Re: Snawfall

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Juan R. Sáenz-Diez (yuri++at++accesocero.es)
Mon, 22 Mar 1999 21:15:25 +0100

Using a texture to accumulate snow on the windshield sounds good, but I would first
look at my rasterization load, since any of those solutions based on texture
mapping a huge polygon with alpha (or alpha in the texture itself) could compromise
these stats, and they use to be the bottleneck themselves. Using a little more App
computing time, I have been able to implement a good effect just by dropping points
(snowflakes) or lines (raindrops) in a post-draw callback without compromising my
Draw time -- I was able to do that because I was not geometry-limited but
pixel-limited and I had some spare App time. Everything was done in a 2D post-draw
callback, and it was the App who was to compute any speed or wind effects, plus
colour due to lighting and fog.

To sum up, I would first look at my stats, and then decide who is going to take the
job. Then, as Brian points, you have several options to choose from.

I hope that helps,
Regards,
Yuri.

Brian Furtaw escribió:

> Depending on how realistic you want this to be you could approach it in
> serveral ways. pfLightPoints could be used to simulate falling snow or even
> driving snow. The fastest implementaion would be something based on texture
> maps.
>
> Perhaps a couple of polygon meshes say 4, which are made up of more than one
> polygon so you can warp the mesh and create wind blown and turbulance effects.
> Then layer the four meshes in front of the driver beyond the windscreen as
> Mario suggested. Apply a texture of snow with an alpha component from a large
> texture map and animate the texture coordinates. Snow driving toward the
> windshield could be added using the pfLightPoints. Turn learn how you could use
> pfLightPoints to implement this see Angus Dorbie's Aqua demo (www.dorbie.com)
> which used pfLightPoints for bubbles.
>
> An animated texture on the windshield and hood of the vehicle could represent
> accumulating snow. Page in texture maps which show more accumulation over time.
>
> Brian
>
> On Mar 22, 5:30pm, MLM Veraart wrote:
> > Subject: Re: Snawfall
> > Michael Plass wrote:
> > >
> > > I want to realize snawfall in a driving simulation application. How
> > > can I do this without a big decrease of draw performance? Is it
> > > possible to use the overlay planes to create animated snawfall?
> > You can use a polygon (quad) in front of the camera/car wind screen
> > and on this polygon you animate (translate) a texture that looks
> > like a snowfall snapshot. For the texture coord animation you can use
> > a pfFlux buffer as texture attribute of the pfGeoSet.
> >
> > Mario
> > > --
> > > Michael Plass mailto:plass++at++philosys.de
> > > PHILOSYS Software GmbH http://www.philosys.de/
> > > Edisonstr. 6 phone: +49 (0)89 / 321 407-21
> > > 85716 Unterschleissheim fax: +49 (0)89 / 321 407-12
> > -----------------------------------------------------------------------
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> >-- End of excerpt from MLM Veraart
>
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