czclear(3G) czclear(3G)
czclear - clears the color bitplanes and the z-buffer simultaneously
void czclear(unsigned long cval, long zval)
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.
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 backbuffer
and frontbuffer 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 czclear. The current color
does not change.
Because only the normal framebuffer includes a z buffer, czclear should
be called only while draw mode is NORMALDRAW.
In RGB mode, the cval parameter expects a packed integer of the same
format used by cpack, namely 0xaabbggrr, 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 getgconfig(GC_MS_ZMIN) and the maximum is the value
returned by getgconfig(GC_MS_ZMAX). Otherwise, the minimum is the value
returned by getgconfig(GC_ZMIN) and the maximum is the value returned by
getgconfig(GC_ZMAX). It is unaffected by the state of the GLC_ZRANGEMAP
compatibility mode (see glcompat).
After czclear executes, the graphics position is undefined.
afunction, blendfunction, clear, cpack, getgdesc, glcompat, logicop,
scrmask, setpattern, stencil, texbind, wmpack, writemask, zbuffer,
zclear, zfunction
Whenever you need to clear both the z-buffer and the color bitplanes to
constant values at the same time, use czclear. A simultaneous clear will
take place if circumstances allow it. There is never a penalty in
calling czclear over calling clear and zclear sequentially.
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czclear(3G) czclear(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
czclear by as much as a factor of four for common values of zval if you
call zfunction in conjunction with it such that one of the following
conditions are met:
_____________________________________________
| zval | zfunction |
|____________________________________________|
|getgdesc(GD_ZMIN) ZF_GREATER or ZF_GEQUAL |
|getgdesc(GD_ZMAX) ZF_LESS or ZF_LEQUAL |
|____________________________________________|
Iris Indigo, Indy, and XL systems have a 32-bit zbuffer so use
getgdesc(GD_ZMAX) to get the maximum z value and getgdesc(GD_ZMIN) to get
the minimum z value.
For performance reasons, Elan, XS, and XS24 products do not physically
clear the z-buffer when calling czclear. 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 zfunction(ZF_ALWAYS), 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.
IRIS-4D G models always clear their z-buffers to GD_ZMAX, regardless of
the value passed to czclear.
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