polymode(3G)							  polymode(3G)

NAME    [Toc]    [Back]

     polymode -	control	the rendering of polygons

C SPECIFICATION    [Toc]    [Back]

     void polymode(long	mode)

PARAMETERS    [Toc]    [Back]

     mode   Expects one	of the symbolic	constants:

	    PYM_POINT, draw only points	at the vertices.

	    PYM_LINE, draw lines from vertex to	vertex.

	    PYM_FILL, fill the polygon interior.

	    PYM_HOLLOW,	fill only interior pixels at the boundaries.

DESCRIPTION    [Toc]    [Back]

     polymode specifies	whether	polygons are filled, outlined, drawn with
     points at their vertices, or outlined with	a hollow fill algorithm.
     Affected polygons include all polygons that are normally filled,
     including those generated by bgnpolygon and endpolygon, by	bgntmesh and
     endtmesh, by bgnqstrip and	endqstrip, by arcf, circf, and rectf, and by
     NURBS surfaces.  Also affected are	polygons generated by the obsolete
     pmv, pdr, and pclos commands, and by polf and spolf.

     PYM_FILL is the default mode.  In this mode polygons are filled with a
     point-sample algorithm.  (Refer to	the Graphics Library Programmer's
     Guide for an detailed explanation of point-sampling.)

     PYM_POINT causes a	single point to	be drawn at each polygon vertex,
     including vertices	generated by clipping.	All point rendering modes,
     including antialiasing specified by pntsmooth, apply to these points.

     PYM_LINE causes lines to be drawn from vertex to vertex around the
     perimeter of the polygon.	This line forms	a single outline, because it
     passes through both projected vertices and	vertices generated by
     clipping.	All line rendering modes, including line width,	line stipple
     style, and	line antialiasing specified by linesmooth, apply to these
     lines.

     PYM_HOLLOW	supports a special kind	of polygon fill	with the following
     properties:

     1.	  Only pixels on the polygon edge are filled.  These pixels form a
	  single-width line (regardless	of the current linewidth) around the
	  inner	perimeter of the polygon.

     2.	  Only pixels that would have been filled (PYM_FILL) are changed (i.e.
	  the outline does not extend beyond the exact polygon boundary).





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polymode(3G)							  polymode(3G)



     3.	  Pixels that are changed take the exact color and depth values	that
	  they would have had the polygon been filled.

     Because their pixel depth values are exact, hollow	polygons can be
     composed with filled polygons accurately.	Both hidden-line and scribedsurface
 renderings	can be done taking advantage of	this fact.

SEE ALSO    [Toc]    [Back]

     bgnpolygon, endpolygon, polysmooth, stencil

NOTES    [Toc]    [Back]

     XS, XZ, Elan, and Extreme graphics	support	all polymode options except
     polymode(PYM_HOLLOW).  IRIS-4D G, GT, and GTX models, as well as the
     Personal Iris, Iris Entry,	Indy, and XL systems do	not support polymode.
     Use getgdesc to determine whether support for polymode is available.

BUGS    [Toc]    [Back]

     In	order to support polygon fill mode PYM_HOLLOW, IRIS-4D VGX and
     RealityEngine models require that the following conditions	be met:

     1.	  Stencil planes be allocated (at least	one plane).

     2.	  The stencil planes be	initialized to zero prior to drawing hollow
	  polygons.

     3.	  The stencil planes be	used for no other purpose while	drawing	hollow
	  polygons.  (The stencil function is controlled by the	hardware and
	  must not be user specified.)

     IRIS-4D VGX models	have an	error in their microcode that results in
     matching errors between pixels generated by PYM_FILL and PYM_HOLLOW in
     some conditions.  This error will be corrected in the next	software
     release.

     PYM_HOLLOW	is not supported on Impact or Infinite Reality.


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