fglFogFuncSGIS(3G)

NAME
     fglFogFuncSGIS - custom fog blending function


FORTRAN SPECIFICATION
     SUBROUTINE fglFogFuncSGIS( INTEGER*4 n,
                                CHARACTER*8 points )


PARAMETERS
     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
     fglFogFuncSGIS defines the control points for the custom fog blending
     function that is applied when the fog mode is GL_FOG_FUNC_SGIS.  See
     fglFog 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 fglGet 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
     Note that since each control point is a pair of values, there are 2*n
     floating-point values in points.

     fglFogFuncSGIS 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 fglGetString when called with argument GL_EXTENSIONS,
     extension SGIS_fog_func is supported by the connection.  See fglIntro for
     more information about using extensions.
ERRORS
     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 fglFogFuncSGIS is executed between
     the execution of fglBegin and the corresponding execution of fglEnd.

ASSOCIATED GETS
     fglGet with argument GL_FOG_FUNC_SGIS
     fglGet with argument GL_FOG_FUNC_POINTS_SGIS
     fglGet with argument GL_MAX_FOG_FUNC_POINTS_SGIS


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


SEE ALSO
     fglFog