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Smoke follow (fast) animated curve


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Hey Everyone,

i'm hoping someone could help me with this problem.

In a nutshell, i need to move smoke down an animated path, so that it sticks really tightly to the paths animation, but with all the dynamism a smoke sim brings to the table, i.e. nice peeling away around all the edges etc

- I have a fairly fast moving alembic curve - cached out with 10 substeps. (may not be needed but there if i do)

- I am using pops with curve force to fire particles down the path, so they follow the curve closely.

- Then im using the particles to source density, and also adding their velocity into the sim so that it makes the smoke move along the curve. 

- Im using a high dissipation value so that i can tighten up the expansion so you can really get a sense of where the curve is / maintain the shape.


My issues lie generally in 2 places:

1. Where the animated curve is moving the most - the smoke / velocities struggle to catch up and i end up with a hard edge.

2. Where the curve is tangentially facing inwards in relation to the curve, the velocities 'add' the other way, also creating a hard edge.


To try and illustrate what im after - if i could animate a regular smoke sim down a straight path and then warp it into an animated spline shape / spline wrap effect, this would be the best way to achieve it, but im really not sure if is possible - hence this approach.

I have already tried upping substeps - but it didnt make any difference. My gut feeling is that the problem lies within how i am sourcing the velocity. I will point out that i am very much in my houdini infancy, so my ability to problem solve isn't great (yet!)

Has anyone worked on a similar effect before, or does anyone have any tips/tricks/tuts on how to achieve what im after?

Any/All help very much appreciated!








2019-05-27 12_30_59-Adobe After Effects CC 2018 - Untitled Project.aep _.png

2019-05-27 12_30_42-Adobe After Effects CC 2018 - Untitled Project.aep _.png

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Adding a Drag Force to the end of your pyro simulation and enabling and setting a low dissipation value under the Shape tab, helps keep the smoke on the line better.



Edited by Atom
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Another approach might be to skin the line, by placing a circular mesh around it then reference the points of the mesh inside a Gas Wrangle on the velocity update of the pyro solver. This way you can create a custom drag that reduces velocity the farther from the central line, that the smoke travels.

The cage is not a collision mechanism, it merely offers a reference @P for the smoke to compare against.



You will probably need to dial in the distance values of the fit to achieve the best look.

vector p1 = point(0, "P", 0);
float dis = distance(p1, @P);

//Change fit range and resulting values to dial it in.

// Get half as fast, the farther out it travels.
@vel *= fit(dis, 0.5, 1, 1, 0.5);

NOTE: Because the wrangle has no input, the point fetched, from input #0 is actually defined under the Inputs tab (which points to the mesh cage SOP) of the wrangle, this is a little different than standard SOP manipulations of input 0.

Edited by Atom
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@char - Thanks for this (good timing!) I havent had a go with clustering at all yet - ive heard its a bit of a beast to set up and im on a tight deadline, but thanks for the link.

@Atom -  Awesome man, thank you! Really appreciate you taking the time to look through that file, the custom drag method looks really cool, and opens the door for much more directability for other fx. Nice one!

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@bergerac14 Have a look into the file posted in the description of the video, maybe it helps, it's not that complicated to be real honest. I had a look at it and a lot of it made sense, the only confusing bit is setting up the Simulation at the end so I still need to take time to figure it out!

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