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How to properly simulate wind effect on smoke

Discussion in 'General Graphics' started by Tony-Lovell, May 14, 2019.

  1. Tony-Lovell

    Tony-Lovell

    Joined:
    Jul 14, 2014
    Posts:
    127
    I find the new Particle System Force Field to be poorly documented.

    With some difficulty, I have found how directionX/Y/Z work (as the documentation does not indicate that directionX/Y/Z is a vector relative to the transform of the game object the PSFF is attached to).

    What else is entirely absent is an explantion of whether the PSFF describes FORCES that cause acceleration of particles under their influence or does it describe a medium velocity or FLOW that the particles enter? That is, if the PSFF is at direction (0, 0, 10) are the particles going to accelerate at 10 m/s^s in positive Z, or are they going to be accelerated such that they will eventually attain a static speed of 10 m/s in positive Z?

    The first would not be a very useful implementation; the second is much more so. Which did Unity deliver to us?

    tone
     
  2. richardkettlewell

    richardkettlewell

    Unity Technologies

    Joined:
    Sep 9, 2015
    Posts:
    2,281
    Hi Tony.

    I am sorry that you find our documentation to be lacking. I have added a clarification to our docs page to explain that forces are applied in the local space of the Force Field.

    Can you provide and explantion of what the second option means? I don't understand it. Although it probably doesn't matter, because our implementation is the first option - the Force Field applies forces to the particles, as the name might suggest. Those forces are then solved via a Euler integration step during the particle system simulation.

    Have you set up anything to test its behaviour? It seems to me that it would probably be trivial to determine how it behaves, especially as we display the min/max particle velocities in the Scene View Overlay when previewing particle systems.

    I'm sorry that you feel this way.

    You would have been welcome to participate in the alpha/beta programs or use https://forum.unity.com/forums/particle-system-previews.129/ where we ran a preview build for many months prior to releasing the feature. Any of those options would have given you the opportunity to contribute to the feature.
     
    Last edited: May 15, 2019
    karl_jones likes this.
  3. Tony-Lovell

    Tony-Lovell

    Joined:
    Jul 14, 2014
    Posts:
    127
    I find that I am deluded somehow. I set up a simple test case and see that particles ARE still able to be influenced by WindZones, but this somehow broke in my app when I upgradfed and the script documentation for WindZone led me to assume that this was by design.

    Please consider: the scripting documentation for WindZone doesn't mention that WindZones can influence particles -- only trees and such. Adding this, and indicating that it works via the "External Forces" module would be great.
     
    Last edited: May 18, 2019
  4. richardkettlewell

    richardkettlewell

    Unity Technologies

    Joined:
    Sep 9, 2015
    Posts:
    2,281
    Thanks for pointing that out. These docs appear to be rather out of date. We are looking at fixing that right now.