View Full Version : pflow energy threads project (one strange bug with speedbyicon helper, image inside)

06 June 2010, 11:52 PM
Hi, i'm creating a kind of blown out energy effect, it's hard to explain but imagine a glowing wispy smoke effect that would follow a spline and evolve over time, all of it has to be done in pflow with no custom plugs or scripting as it will be rendered on a renderfarm and i have no experience in scripting.

I will be adding all of the glow effects in post, for that i need to render the particles with zdepth, normal, spec, and other custom render elements made for the creation of this effect (i will be using plane shapes with rotation speed space follow node). It will be something different from an ordinary spline follow particle effect, i have few good ideas, but i need help with some technical issues.

I'm using the speed by icon helper to send the particles along a certain path, but the particles dont create a solid path, also, at the end of the animation some of them start appearing randomly in the viewport close to the spline shape. I tried normalizing the spline, changing spline points type etc.

For a competely different solution i was thinking about sending one particle along a path and adding spawn by travel, i will check if that works tomorrow, nevertheless i really want to know what is causing this.

For the secondary effect around the spline i'm thinking about animating some wind space warps along the spline, with certain offset to the left and right side, so that the spherical wind forces would follow the spline movement , and constantly take some of the particles to the sides, i need to achive the effect of the solid energy wave being pulled apart thread by thread by the surrounding in a motion of flame or smoke. Is this a good approach or would you suggest something else?

06 June 2010, 04:03 AM
This is most probably caused by collision of sampling vs. sub-sampling settings in the flow.

By default, the viewport integration is set to One Frame which means that the Speed By Icon operator asks the icon about its velocity only once per frame. But the Birth operator is set by default to Sub-Frame sampling, so it gives birth to particles many times within a frame interval. Their data is interpolated between the previous and the next frame's values but there is no actual data about the real position of the icon at any point in between the two frame samples, so when the integration step calculates the new positions and velocities, you get more and more error the farther the particle is from the real per-frame samples:

If you disable the Sub-Frame Sampling in the Birth operator, you get all particles born only on full frames, and they all get their velocity from that frame too. But that is not enough to build a solid line:

If we reenable the Birth Sub-Sampling and reduce the Integration step to 1/2 or 1/4, the curve gets sampled multiple times within the frame, so the particles born between two samples have a lot more precise data about the actual direction of the icon at that sub-frame point in time:

06 June 2010, 09:51 AM
Yes, it worked, just as always one simple checkbox/list and the problem is fixed, i havent though about searching in the pfsource node, now it seems logical. Thanks

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06 June 2010, 09:51 AM
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