scrbox(3g)

NAME
     scrbox - control the screen box

C SPECIFICATION
     void scrbox(arg)
     long arg;

PARAMETERS
     arg   Expects one of the symbolic constants:

           SB_RESET:  initialize screen box limits and disable the updating of
           screen box limits. (default)

           SB_TRACK:  track scan-converted geometry and characters and update
           the scrbox limits accordingly.

           SB_HOLD:  disable update of screen box limits; hold current values.

DESCRIPTION
     scrbox is a dual of the scrmask capability.  Rather than limiting drawing
     effects to a screen-aligned subregion of the viewport, it tracks the
     screen-aligned subregion (screen box) that has been affected.  Unlike
     scrmask, which defaults to the viewport boundry if not explicitly
     enabled, scrbox must be explicitly turned on to be effective.

     While enabled (mode SB_TRACK) scrbox maintains leftmost, rightmost,
     lowest, and highest window coordinates of all pixels that are scan
     converted.  Because scrbox operates on the pixels that result from the
     scan conversion of points, lines, polygons, and characters; it correctly
     handles wide lines, antialiased (smooth) points and lines, and
     characters.  Because scrbox operation may preceed the framebuffer, scan-
     converted pixels may update the screen box regardless of their Z compare,
     WID compare, or stencil compare results.

     scrbox results are guaranteed to bound the modified framebuffer region,
     but they may exceed the bounds of this region.

     scrbox results are not affected by calls to clear, zclear, sclear, or
     czclear.

     When reset, the leftmost and lowest screen box values are set to be
     greater than the rightmost and highest values, and the updating of screen
     box limits is disabled.

SEE ALSO
     getscrbox, scrmask

NOTES
     IRIS-4D G, GT, and GTX models, Personal Iris, Impact, and Infinite
     Reality, do not support scrbox.  Use getgdesc to determine whether scrbox
     is supported.