glFogi man page on Solaris

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GLFOG(3gl)							    GLFOG(3gl)

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,  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 param‐
	      eters accept an array containing only a single value.

DESCRIPTION
       Fog is initially disabled.  While enabled, fog affects rasterized geom‐
       etry, 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 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
			   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  if, the fog color index.  The ini‐
			   tial fog index is 0.

       GL_FOG_COLOR	   params contains four integer or floating-point val‐
			   ues that specify Cf, the fog color.	Integer values
			   are mapped linearly such  that  the	most  positive
			   representable value maps to 1.0, and the most nega‐
			   tive representable value maps to  -1.0.   Floating-
			   point  values  are  mapped directly.	 After conver‐
			   sion, all color components are clamped to the range
			   [0,1].  The initial fog color is (0, 0, 0, 0).

       GL_FOG_COORD_SRC	   params is a single integer value that is one of the
			   symbolic	constants     GL_FRAGMENT_DEPTH	    or
			   GL_FOG_COORD.  If the symbolic constant is GL_FRAG‐
			   MENT_DEPTH, then the fog fragment color is computed
			   based  on the eye-coordinate distance from the eye.
			   If the symbolic constant is GL_FOG_COORD, then  the
			   fog	fragment color is computed from the vertex fog
			   coordinate value specified by glFogCoord.  The ini‐
			   tial fog coordinate source is GL_FRAGMENT_DEPTH.

       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=_________

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 com‐
puted.	Then, if the GL is in RGBA color mode,	the  fragment's	 color	Cr  is
replaced by

			       Cr′=fCr+(1−f)Cf

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
       glGet with argument GL_FOG_COORD_SRC

SEE ALSO
       glEnable glFogCoord

				   15 Mar 97			    GLFOG(3gl)
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