And I thought joining this mailing list would get me
into something different.....  ;-)

Ray tracing is not ready for real-time flight simulation.
I'm speaking from experience here. I used to be on the
same mailing list as those OpenRT guys. I also wrote the
renderer behind rtChess:

Which BTW, is available for download (the game) and comes
with docs. Be sure you right-click to drag the board
around. Use the Space-bar for options menu. Unlike most
chess games, you can probably beat this one.

I've been working the realtime ray tracing (RTRT) stuff
for years, and it's always been "real soon now" for
gaming performance. My library can easily render as many
polygons as you can fit in RAM at a couple FPS (requires
undersampling) on my 700MHz AMD. It's about 40% faster
now than when we wrote rtChess. As with many things,
there is one tiny piece of code that consumes 90% of the
time and I've worked really hard on that. When I get
around to releasing it (probably GPL) some assembly guru
*might* get a bit more performance out of it.

Because RT is point sampled, the render time is mostly a
function of the number of pixels rather than the number
of polygons. The time complexity is very good WRT scene
size (think log n). A few objects can be handled really
really fast on a modern processor. Unfortunately, using
1000s of objects brings log(n) up to where things are
rather slow. Going to millions of objects just cuts it
in half again. GPUs are not currently able to handle the
data structures and recursive algorithms required to get
scene scalability, nor do they use double precision.

Eric Haines once asked me to estimate when RTRT will be
really feasible - I estimated 2012 and so did he. That
doesn't take into account the brick wall we see now with
power density and no 4GHz pentiums and all that...
Multi-core is great for RT. Multi-threading is one of
the features I need to add (done before but removed)
because it scales nearly optimally with more CPUs.

I could probably (openRT too) load the entire FGFS
scenery database and render it at 1FPS given enough RAM.
Unfortunately that doesn't mean you'll be flying in a
ray traced plane any time soon.


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