zbuffer lrectread

[Mike Papper]

I fixed my zbuffer problem. The reason I was getting the "far" values was
because I was "writing" to the zbuffer inadvertently, while drawing
in the POPUP planes with the zbuffer on. (I had been using
a "square magnifying glass" in the POPUP planes of my window
to decide what area of the zbuffer to read.
The initial zclear put in the far values, and as I moved
the magnifying glass, the zbuffer was written to
(there is no zbuffer mode in these planes, so results
are unpredictable).

Note that I did not have to convert my 24 bit integers to 32
(z buffer lrectread values should always have 0s in top 8 bits --
the manual also says this -- haven't tried on a VGX though).
I did not have to use zdraw, only readsource.

The only question I have now iss why zclear doesn't set the zbuffer
to the highest lsetdepth value (it ALWAYS sets it to 16000000 or so).
I ,suspect this is for efficiency, zclear deals with bitplanes
and doesn't look at the rest of the GL state.
Thus even on a GTX with z buffer range 8,000,000 to -8,000,000
zclear gives 16,000,000 (all values approximate).
Subsequent writes to zbuffer (via drawing routines)
does give values within the lsetdepth range.

Mike Papper
mpapp at godzilla.cgl.rmit.oz.au