bgnqst(3G)

NAME
     bgnqst, endqst - delimit the vertices of a quadrilateral strip

FORTRAN SPECIFICATION
     subroutine bgnqst

     subroutine endqst

DESCRIPTION
     Vertices specified between bgnqst and endqst are used to define a strip
     of quadrilaterals.  The graphics pipe maintains three vertex registers.
     The first, second, and third vertices are loaded into the registers, but
     no quadrilateral is drawn until the system executes the fourth vertex
     routine. Upon executing the fourth vertex routine, the system draws a
     quadrilateral through the vertices, then replaces the two oldest vertices
     with the third and fourth vertices.

     For each new pair of vertex routines, the system draws a quadrilateral
     through two new vertices and the two older stored vertices, then replaces
     the older stored vertices with the two new vertices.

     The quadrilaterals are drawn as though each quadrilateral was an
     independent polygon with vertex order (n, n+1, n+3, n+2).

     If the quadrilateral projects a self-intersecting polygon, its rendering
     will be hardware-specific.  The Graphics Library only guarantees that
     pixels outside of the convex hull will not be modified.

     Between bgnqst and endqst you can issue the following Graphics Library
     routines:  c, color, cpack, lmbind, lmcolo, lmdef, n, RGBcol, t, and v.
     Use lmdef and lmbind only to respecify materials and their properties.

     There is no limit to the number of vertices that can be specified between
     bgnqst and endqst. The result is undefined, however, if an odd number of
     vertices are specified, or if fewer than four vertices are specified.

     By default, quadrilateral vertices are forced to the nearest pixel center
     prior to scan conversion.  Quadrilateral accuracy is improved when this
     coercion is defeated with the subpix command.  Subpixel vertex
     positioning is especially important when quadrilaterals are scan
     converted with antialiasing enabled (see polysm).

     After endqst the current graphics position is undefined.

     See the Graphics Library Programmer's Guide for examples.

SEE ALSO
     backfa, c, concav, frontf, polymo, polysm, scrsub, defpat, shadem,
     subpix, v
NOTE
     IRIS-4D VGX models use vertex normals to improve the shading quality of
     quadrilaterals, regardless of whether lighting is enabled.

     On some systems quadrilateral strips are decomposed into triangles prior
     to shading and scan conversion.

     See the section, "2.1.4 Polygons," in the Graphics Library Programmer's
     Guide for a discussion on the handling of non-coplanar and/or self-
     intersecting polygons.

     See the section, "2.1.6 Meshes," in the Graphics Library Programmer's
     Guide for a discussion on the order of the vertices when a q-strip is
     decomposed into its equivalent t-mesh.

     On Impact and Infinite Reality lmcolo cannot be called between bgnqst and
     endqst