zdraw(3G)							     zdraw(3G)

NAME    [Toc]    [Back]

     zdraw - enables or	disables drawing to the	z-buffer

C SPECIFICATION    [Toc]    [Back]

     void zdraw(b)
     Boolean b;

PARAMETERS    [Toc]    [Back]

     b	 expects one of	two possible values:

	 TRUE enables drawing of colors	into the z-buffer.

	 FALSE disables	drawing	of colors into the z-buffer.

DESCRIPTION    [Toc]    [Back]

     When zbuffer is TRUE, depth values	are drawn into the z-buffer as a side
     effect of drawing to the front or back bitplane buffers.  When zbuffer is
     FALSE, however, it	is possible to treat the z-buffer as a third color
     bitplane buffer.  zdraw enables or	disables drawing of color values into
     the z-buffer.

     By	default, and after each	call to	gconfig, zdraw is FALSE.  All
     combinations of values for	backbuffer, frontbuffer, and zdraw are valid
     while the normal framebuffer is in	double buffer mode.  While the normal
     framebuffer is in single buffer mode, backbuffer is ignored, and
     frontbuffer can be	disabled only while zdraw is enabled.

     Because only the normal framebuffer includes a z-buffer, zdraw is
     significant only while the	normal framebuffer is enabled for drawing (see
     drawmode).	 zdraw should not be called while drawing to the overlay,
     underlay, or pop-up framebuffers.

SEE ALSO    [Toc]    [Back]

     backbuffer, drawmode, frontbuffer,	gconfig, zbuffer

NOTE    [Toc]    [Back]

     On	the Personal Iris and Iris Indigo, calling zdraw(TRUE) selects the zbuffer
 as the destination of the pixel writing routines:  writepixels,
     writergb, rectwrite, lrectwrite, and rectcopy.  Geometric drawing
     routines (lines, polygons,	etc.) cannot draw into the z-buffer even when
     zdraw is enabled.	These commands will continue to	draw into the front
     and back buffers (as selected) when zdraw is on.

     On	the Personal Iris, when	zdraw is on it is not possible to write	pixels
     into the frame buffer, regardless of the settings of frontbuffer and
     backbuffer.

     On	the Iris-4D G model, the zdraw functionality is	not supported and the
     routine has no effect.






									Page 1






zdraw(3G)							     zdraw(3G)



     On	all machines, operation	while both zdraw and zbuffer are TRUE is
     undefined.

     When using	zdraw in the colormap mode, the	value written to the zbuffer
     is	the index of the color specified.  For example,	color(2) puts 2's into
     the buffer.

BUGS    [Toc]    [Back]

     On	the Personal Iris, when	zdraw is enabled, geometric drawing commands
     (lines, polygons, etc.) will update depth values into the z-buffer.

     On	Iris Indigo XS24, XZ, Elan and Extreme models, pixel values can	not be
     written to	the normal frame buffer	if the normal frame buffer is in
     doublebuffer mode and zdraw is enabled.

     On	Iris Indigo XS24 and Elan, blendfunction and logicop functions do not
     work while	zdraw is enabled.

     IRIS-4D VGX models	do not support zdraw while the normal framebuffer is
     configured	with stencil bitplanes.	 (see stensize.)

     On	Impact and Infinite Reality zdraw(TRUE)	is not supported.


									PPPPaaaaggggeeee 2222