glFogFuncSGIS(3G)	       OpenGL Reference		     glFogFuncSGIS(3G)

NAME    [Toc]    [Back]

     glFogFuncSGIS - custom fog	blending function

C SPECIFICATION    [Toc]    [Back]

     void glFogFuncSGIS( GLsizei n,
			 const GLfloat *points )

PARAMETERS    [Toc]    [Back]

     n	     Specifies the number of control points in the custom fog blending
	     function.	The initial value is 1.

     points  Specifies an array	of control points.  Each control point
	     consists of two floating-point values.  The first is an eye-space
	     distance, and the second is a fog blending	factor in the range
	     [0.0,1.0].	 Blending factor 0.0 indicates full fog, and 1.0
	     indicates no fog.	The initial value is (0.0,1.0) (no fog).

DESCRIPTION    [Toc]    [Back]

     glFogFuncSGIS defines the control points for the custom fog blending
     function that is applied when the fog mode	is GL_FOG_FUNC_SGIS.  See
     glFog for a discussion of the various fog modes and the operation of the
     custom blending function.

     n is the number of	control	points in the custom fog blending function.
     It	must not be larger than	the value returned by glGet with argument
     GL_MAX_FOG_FUNC_POINTS_SGIS.  It must be at least 1.

     points is an array	of pairs of floating-point values that define the
     control points.  Each control point consists of an	eye-space distance
     from the viewpoint	(always	non-negative) and the corresponding fog
     blending factor (in the range [0.0,1.0]).	Blending factor	0.0 results in
     full fog, and 1.0 results in no fog.  The control points must be
     specified in order: eye space distance must not decrease from one control
     point to the next,	and the	fog blending factor must not increase from one
     control point to the next.

     n and points completely specify the custom	fog blending function,
     replacing any previous specification that may have	existed.

NOTES    [Toc]    [Back]

     Note that since each control point	is a pair of values, there are 2*n
     floating-point values in points.

     glFogFuncSGIS is part of the SGIS_fog_func	extension, not part of the
     core GL command set.  If GL_SGIS_fog_func is included in the string
     returned by glGetString when called with argument GL_EXTENSIONS,
     extension SGIS_fog_func is	supported by the connection.  See glIntro for
     more information about using extensions.





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glFogFuncSGIS(3G)	       OpenGL Reference		     glFogFuncSGIS(3G)

ERRORS    [Toc]    [Back]

     GL_INVALID_VALUE is generated if n	is less	than 1.

     GL_INVALID_VALUE is generated if any eye-space distance in	points is
     negative, or if any blend factor in points	is outside the range
     [0.0,1.0].

     GL_INVALID_VALUE is generated if the eye-space distance decreases from
     one control point to the next, or if the blending factor increases	from
     one control point to the next.

     GL_INVALID_OPERATION is generated if glFogFuncSGIS	is executed between
     the execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS    [Toc]    [Back]

     glGet with	argument GL_FOG_FUNC_SGIS
     glGet with	argument GL_FOG_FUNC_POINTS_SGIS
     glGet with	argument GL_MAX_FOG_FUNC_POINTS_SGIS


MACHINE	DEPENDENCIES
     Fog mode GL_FOG_FUNC_SGIS is supported only on InfiniteReality systems.

SEE ALSO    [Toc]    [Back]

     glFog


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