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Subframe Sampling
Hi everybody

I've been having some issues getting subframe sampling to work correctly when loading FFX data into a particle flow system.
Essentially, when the particles are generated by the FumeFX Birth operator they don't seem to be subframe sampling and I get little 'puffs' of particles on each frame.
I've tried a bunch of different ideas to get more smooth particle birth with varying levels of success. Probably the most time consuming and what I thought would be the "most likely to succeed" approach was to run the FFX sim with the steps set to 4 so it would calculate the velocities every 1/4 frame. Then in PF, I set the Integration Step to 1/4 frame in hopes that it would utilize the additional subframe data. This idea had no success. It took 4x longer to sim and 4x longer to render the exact same "puffy" result.

A more 'brute force' approach was to make use of a speed operator and an age test to fire the particles out in random directions for one frame after they are born and then feed them to the Fume Follow operator. This was more successful in the sense that I only needed to use the single step simulation and it resolved the 'puffy' emission problem, however all the really cool swirling FFX motion starts to get lost/fuzzed out by the random speed.

Anyway, I can probably send a sample scene if that would help. It's basically an elongated sphere that's spinning and traveling on a path while it emits smoke. I simulate it with velocity and temperature added to the exported channels. Then using FumeBirth and FumeFollow operators in PFlow, I load particles and render them.

- Conrad
I moved here from Canada, and they think I'm slow, eh.
Hello Conrad,

Can you make that particles have initial velocity in the direction of object motion ? That might fix things a little bit.

Hi Kresimir

Sorry for the very late reply and thanks for the advice.

I have been using a variety of different methods to give the particles a little bit more variation in velocity, including both 'Speed by Surface' and a 'Position Object' operator with the particles inheriting some of the emitter motion. Both of these methods work, but they have the side-effect of reducing the visual effect of the fume sim on the initial particle positions. The 'streams' that I was hoping to see coming from the particle based emitter start to look less like little puffs on each frame and more like streams but they also lose the fine detail that is produced in the FFX simulation....so it's a trade off.

The most successful attempt thus far has been accomplished by removing the FFX Birth operator entirely. Since my source in the simulation was a ParticleSource, I just spawn new particles from the same particle system that was simmed. Then the spawned particles are fed into the FFX Follow operator and they get the necessary velocity information from the fume sim. It works, but I'm curious if there is a subframe sampling bug when simulating ParticleSource objects in FFX.

I moved here from Canada, and they think I'm slow, eh.

We will take a look if we can do something about the subframe sampling.
Thank s for your post.



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