zdraw(3G)

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

FORTRAN 77 SPECIFICATION
     subroutine zdraw(b)
     logical 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 zbuffe is  .TRUE., depth values are drawn into the z-buffer as a
     side effect of drawing to the front or back bitplane buffers.  When
     zbuffe 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 gconfi, zdraw is  .FALSE..  All
     combinations of values for backbu, frontb, and zdraw are valid while the
     normal framebuffer is in double buffer mode.  While the normal
     framebuffer is in single buffer mode, backbu is ignored, and frontb 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
     drawmo).  zdraw should not be called while drawing to the overlay,
     underlay, or pop-up framebuffers.

SEE ALSO
     backbu, drawmo, frontb, gconfi, zbuffe

NOTE
     On the Personal Iris and Iris Indigo, calling zdraw(.TRUE.)  selects the
     z-buffer as the destination of the pixel writing routines:  writep,
     writer, rectwr, lrectw, and rectco.  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 frontb and backbu.

     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 zbuffe 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 stensi.)

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