Mograph Cache Slowing Render Times

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  03 March 2013
Mograph Cache Slowing Render Times

I've been working with a very large dynamics sim, which took about 20-30 minutes to bake into a mograph cache that's about 900 mb. Not a problem though, I was expecting a large size.

What is an issue are my render times, or I should say my 'Preparing' times. I'll place my viewport head 100 frames into the animation, wait for the geo to appear in the viewport, then hit render. For the first 3 minutes 30 seconds, it "Prepares"; then the geo loads for about 5 seconds, followed by one minute of rendering.

Now, if I go back to my scene, go to frame 100, click my cloner and hit the C key to convert it to a series of instances (and thus removing the cache), it takes only 15-20 seconds to prepare, following by the minute or two of rendering.

Any idea as to why this occurs, or thoughts on how to fix it? I've thought about purchasing Nitrobake for such a thing, though I'd like to know if it would fix the problem before spending the cash.

Thanks,
Luke
 
  03 March 2013
Sounds strange, the caching should be eliminating much preparation time. The fact that prepare time is so longer for a later frame means C4D is calculating something over time.
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Kai Pedersen
 
  03 March 2013
After caching--have you disabled the effectors, dynamics, anything that would normally be contributing to the mograph effects prior to caching?
 
  03 March 2013
This guy seems to have the same issue:

http://forums.creativecow.net/readpost/19/880551
 
  03 March 2013
Originally Posted by JoelOtron: After caching--have you disabled the effectors, dynamics, anything that would normally be contributing to the mograph effects prior to caching?


Ooh; That cut the prepare time down to a minute. I didn't think those tags staying enabled would cause an issue like that. Thanks!
 
  03 March 2013
they are still trying to calculate for each frame to get to the final result, the cache just wins over them.
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Quote: "Until you do what you believe in, how do you know whether you believe in it or not?" -Leo Tolstoy
Kai Pedersen
 
  03 March 2013
Originally Posted by LukeLetellier: Ooh; That cut the prepare time down to a minute. I didn't think those tags staying enabled would cause an issue like that. Thanks!



Once you've cached, then the info is stored in the cache tag--you no longer need the effectors, etc. All that info is still being evaluated each frame if its not turned off.

Glad it helped. I've been guilty of missing that occasionally.
 
  03 March 2013
Hi there,

Basically the same problem is happening to me. Except when using Hair. I've cached out the hair dynamics but it still takes ages to "prepare" in the picture viewer. There are no forces left in the scene and the cache works perfectly in the viewport but for some reason it gets ignored at render time. Any ideas?

Thanks!
 
  03 March 2013
are you sure it is saying preparing scene? Hair has to generate the actual hairs between each guide. So is it "preparing" or is it "preparing hair", two very different things. the only way to reduce the preparing hair at all is to cache the dynamics at the hair level instead of the guide level but that takes ages and builds enormous caches.
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Quote: "Until you do what you believe in, how do you know whether you believe in it or not?" -Leo Tolstoy
Kai Pedersen
 
  03 March 2013
Thanks for your reply. Yes it's displaying "Preparing" and not "Preparing hair". It must be related to the dynamics because on frame 0 it doesn't take any time preparing and then goes up with each frame up to 5 minutes at frame 60 for example.

Also there aren't that many hairs in the scene, only about 15000 so it only spends a couple of seconds actually "preparing hair". The dynamics is only a turbulence to give it a windy motion to the grass.

Last edited by ChrisCorr : 03 March 2013 at 09:39 PM.
 
  03 March 2013
I'm talking under correction here but I don't think this is abnormal. My scenes are usually packed with cached sims and also take time to prepair if I want to start rendering deeper into the animation. However, the sims in my scenes usually take hours upon hours to chache in full and the 2-3 minutes it then takes to get to that frame during render seems very fair to me. I've tried it "un-cached" and then it takes much, much longer. I've found that, if you play the animation in your view port, that would be approximately the time it would also take to prepair during render.
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  03 March 2013
It takes pretty much the same time cached or not cached to render that frame in the middle of the animation.

Would you say that when I actually render the whole thing starting from frame 0, the preparation time will be appropriately distributed during render? Or will it still take 5 minutes in those later frames, even though it already rendered the previous ones?

Hope I'm making myself clear. Thanks!
 
  03 March 2013
When you render from frame 0, it only has to do the calculations for that frame so it will obviously take almost no time to prepair. The good news is that, even if you start on a later frame, it will only do the long prep once and then a frame-to-frame prep from there on. I've rendered mostly stills but that's how the few animations I've rendered, has worked.
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Software Used:
3D: Cinema 4D, MotionBuilder
Finished Work:
 
  03 March 2013
Great, thank you. When I saw that long prep time I panicked but it's actually intuitive that since I will be rendering from frame 0 I won't really have those prep times across the final render. That only happens because I'm trying to preview a frame in the middle and it has to simulate up to that point, after which it would - as you said - continue normally without prep time.
 
  03 March 2013
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