Manipulating RF cache framespeed

Pontus
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Manipulating RF cache framespeed

Postby Pontus » Sun Dec 27, 2009 12:33 am

Hello ppl, I'm doing a highspeed sort of job where a glass of wine is supposed to get tipped over, splash out and slow down during the action. The action starts att 25 fps and slows down and stops at somewhere around 500 fps.

So for my perdicurment, I know I can change the framesoutput speed in RF, I dont mind as much doing a highframerate simulation, as the sim isnt really that heavy compared, what I do mind is doing a say 5000 frames render, when what I in fact want is 375 frames, and then speed it up in comp to get the result I want.

I would like to bring in the cache into maya and retime it and export a new cache wich includes the speedchange, and then render that with the RFRK.

Assuming someone understands my jibberish is this possible in some way?

Ive seen ppl here discuss the option of changing the framesoutput, stopping a bunch of times and adjusting but that seems a bit unpredictable, I suppose you could set a batch script that runs a bucketload of different scenes at different framesoutput speed that all fill the same .bin sequence, but that doesnt sound fun either. Does anyone know if this sort of thing could be scripted? Ive looked through the scripting reference but it doesnt seem to include calls for the framesoutput...

So any suggestions? .. :D


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bitSeq
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Manipulating RF cache framespeed

Postby bitSeq » Mon Dec 28, 2009 4:26 pm

Hi Pontus, I would sim at 500fps and then when you render only render every 20th frame for 25fps and then just adjust the Nth frame render number halfway through, you can then ease the speed in your video editor.

Cheers

Pontus
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Manipulating RF cache framespeed

Postby Pontus » Tue Dec 29, 2009 7:24 pm

Hmm... I guess, but I want a gradual speed decrease from 25 fps to something like 1500/2000 fps. I guess if I was more of a mathmatician I could construct some kind of script to pick out the frames from a sequence simulated at 2000 fps that would give me a new sequence(375 frames) with a smooth slowdown gradient, and maybe also a proper fps value to feed into the fps of RFRK for adequate motionblur. I kind of got it in pseudocode in my head, just got to get hold of a coder to help me make such a script. But anyways thanks for the input. Happy new years!

lukeiamyourfather
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Manipulating RF cache framespeed

Postby lukeiamyourfather » Tue Dec 29, 2009 7:37 pm

Its possible to do on the Maya side when loading in the meshes but they would have to be on integer frames. So it might not be very smooth unless you have a lot of meshes to go between. Another way would be to use something like ICE in Softimage XSI or the Time Blend SOP in Houdini to create a new particle cache that is sampled at whatever rate you want and then mesh that. Cheers!

Pontus
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Manipulating RF cache framespeed

Postby Pontus » Tue Dec 29, 2009 9:01 pm

Ok, so its possible with meshes in Maya? I was planning on doing it with the RFRK but I guess if meshing is a better bet then maybee I should consider it, well my 1600 fps sequence is 6400 frames, do you think that would be enough to get a smooth look?
I havent been using RF for about 3 years but from what I remember I enjoyed the meshing part the least, RFRK seems a much better choice. Maya is what I got so too bad about XSI and Houdini. Thanks for the input. Ill let you know how it goes!

Cheers!

lukeiamyourfather
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Manipulating RF cache framespeed

Postby lukeiamyourfather » Tue Dec 29, 2009 9:30 pm

Pontus wrote: Ok, so its possible with meshes in Maya? I was planning on doing it with the RFRK but I guess if meshing is a better bet then maybee I should consider it, well my 1600 fps sequence is 6400 frames, do you think that would be enough to get a smooth look?
I havent been using RF for about 3 years but from what I remember I enjoyed the meshing part the least, RFRK seems a much better choice. Maya is what I got so too bad about XSI and Houdini. Thanks for the input. Ill let you know how it goes!

Cheers!

I said meshes but my brain is fried right now. Particles would probably work too as long as they are input on integer frames. If the actual frame is say 50 and frame 125.73 is given as input for the particle loader then it'll mess up the velocity information for motion blur, but frame 125 or 126 would work as input. MEL, Python, or Hypergraph trickery could make that happen. Cheers!

EDIT: Or Python in RealFlow could be used to sample the cache and create a sequence of particles at the correct rate which might be more accurate and smooth (allowing fractions of a frame to be sampled).

Pontus
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Manipulating RF cache framespeed

Postby Pontus » Wed Dec 30, 2009 12:14 am

Hmm... yes I agree trickery is the way to get this to work. Problem is Im having trouble defining that trickery into a solution. I guess Im on my own, but the check will be having my name on it when Im done too so I guess thats fair :P. Thanx for the hints dude. Fried brain... are you a vfx artist by any chance? I seem to recognize the syptom ;).

lukeiamyourfather
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Manipulating RF cache framespeed

Postby lukeiamyourfather » Wed Dec 30, 2009 12:55 am

Pontus wrote: Hmm... yes I agree trickery is the way to get this to work. Problem is Im having trouble defining that trickery into a solution. I guess Im on my own, but the check will be having my name on it when Im done too so I guess thats fair :P. Thanx for the hints dude. Fried brain... are you a vfx artist by any chance? I seem to recognize the syptom ;).

Yes, working on Alice In Wonderland right now. :ninja:

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ISurg
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Manipulating RF cache framespeed

Postby ISurg » Sat Jan 02, 2010 5:30 pm

Well, i'm not sure if i understood the situation correctly, but earlier I've done a simulation, which had to slow down. I've used a simple event script. Here's the main idea-

Code: Select all

def onSimulationFrame():
   a = scene.getFps()
   scene.setFps( a +  some_number * some_number )

You just need to adjust multipliers, to get correct slow-down timing for your simulation, and add an "if...", to start the increments just after certain frame.

lukeiamyourfather
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Manipulating RF cache framespeed

Postby lukeiamyourfather » Sat Jan 02, 2010 5:49 pm

ISurg wrote: Well, i'm not sure if i understood the situation correctly, but earlier I've done a simulation, which had to slow down. I've used a simple event script. Here's the main idea-

Code: Select all

def onSimulationFrame():
   a = scene.getFps()
   scene.setFps( a +  some_number * some_number )

You just need to adjust multipliers, to get correct slow-down timing for your simulation, and add an "if...", to start the increments just after certain frame.

That gets you half way there because the substeps are not accessible with Python. So each time the FPS goes higher the simulations will take longer (because its still too many substeps meant for lower FPS). Best way to do it is simulate at the highest FPS for the whole sequence and then make any changes before rendering (like resample the cache) or in compositing. Cheers!


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