clippl(3G)

NAME
     clippl - specify a plane against which all geometry is clipped

FORTRAN SPECIFICATION
     subroutine clippl(index, mode, params)
     integer*4 index, mode
     real params()

PARAMETERS
     index    expects an integer in the range 0 through 5, indicating which of
              the 6 clipping planes is being modified.

     mode     expects one of three tokens:

              CPDEFI:  use the plane equation passed in params to define a
              clipplane.  The clipplane is neither enabled nor disabled.

              CPON:  enable the (previously defined) clipplane.

              CPOFF:  disable the clipplane. (default)

     params   expects an array of 4 floats that specify a plane equation.  A
              plane equation is usually thought of as a 4-vector [A,B,C,D].
              In this case, A is the first component of the params array, and
              D is the last.  A 4-component vertex array (see v4f) can be
              passed as a plane equation, where vertex X becomes A, Y becomes
              B, etc.  The specified contents of params are insignificant when
              mode is

DESCRIPTION
     Geometry is always clipped against the boundaries of a 6-plane frustum in
     x, y, and z. clippl allows the specification of additional planes, not
     necessarily perpendicular to the x, y, or z axes, against which all
     geometry is clipped.  Up to 6 additional planes can be specified.
     Because the resulting clipping region is always the intersection of the
     (up to) 12 half-spaces, it is always convex.

     clippl specifies a half-space using a 4-component plane equation.  When
     it is called with mode CPDEFI, this object-coordinate plane equation is
     transformed to eye-coordinates using the inverse of the current ModelView
     matrix.

     A defined clipplane is then enabled by calling clippl with the CPON
     argument, and with arbitrary values passed in params.  While drawing
     after a clipplane has been defined and enabled, each vertex is
     transformed to eye-coordinates, where it is dotted with the transformed
     clipping plane equation.  Eye-coordinate vertexes whose dot product with
     the transformed clipping plane equation is positive or zero are in, and
     require no clipping.  Those eye-coordinate vertexes whose dot product is
     negative are clipped.  Because clippl clipping is done in eye-
     coordinates, changes to the projection matrix have no effect on its
     operation.
     By default all six clipping planes are undefined and disabled.  The
     behavior of an enabled but undefined clipplane is undefined.

NOTES
     IRIS-4D models G, GT, and GTX, and the Personal Iris, do not implement
     clippl.  Use getgde to determine whether user-defined clipping planes are
     supported.

     clippl cannot be used while mmode is MSINGL.

     A point and a normal are converted to a plane equation in the following
     manner:

          point = [Px,Py,Pz]

          normal = |Nx|
                   |Ny|
                   |Nz|

          plane equation = |A|
                           |B|
                           |C|
                           |D|
              A = Nx
              B = Ny
              C = Nz
              D = -[Px,Py,Pz] dot |Nx|
                         |Ny|
                         |Nz|


BUGS
     On Impact and Infinite Reality clippl cannot be used with depthc