pntsmooth(3G)							 pntsmooth(3G)

NAME    [Toc]    [Back]

     pntsmooth - specify antialiasing of points

C SPECIFICATION    [Toc]    [Back]

     void pntsmooth(mode)
     unsigned long mode;

PARAMETERS    [Toc]    [Back]

     mode   expects one	of two values:

	    SMP_OFF defeats antialiasing of points (default).

	    SMP_ON enables antialiasing	of points.  It can be modified by an
	    optional symbolic constant:

	    SMP_SMOOTHER indicates that	a higher quality filter	should be used
	    during point drawing.  This	filter typically requires that more
	    pixels be modified,	and therefore potentially reduces the rate at
	    which antialiased points are rendered.

     The constant SMP_SMOOTHER is specified by bitwise ORing it, or by adding
     it, to SMP_ON.  For example:

	  pntsmooth(SMP_ON + SMP_SMOOTHER);


     enables antialiased point drawing with the	highest	quality, and
     potentially lowest	performance, algorithm.	 The modifier is a hint, not a
     directive,	and is therefore ignored by systems that do not	support	the
     requested feature.

DESCRIPTION    [Toc]    [Back]

     pntsmooth controls	the capability to draw antialiased points.  You	can
     draw antialiased points in	either color map mode or RGB mode.

     For color map antialiased points to draw correctly, you must initialize a
     16-entry colormap block (whose lowest entry location is a multiple	of 16)
     to	a ramp between the background color (lowest index) and the point color
     (highest index).  Before drawing points, clear the	area to	the background
     color.

     The pntsmooth hardware replaces the least significant 4 bits of the
     current color index with bits that	represent pixel	coverage.  Therefore,
     by	changing the current color index (only the upper 8 bits	are
     significant) you can select among many 16-entry color ramps, representing
     different colors and intensities.	You can	draw depthcued antialiased
     points in this manner.

     The z-buffer hardware can be used to improve the quality of color map
     antialiased point images.	Enabled	in the standard	depth-comparison mode,
     it	ensures	that points nearer the viewer obscure more distant points.
     Alternately, the z-buffer hardware	can be used to compare color values by



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pntsmooth(3G)							 pntsmooth(3G)



     issuing:

	  zbuffer(TRUE);
	  zsource(ZSRC_COLOR);
	  zfunction(ZF_GREATER);


     Pixels are	then replaced only by 'brighter' values, resulting in better
     intersections between points drawn	using the same ramp.

     RGB antialiased points can	be drawn only on machines that support
     blending.	For these points to draw correctly, the	blendfunction must be
     set to merge new pixel color components into the framebuffer using	the
     incoming (source) alpha values.  Incoming color components	should always
     be	multiplied by the source alpha (BF_SA).	 Current (destination) color
     components	can be multiplied either by one	minus the source alpha
     (BF_MSA), resulting in a weighted average blend, or by one	(BF_ONE),
     resulting in color	accumulation to	saturation; issue:

	  blendfunction(BF_SA, BF_MSA);	/* weighted average */


     or

	  blendfunction(BF_SA, BF_ONE);	/* saturation */


     The pntsmooth hardware scales incoming alpha components by	an 8-bit
     computed coverage value.  Therefore reducing the incoming source alpha
     results in	transparent, antialiased points.

     RGB antialiased points draw correctly over	any background image.  It is
     not necessary to clear the	area in	which they are to be drawn.

     Both color	map and	RGB mode points	are antialiased	effectively only when
     subpixel mode is enabled; issue:

	  subpixel(TRUE);


     The size of antialiased points is controlled by pntsize and pntsizef.
     Although point size can be	arbitrarily specified, only a small, hardware
     specific number of	point sizes is actually	supported.  (Refer to the
     pntsize manpage.)

     The modifier SMP_SMOOTHER can be ORed or ADDed to the symbolic constant
     SMP_ON when antialiased points are	enabled.  When this is done, a higher
     quality and potentially lower performance filter is used to scan convert
     antialiased points.  SMP_SMOOTHER is a hint, not a	directive.  Thus a
     higher quality filter is used only	if it is available.





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pntsmooth(3G)							 pntsmooth(3G)

SEE ALSO    [Toc]    [Back]

     bgnpoint, blendfunction, endpoint,	gversion, pntsize, linesmooth,
     subpixel, v, zbuffer, zfunction, zsource

NOTES    [Toc]    [Back]

     This routine does not function on IRIS-4D B or G models, or on the
     Personal Iris.  Use gversion to determine which type you have.

     IRIS-4D GT	and GTX	models,	as well	as the Personal	Iris, Iris Entry,
     Indy, XL, XS, XS24, XZ, Elan and Extreme systems do not support
     SMP_SMOOTHER.  These systems ignore this hint.

     Iris Entry	pntsmooth support is only valid	for color index	mode.

BUGS    [Toc]    [Back]

     Color-comparison z-buffering is not supported on the IRIS-4D GT or	GTX
     models.


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