AWS Thinkbox Discussion Forums

Where are the channels?


I am trying to figure out how to set some emission velocity on my particles. I thought I might be able add the face normal channel, and then in the BIRTH magma, set that to the particles velocity. However the face normal doesn’t show up in the list of available channels.

What am I missing?

  • The Channel list under the Distribution Sources lists the channels that a particle could acquire from its distribution source and save to disk. When you check Normal and FaceNormal, they will become visible to the Birth and Per-Step Magmas and can be used to set the other channels.
  • In the Magma, you can type in ANY channel in the Input Channel name field - the list underneath is for convenience only. So if you type in FaceNormal and the channel exists because you checked it under the Distribution Sources, it will be used.
  • In the Per-Step Magma in a Stoke Particle Simulator, you must set the AdvectionOffset value to make the particles actually move. The Velocity channel can be set separately to have the actual motion blur / vector display look right, but it can be controlled independently.
  • If you don’t set the AdvectionOffset channel, the particles will show a Velocity, but will not move
  • The AdvectionOffset value is in units per step, while the Velocity is in Units Per Second. So if the Magma is evaluated once per frame, and FPS is 30, the Velocity value must be set to 30x the AdvectionOffset value to produce the expected motion blur.
  • If you set the values only in the Birth Magma, the Velocity will be reset to 0.0 on every step (or will have whatever value came in from Velocity Sources in the sim), so the Per-Step is what you need to use to set both AdvectionOffset and Velocity to keep stuff moving and blurring right.
1 Like

Thanks for this information Bobo, very helpful!
I’m not sure I would have got there myself :smiley:

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