czclea(3G)

NAME
     czclea - 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.
     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.