glGetClipPlane

glGetClipPlane - return the coefficients of the specified clipping plane

void glGetClipPlane(GLenum plane,
                    GLdouble *equation)

plane	Specifies a clipping plane. The number of clipping planes depends on the implementation, but at least six clipping planes are supported. They are identified by symbolic names of the form GL_CLIP_PLANEi where 0 < i < GL_MAX_CLIP_PLANES.
equation	Returns four double-precision values that are the coefficients of the plane equation of plane in eye coordinates. The initial value is (0, 0, 0, 0).

glGetClipPlane returns in equation the four coefficients of the plane equation for plane.

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

If an error is generated, no change is made to the contents of equation.

GL_INVALID_ENUM is generated if plane is not an accepted value.

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