One thing that Mark Harris' clouds considered was lighting I believe.
Portions of the cloud that were shaded were darker and portions of the cloud
most exposed to the sun light were lighter. I don't know the exact
algorithm, but I believe he was doing some extra work with lighting. Then
all of that was cooked into an imposter. I think our current clouds if they
had slightly better textures and smoother alpha blending would look pretty
good. But there's always more than can be done. :-)
Curt.
On Mon, Nov 10, 2008 at 9:15 AM, Manuel Massing wrote:
> Hi Roman,
>
> > I played with 3D clouds patch in my sandbox and forgive me if I'm not
> > familiar with whole flightgear/simgear system.
> > Now I try modify existing code of 3Dclouds to pointsprite usage.
> > Roman
>
> I am not sure point sprites are a good solution here...
> Altough they're put to good use in small-scale particle systems with
> high vertex counts (e.g. something like Mark Harris' cloud rendering),
> they're
> probably not so well suited for this implementation (based on Niniane
> Wangs'
> Paper, AFAICT), where clouds are modeled at a somewhat coarser scale. For
> example, point sprites are clipped like points (at least according to
> spec),
> so billboards will pop into/out of view as the center vertex crosses the
> viewport.
> Perspective-correct point size scaling is possible by fiddling with the
> point
> size attenuation, but still the billboards are constrained to be square and
> to
> be aligned with the imaging plane, so we would loose some flexibility in
> modelling the clouds.
>
> I think the current system would be better optimized by using impostors,
> because performance is probably impacted more by pixel throughput than by
> geometry (which btw might perform better by using arrays instead of single
> quad draw calls in CloudShaderGeometry.cxx).
>
> Would be interested in your benchmarks anyway - what I said being mostly
> theoretical :-)
>
> Manuel
>
>
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--
Curtis Olson: http://baron.flightgear.org/~curt/
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