zdraw(3G)zdraw(3G)NAMEzdraw - 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.
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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
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.
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