glFogFuncSGIS(3G) OpenGL Reference glFogFuncSGIS(3G)
NAME
glFogFuncSGIS - custom fog blending function
C SPECIFICATION
void glFogFuncSGIS( GLsizei n,
const GLfloat *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
glFogFuncSGIS defines the control points for the custom fog blending
function that is applied when the fog mode is GLFOGFUNCSGIS. 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
GLMAXFOGFUNCPOINTSSGIS. 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.
glFogFuncSGIS is part of the SGISfogfunc extension, not part of the
core GL command set. If GLSGISfogfunc is included in the string
returned by glGetString when called with argument GLEXTENSIONS,
extension SGISfogfunc is supported by the connection. See glIntro for
more information about using extensions.
Page 1
glFogFuncSGIS(3G) OpenGL Reference glFogFuncSGIS(3G)
ERRORS
GLINVALIDVALUE is generated if n is less than 1.
GLINVALIDVALUE 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].
GLINVALIDVALUE 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.
GLINVALIDOPERATION is generated if glFogFuncSGIS is executed between
the execution of glBegin and the corresponding execution of glEnd.
ASSOCIATED GETS
glGet with argument GLFOGFUNCSGIS
glGet with argument GLFOGFUNCPOINTSSGIS
glGet with argument GLMAXFOGFUNCPOINTSSGIS
MACHINE DEPENDENCIES
Fog mode GLFOGFUNCSGIS is supported only on InfiniteReality systems.
SEE ALSO
glFog
Page 2