Opacity linked to life


Is there a way to link the opacity to the “life” of the smoke?
As far as I know you can only link the opacity to the temperature.
I´m trying to hide the source of the emission, and have the smoke “appear” in the air.

Thank you advance,

Yes, I can think of two options:

Option 1 (TFD)

  • Emit Fuel io. Density from the emitter
  • Activate the Fuel Channel
  • Set the Viewport Preview to show the Fuel channel
  • Adjust Emitter/Fuel Value and Container/Sim/Fuel/Density Emission until the Fuel moves far enough away from the emitter.
  • Set the Viewport to show density again
  • Use the Rendering/Smoke Mapping curve to clip low density values. I.e. move the left knot of the curve from (0, 0) to sth. like (0.2, 0).
  • The density will be emitted from the Fuel plume as if using Add mode on the emitter. The intensity thus fades in over time. At the same time the flow moves the density away from the emitter. The goal is to set the shader mapping curve s.t. the low-density region close to the emitter do not get rendered.

The control through the Fuel channel has its limits though and the effect may be hard to dial in.

Option 2
Reactions has options to control the indirect density generation using a curve instead of a single value. This could make the process more directable. There is also the option to create an actual “Life” channel that might improve control further.
I’ll create an example setup to test this.

1 Like

Hi Jascha

Thank you so much for your reply. I had in mind that solution you mention using fuel and density, I´ll check if that works.

Didn´t hear about Reactions before, nice package, I´ll give that a try!


I finally got around to creating a sample setup in Reactions for this effect. Is this look roughly what you had in mind?

The approach is slightly different. It uses a mask channel with the same source as the density channel but faster decay. The mask is then subtracted from the density to obtain ‘masked density’ which is rendered. By changing the mask decay speed we control the size of the mask plume and thus how far away from the source the density will be hidden.

There are a few possible tweaks and extensions that would make it more art-directable. Let me know if this would be useful to you.