clipplane(3G)							 clipplane(3G)

NAME    [Toc]    [Back]

     clipplane - specify a plane against which all geometry is clipped

C SPECIFICATION    [Toc]    [Back]

     void clipplane(index, mode, params)
     long index, mode;
     float params[];

PARAMETERS    [Toc]    [Back]

     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:

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

	      CP_ON:  enable the (previously defined) clipplane.

	      CP_OFF:  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 CP_ON, or	CP_OFF.

DESCRIPTION    [Toc]    [Back]

     Geometry is always	clipped	against	the boundaries of a 6-plane frustum in
     x,	y, and z. clipplane 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.

     clipplane specifies a half-space using a 4-component plane	equation.
     When it is	called with mode CP_DEFINE, 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 clipplane with the CP_ON
     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 clipplane clipping is done in eyecoordinates,
 changes to the projection matrix have	no effect on its
     operation.



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clipplane(3G)							 clipplane(3G)



     By	default	all six	clipping planes	are undefined and disabled.  The
     behavior of an enabled but	undefined clipplane is undefined.

NOTES    [Toc]    [Back]

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

     clipplane cannot be used while mmode is MSINGLE.

     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    [Toc]    [Back]

     On	Impact and Infinite Reality clipplane cannot be	used with depthcue


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