(
	       GLenum pname,
	       const GLfloat param ); void glFogi(
	       GLenum pname,
	       const GLint param );

PARAMETERS
       Specifies  a single-valued fog parameter.  GL_FOG_MODE, GL_FOG_DENSITY,
       GL_FOG_START, GL_FOG_END, GL_FOG_INDEX, and GL_FOG_COLOR are  accepted.
       Specifies the value that pname will be set to.

SYNOPSIS
       void glFogfv(
	       GLenum pname,
	       const GLfloat *params ); void glFogiv(
	       GLenum pname,
	       const GLint *params );

PARAMETERS
       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.	 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 geome‐
       try, 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: 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 con‐
       stants are accepted: GL_LINEAR, GL_EXP, and GL_EXP2. The equations cor‐
       responding  to  these symbolic constants are defined below. The initial
       fog mode is GL_EXP.  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.  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.  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.	 params is a single integer or
       floating-point value that specifies i[f], the fog color index. The ini‐
       tial  fog  index	 is 0.	params contains four integer or floating-point
       values that specify C[f], 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 val‐
       ues  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  posttex‐
       turing  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) over (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, 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]'  =
       fC[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]

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(3)

								     glFog(3G)
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