czclea(3G)czclea(3G)NAMEczclea - clears the color bitplanes and the z-buffer simultaneously
FORTRAN 77 SPECIFICATION
subroutine czclea(cval, zval)
integer*4 cval, zval
PARAMETERS
cval expects the color to which you want to clear the color bitplanes.
zval expects the depth value to which you want to clear the z-buffer.
DESCRIPTION
czclear sets the color bitplanes in the area of the viewport to cval, and
the z buffer bitplanes in the area of the viewport to zval. Multiple
color bitplane buffers can be cleared simultaneously using the backbu and
frontb commands. The screen mask, when it is set to a subregion of the
viewport, bounds the cleared region. Most other drawing modes, including
alpha function, blend function, logical operation, polygon fill pattern,
stenciling, texture mapping, writemask, zwritemask, and z buffering, have
no effect on the operation of czclea. The current color does not change.
Because only the normal framebuffer includes a z buffer, czclea should be
called only while draw mode is NORMAL.
In RGB mode, the cval parameter expects a packed integer of the same
format used by cpack, namely $aabbggrr, where rr is the red value, bb the
blue value, gg the green value, and aa is the alpha value. In color map
mode this parameter expects an index into the current color map, so only
up to 12 of the least-significant bits are significant.
The valid range of the zval parameter depends on the graphics hardware.
When multisample is enabled, and multisample buffers exist in the current
framebuffer configuration in the current drawmode, the minimum is the
value returned by getgco(GCMZMI) and the maximum is the value returned by
getgco(GCMZMA). Otherwise, the minimum is the value returned by
getgco(GCZMIN) and the maximum is the value returned by getgco(GCZMAX).
It is unaffected by the state of the GLCZRA compatibility mode (see
glcomp).
After czclea executes, the graphics position is undefined.
SEE ALSO
afunct, blendf, clear, cpack, getgde, glcomp, logico, scrmas, setpat,
stenci, texbin, wmpack, writem, zbuffe, zclear, zfunct
NOTES
Whenever you need to clear both the z-buffer and the color bitplanes to
constant values at the same time, use czclea. A simultaneous clear will
take place if circumstances allow it. There is never a penalty in
calling czclea over calling clear and zclear sequentially.
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czclea(3G)czclea(3G)
IRIS-4D GT and GTX models can do a simultaneous clear only under the
following circumstances:
o In RGB mode, the 24 least significant bits of cval (red, green, and
blue) must be identical to the 24 least significant bits of zval.
o In color map mode, the 12 least significant bits of cval must be
identical to the 12 least significant bits of zval.
IRIS-4D VGX models always clear color and z bitplanes banks sequentially,
regardless of the values of cval and zval.
On the Personal Iris, XS, XS24, XZ, Elan and Extreme, you can speed up
czclea by as much as a factor of four for common values of zval if you
call zfunct in conjunction with it such that one of the following
conditions are met:
__________________________________________
zval | zfunct
__________________________________________
getgde(GDZMIN) ZF_GREATER or ZF_GEQUAL
getgde(GDZMAX) ZF_LESS or ZF_LEQUAL
__________________________________________
|
|
Iris Indigo, Indy, and XL systems have a 32-bit zbuffer so use
getgde(GDZMAX) to get the maximum z value and getgde(GDZMIN) to get the
minimum z value.
For performance reasons, Elan, XS, and XS24 products do not physically
clear the z-buffer when calling czclea. On these systems, the LSB of the
z-buffer is used as a flag bit to signal that the z-buffer has been
cleared. The 23 remaining bits are used for the z comparison. In order
to physically clear the z-buffer, first call zfunct(ZFALWA), then draw a
polygon whose z coordinates map to the desired z value. To avoid
updating the framebuffer, call wmpack(0) before drawing. Restore the
writemask and z function afterwards.
BUGS
IRIS-4D G models always clear their z-buffers to GDZMAX, regardless of
the value passed to czclea.
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