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jeremydk
03-12-2012, 03:07 AM
Hi

I have seen this on both 10 and 11.

I have some basically static scenes with radiosity and a stream of boxes (5000) made with particle FX where i see render times increase dramatically.

I haven't had time to really test it as i am in the middle of a project.

The frames are almost identical and the first frame of a render is 7 minutes.
A few hours of render passes and render time is now 1 hour/frame.
I stop the render and start the exact same frame that took an hour and it now takes 7 minutes :cursin:

Is this a know issue ? if not, any tip on how i can make a good bug test and what could possibly be the cause ?

thanks

Jeremy

biliousfrog
03-12-2012, 03:21 AM
In case you haven't seen it: http://www.except.nl/lightwave/RadiosityGuide96/#cache

jeremydk
03-12-2012, 03:30 AM
In case you haven't seen it: http://www.except.nl/lightwave/RadiosityGuide96/#cache

thanks, I've been through that article (it's great).

For this scene cache is on with Automatic Preprocess.

Greenlaw
03-12-2012, 04:12 AM
Using radiosity cache in the scene with 5000 animated boxes is most likely what's causing the gradually increasing the render times. The document suggested by biliousfrog explains why.

G.

Edit: Oh, I see you already read it. Nevermind. :)

jeremydk
03-12-2012, 04:18 AM
thanks for your replies

You might be right as the render have stayed on exactly 7:12 on the last 10 frames with cache off. But it doesn't really solve the problem as i can expect flicker without cache......right ?
Furthermore i don't think it's supposed to increase even if i have 5000 boxes and cache on.



Using radiosity cache in the scene with 5000 animated boxes is most likely what's causing the gradually increasing the render times. The document suggested by biliousfrog explains why.

G.

Edit: Oh, I see you already read it. Nevermind. :)

Greenlaw
03-12-2012, 04:25 AM
But it doesn't really solve the problem as i can expect flicker without cache......right ?
Not necessarily. Final Gather with optimal settings should work without flickering or you could brute force it with Monte Carlo. I usually use MC and be done with it but I do spend a bit time time squeezing as much efficiency in the settings as I can before final rendering.

At work, I would likely do the environment and animated blocks in at least two passes for compositing. This way you can use the cache to speed up the environment scene and no cache for the animated objects scene.

Hope this helps.

G.

Greenlaw
03-12-2012, 04:37 AM
Furthermore i don't think it's supposed to increase even if i have 5000 boxes and cache on.
Actually, this will almost certainly increase the time over the course of the render because the cache data gets bigger as new surfaces are revealed to the camera. In other words, the cache data that is loaded into memory is smaller at the beginning of your render and gradually gets bigger by the end, so there is more data to load into memory at the end of the render--with 5000 tumbling boxes in the scene, this could mean a lot more data to load towards the end. At least that's my understanding of how the cache works. It's certainly been my experience with it.

In general, the radiosity cache is meant for static environments where only the camera is moving. Even then, it's mostly efficient when the camera isn't moving too crazily.

G.

Greenlaw
03-12-2012, 04:47 AM
That said, I have used the cache in scenes with crazy motion, but with lower quality settings to get reasonable render times, and then only if I'm confident that motion blur will hide any noisy artifacts.

I guess that's not really helping but I just wanted to point out that there can be exceptions so long as you know what you're dealing with. :)

biliousfrog
03-12-2012, 07:00 AM
Except's article explains why scene render times often increase, as Greenlaw has also explained. One of the things that can cause it, which Greenlaw hasn't picked up on, is the render multiplier not being at 100%.

tcoursey
03-12-2012, 02:44 PM
thought I'd chime in on this. We use Final Gather, interpolated, pretty much default settings. Bake the cache file about 25 frames and then LOCK the cache file, no flickering, ever!

Some scenes won't require 25 frames, some may need every5 frames, others will only need 100 frames. It all depends on what parts of the scene get seen by the camera on those baked frames. As long as, at one point the camera saw the area needing calculations you'll be fine.

Key here is LOCK the cache file. WYSIWYG when rendering final animation, no flickering. We render 1,000's of frames on each project like this, never have issues.:thumbsup:

Danner
03-12-2012, 03:46 PM
Most modern processors will slow down if they overheat, if it's a laptop that is most likely the problem, they overheat very quickly. Have you monitored your temperatures?