glClipPlane -	specify	a plane	against	which all geometry is
clipped

glClipPlane
	glClipPlane(plane, equation[]) -> None

void glClipPlane( GLenum plane,
                  const GLdouble *equation )

plane	    Specifies which clipping plane is being
          positioned.	 Symbolic names	of the form
          GL_CLIP_PLANEi, where i is an integer between 0
          and	GL_MAX_CLIP_PLANES -1, are accepted.

equation  Specifies the address of an	array of four double-
          precision floating-point values.  These values are
          interpreted	as a plane equation.

Geometry is always clipped against the boundaries of a six-
plane	frustum	in x, y, and z.	glClipPlane allows the
specification	of additional planes, not necessarily
perpendicular	to the x, y, or	z axis,	against	which all
geometry is clipped.	To determine the maximum number	of
additional clipping planes, call glGetIntegerv with argument
GL_MAX_CLIP_PLANES. All implementations support at least six
such clipping	planes.	Because	the resulting clipping region
is the intersection of the defined half-spaces, it is	always
convex.

glClipPlane specifies	a half-space using a four-component
plane	equation.  When	glClipPlane is called, equation	is
transformed by the inverse of	the modelview matrix and
stored in the	resulting eye coordinates.  Subsequent changes
to the modelview matrix have no effect on the	stored plane-
equation components.	If the dot product of the eye
coordinates of a vertex with the stored plane	equation
components is	positive or zero, the vertex is	in with
respect to that clipping plane.  Otherwise, it is out.

To enable and	disable	clipping planes, call glEnable and
glDisable with the argument GL_CLIP_PLANEi, where i is the
plane	number.

All clipping planes are initially defined as (0, 0, 0, 0) in
eye coordinates and are disabled.

It is	always the case	that GL_CLIP_PLANEi = GL_CLIP_PLANE0 +
i.

GL_INVALID_ENUM is generated if plane	is not an accepted
value.

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

glGetClipPlane
glIsEnabled with argument GL_CLIP_PLANEi

glEnable