Pre-Roll The Simulation

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Hi everyone,

I was hoping to start simulating my pyro sim 50 frames before frame 1 so there is smoke starting in the scene from frame 1. I assumed wrong that setting the creation frame in the smoke object to -50 would work. Anybody have any ideas how to accomplish this? I know I could shift things over 50 frames but I feel as though I shouldn't have to do that. Also with larger scenes that could be a serious pain to move all the key frames over. Anyways if anybody has any ideas it would be really appreciated. Thank you!

Vincent Griffith
Edited by VGriffith - Oct. 30, 2019 23:01:39
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The creation frame must be before or on the start frame of the dopnetwork. Change the start frame of the dopnetwork to be 50 frames earlier should work, although I'm not sure I've tried using negative frames on a solver start time.
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This is why people traditionally work from 1001… so that if they need pre-roll they can access those previous frames.
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I never had issues with negative frames in Houdini, however it's just not ideal if you have to also cache the negative frames as other softwares don't deal well with such sequences

Starting at 1001 is usually a good idea and we do it too, even though you will loose some precision of $FF and @Frame variables that way and may require workarounds in certain cases like retiming or motion blur, but starting at 1 wouldn't eliminate those problems completely anyway
Tomas Slancik
FX Supervisor
Method Studios, NY
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