From: ihawkes2++at++csc.com.au
Date: 11/05/2000 20:11:23
I'm afraid I'm still embroiled in wobble problems! I have focussed on
trying to apply the tex coord offset solution to a single cliptexture tile
(ie to small region of cliptextured geometry which has an associated
pre-cull callback used to set its virtual cliptexture parameters). I
pre-processed the tex coords for this tile by subtracting an offset from
each tex coord. The offset I chose was the value of the tex coord at the
lower left corner of the tile. I then subtracted the same offset from the
clip centre in the pre-cull callback and applied the new clip centre using
"applyCenter". The result is an image that is initially sort of correct,
but as soon as I move the eyepoint (ie the clipcentre), the cliptexture
updates in a weird disjointed fashion (a much worse effect than the
original wobble!). It looks like different levels might be being offset in
different ways.
In order to demonstrate the problem on some common ground, I have updated
the sample program virtcliptex.c so that it produces the same effect when
run with the moffett virtual cliptexture. The original version of the
program displays a cliptexture on a tessellated grid. I have changed it so
that you can specify that only a subset of grid cells be loaded, and you
can specify that the tex coord offset be applied. The additions to the
command line options are:
* -s <size> : size of the grid (default 1000)
* -t <tess> : make a <tess>x<tess> grid (default 2x2)
* -l <tess> : only load a <tess>x<tess> subgrid (default -t value)
* -i <cell index> : start load at cell with given index in grid X direction (default 0)
* -j <cell index> : start load at cell with given index in grid Y direction (default 0)
* -o : use the tex coord offset precision fix
* -e <num> : set num effective levels to num
Note I have updated the pre-cull callback routine (virtCallback) to use my
algorithm for setting cliptexture parameters, but I get the same effect
using the original virtCallback when it is adjusted to do the tex coord
offset.
To demonstrate the effect, compile newVirtcliptex.c and execute using:
newVirtcliptex -s1000 -t10 -l1 -i9 -j2 -o mof_virtual.ct
(which loads up a single tile at position (9,2) on a 10x10 grid)
To turn the tex coord offset off, run
newVirtcliptex -s1000 -t10 -l1 -i9 -j2 mof_virtual.ct
Pressing "v" at runtime will toggle per-frame logging of cliptexture tile
parameters; pressing "g" toggles gridification.
Lines of code of interest are 708 - 738, where the tex coords are
established; and
316 - 388 in the pre-cull callback routine.
Any guidance as to where I have gone astray would be much appreciated!
Thanks,
Ian Hawkes
(See attached file: newVirtcliptex.c)
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