zdraw(3G)

NAME
     zdraw - enables or disables drawing to the z-buffer

C SPECIFICATION
     void zdraw(b)
     Boolean b;

PARAMETERS
     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
     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
     backbuffer, drawmode, frontbuffer, gconfig, zbuffer

NOTE
     On the Personal Iris and Iris Indigo, calling zdraw(TRUE) selects the z-
     buffer 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.
     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
     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.