scrbox(3g)							    scrbox(3g)

NAME    [Toc]    [Back]

     scrbox - control the screen box

C SPECIFICATION    [Toc]    [Back]

     void scrbox(arg)
     long arg;

PARAMETERS    [Toc]    [Back]

     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    [Toc]    [Back]

     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,	scanconverted
 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    [Toc]    [Back]

     getscrbox,	scrmask

NOTES    [Toc]    [Back]

     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.


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