View Full Version : Making Slow Motion of a PFlow Animation

Mike Truly
11-09-2009, 02:41 PM
I have dealt with this before but it's been awhile and I'm always wondering if I'm missing something that will make this easier.

I'll use a simplified example. I have an animation setup that goes from 0-100 and this animation also contains PFlow systems. I decide I want to have a 25% slow motion version of this animation.

The easiest way to get a slow motion version setup is to go into the time configuration dialog and set it to 'Custom' and change it from 30fps to 120fps. This changes the overall length of the animation and moves the keyframes proportionally so now all the keyframe animation is setup for a 25% slomo. In PFlow, even the birthing times are adjusted and this is great.

The one area of problems is that if some particles were being emitted upward with a certain Speed and a certain Gravity force back downward... what is the easiest way to adjust these settings to accomodate the slomo? If the speed upward originally was 100, I should set it to be 25... correct? What about the Gravity force setting?

In the end, I need the PFlow action to look exactly as it did in the original animation... only slower.

Thanks for any ideas.

11-09-2009, 02:55 PM
Hi Mike,

I could be VERY wrong but I think the UI of PFlow exposes speed as Units Per Second.
So if your particles were moving at 100 UPS, if you change the FPS from 30 to 120, on frame 120 (one second later) the particles should be EXACTLY on the same spot as with 30 fps, it would have just taken 4 times more frames to get there. So I am not convinced you have to change the speed at all.

Same applies to gravity - changing the FPS changes the TicksPerFrame internally, and PFlow correctly uses ticks to apply influences of forces.

I created a standard PFlow, inverted the speed direction to emit upwards, changed speed to 100 ups. On frame 24 at 24 fps, the first emitted particle was exactly at 100 units away from the emitter (looking at the front view's grid). Switched to 96 fps (4 times more frames), and on frame 96 the first particle was at 100 units from the emitter again. So it took 4 times more frames to get there, but at 1 second time, it travelled the same distance, so speed should not be touched. If you would render at 4 times the number of frames but then play back at the original fps (30, or 24 as in my case), you will get it looking 25% slower.

Then I added a Force + Gravity set to 0.1 and looked at both 24 and 96 fps and the particles reached exactly the same point in space at 1 second regardless of the FPS settings.

If I am missing anything, please let me know...

Mike Truly
11-09-2009, 04:10 PM
Thanks very much for this Bobo! I could have sworn there was some adjustment necessary last time I did this but I must be wrong.

Thanks for straightening me out!

11-09-2009, 04:19 PM
Isn't it possible to do extend video lenght via video post in 3ds max? You can set timeline for "Frames:Ticks" and extend time in video post event. It should work.

I had done teapot bullete time blast (it's in my demoreel 2007, made for glu3d test) with this method few years ago. I am not sure if this technique still applicable in recent versions of max.

11-09-2009, 11:11 PM
Only way I could see any difference occurring is if you had something that depended on a certain integration step...

Mike Truly
11-10-2009, 12:09 PM
Thanks for the ideas folks!

It's been a long time since I used Video Post... so I'll have to look into that route. For some reason, thought VP wouldn't work with PFlow.

Anyway, I'll have to experiment.

Thanks again.

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