polymode(3G)

NAME
     polymode - control the rendering of polygons

C SPECIFICATION
     void polymode(long mode)

PARAMETERS
     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
     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).
     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 scribed-
     surface renderings can be done taking advantage of this fact.

SEE ALSO
     bgnpolygon, endpolygon, polysmooth, stencil

NOTES
     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
     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.