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Do we have whirlwinds in SL?


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Bobbie Faulds wrote:

I would say that was a function of the particle script

Yes but the strange thing is I've only seen it once. Usually the smoke from the two chimneys flow in the same direction. SO obviously what happened was that two identical copies of the same script run on the same sim got different readings for wind direction.

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Hmmm. Now that you mention it, how does PSYS_PART_WIND_MASK even work? (and the wind parameter to PRIM_FLEXIBLE?) I'm pretty sure it doesn't cause emitters to send any updates to the viewer. Instead, I suspect the viewer gets regular updates from the sim about current wind conditions; viewers used to make a background wind noise, long ago, and Linden trees could move in the wind.

Anyway, that doesn't explain the smoke. We know llWind() takes an offset parameter, where that offset must be to a point in the same region as the script, hence server-side the wind is intended to be able to vary across the region. Indeed, Andrew mentions (back in 2005-6) a 2-D fluid simulation used to generate the SL weather, including wind.

So yeah, tldr, I think we have whirlwinds.

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SkillsFurrystorm wrote:

It's two fireplaces with particle smoke, rotated 180 degrees because they are at each end of the building. Not exactly rocket science.

No, as I said, this only happened once - usually the smoke from both chimneys go in the same direction. If it had been the rotation of the emitters, they would always have gone in different directions.

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Years ago, I accidentally discovered the magic of the SL Wind. I'm sure many people knew all about it, but I wasn't one of them. Since that time, I watched the magic vanish. Now you've provided evidence that it's back and I just logged in to witness it myself.

One upon a time, and perhaps once again, the SL wind varies in speed and direction across a region. You can see this by enabling Develop->Render Metadata->Wind Vectors. In the sky over your head you'll see red steamers with green heads. The heads are anchored and the streamer points in the direction the wind is blowing, with a length proportional to wind speed.

Here's a snapshot of those streamers taken moments ago...



You can clearly see that the winds are not uniform across the sim (yay!).

Here's a video of a contemplation spot I created years ago after my accidental discovery of this variability...

https://www.flickr.com/photos/58030004@N06/8403826343/in/dateposted-public/

In the opening seconds, you can see that the dandelion seed particles at the top of the screen are blowing in a different direction than those at the bottom. The effect of region wind variability on particles at this scale was simply beautiful. This discovery and my use of it remain one of my favorite accomplishments in my nearly nine years in SL. Several years ago I noticed that the winds had become uniform across the region, destroying the magic in my contemplation spot. That was another of the death by a thousand cuts that has caused me to lose some interest in SL.

As the SL winds are a viewer side function, I imagine there's a debug setting for enabling variabilty across a sim, and perhaps there were releases of the viewer in which that setting had changed. When I next get in-world (don't wait up for me), I'll give you a copy of the contempation spot and some instructions on how to deploy and view it. If you are lucky enough to have a viewer that's exhibiting wind variability across the region, I hope you'll find the effect as enchanting as I have.

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