zsource(3G)zsource(3G)NAMEzsource - selects the source for z-buffering comparisons
C SPECIFICATION
void zsource(src)
long src;
PARAMETERS
src expects one of two possible values:
ZSRC_DEPTH, z-buffering is done by depth comparison (default).
ZSRC_COLOR, z-buffering is done by color comparison.
DESCRIPTION
By default z-buffer comparisons are done on depth data. However, in
certain cases, it can be useful to z-buffer by comparing color values,
especially the color index values generated by the linesmooth and
pntsmooth hardware. When the src parameter is ZSRC_DEPTH, the z-buffer
operation is normal. When the src parameter is ZSRC_COLOR, however,
source and destination color values are compared to determine which
pixels the system draws. In this mode, the zbuffer is not updated when a
pixel is written.
A separate zsource mode is retained by each of the framebuffers: normal,
popup, overlay, and underlay. The current draw mode determines which z
source mode is used, and which is modified by zsource.
SEE ALSO
drawmode, gversion, linesmooth, pntsmooth, zbuffer, zfunction
NOTES
This subroutine does not function on IRIS-4D B or G models.
Currently z-buffer operation is supported only in the normal framebuffer.
To insure compatibility with future releases of the GL, make calls to
zsource only while draw mode is NORMALDRAW.
Use zsource(ZSRC_COLOR) for correct anti-aliasing support in color index
mode on Iris Indy and Iris Indigo.
BUGS
IRIS-4D GT and GTX models support zsource(ZSRC_COLOR) only for non-
subpixel positioned lines drawn after a linesmooth(SML_ON) call.
On early serial numbers of the Personal Iris, ZSRC_DEPTH is the only
supported setting for this routine. For compatibility, they accept the
call zsource(ZSRC_COLOR), but it has the same effect as calling
zfunction(ZF_ALWAYS), which turns off z value comparison. This allows the
unrestricted drawing of color values into the front and back buffers and
depth values into the z-buffer. Use gversion to determine which type of
Personal Iris you have.
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zsource(3G)zsource(3G)
IRIS-4D VGX models support zsource(ZSRC_COLOR) only in color map mode.
Stencil operation is undefined in this case.
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