Unusual long render time (smoke simulation)

Hello everyone.

This is my very first post here on Blenderartists and I’m in the need of some assistance.

A few days ago I began a project, doing the Disruptor from the game Command & Conquer Tiberian Sun and I used this image as reference http://vignette1.wikia.nocookie.net/cnc/images/0/05/Disruptor.jpg/revision/latest?cb=20101218012936

Here is my final render https://scontent.xx.fbcdn.net/hphotos-xft1/v/t1.0-9/11140190_10203223361143833_476927017821886990_n.jpg?oh=76ae5f613e20c92ecadd92c9bb5e90dd&oe=562E79FF

Now, doing the dust cloud was a living nightmare. I’m not that good using the simulations and I avoid doing it if possible but that dust added that “extra” to the image.
I used the smoke simulation in an earlier project, also based on Tiberian Sun. https://scontent.xx.fbcdn.net/hphotos-xaf1/t31.0-8/10927842_10202613804865307_7648871000551838943_o.jpg

For the first time I had to use the wind force field in order to get the dust flow up to the right. And I got the effect I wanted. In order to save time I used the same smoke material from the first Tiberian Sun project in this one and it looked nice, I was happy with it.

To render the first project took about 3-4 hours with 1000 samples on the primary render layer.
But to render the Disruptor with 1300 samples took 33 HOURS!

The longest render I’ve ever made took 6 hours.
I know it would take a bit longer to render since I had to use my CPU since I used a smoke simulation but 33 hours?!

I’ve been thinking if it’s because I rendered it with a resolution of 3840 x 3398 but somehow I still find it unlikely.
To render it without the smoke present cuts it down to just 1 hour and then I can render it with my graphics card.

Now, I wonder if I could get some help to locate the reason why it took 33 hours to render.
Maybe it’s an option I’ve activated by mistake, it is because I used a wind force field, is it a material setup?
I’m no expert, I still find Blender quite difficult to use but if I know the reason why, then I can maybe avoid for future projects and renders.

How should I do this? Should I upload my blend file with textures or without or how does it work here?

Thank you

Try uploading but smoke simulations in cycles on the cpu is slow. We’re waiting for GPU support.

Hi, render size has huge influence in render time, if you render your file in HD it would take 1/4 your 33H.
You can upload files after ten post in the forum, use http://www.pasteall.org/blend/ if you file is < 30 MB.
It is hard to say why you have such render times without the file; Include textures if possible.
Welcome to the forum.

Cheers, mib

Hi. Thanks for the quick reply.
So, you’re saying that render it with 3840 x 3398 is the reason why it took so long?
Usually I keep the default resolution but it didn’t work out well with the camera angle.
In a test render, I put the smoke on its own layer but the smoke ended up almost invisible and I couldn’t find a way to increase the opacity or visibility.

I uploaded the blend file but I was given no option to upload textures. http://www.pasteall.org/blend/36554
I can upload files after 10 posts? Hmm. I think it’s going to take a while.
To be honest, I feel extremely uncomfortable participating in online discussions.
Still, I really appreciate your quick reply

Hi, you can pack textures in your .blend.
File menu > External Data > Pack all in your .blend
Will look in to your file tomorrow .

Cheers, mib

Oh, I had no idea you could pack textures into a .blend file like that.
I wish I had that knowledge three years ago. Been running around with USB drives and uploading to Dropbox. And the easiest solution has been in front of me all this time.
Well, better late than never.

Anyway, here is the .blend file with included textures http://www.pasteall.org/blend/36559
However, when packing the textures together, it said the environment texture could not be found but when I’m in render view, everything is where it’s supposed to be.

Hi, I can render this file with 50% Dimension in 06:20.00 minutes with some changes in render settings and smoke material.
It render in 02:17.87 on my GTX 760.
It should be possible to render this file in 25 minutes in full size on my low end i5.
22 hours are incredible except you have a Pentium 4 CPU.
Please add your system specs.
May you can try my edited file with 25% dimension, x8 give you ~100% render time.

CHeers, mib


GDI disruptor_edit.blend (3.57 MB)

I’ve taken a look at your modified version. The only difference I’ve noticed is what you said, half the dimension and some changes in Light Paths. Actually, I have no idea what Light Paths does. I keep every setting I don’t know what it does at default.
You also mentioned you made some changes to the smoke material setup but I can’t find any changes to it.

I did render it just the way you sent it back to me. I enabled the smoke simulation again, re-added the textures and set the sampling to 1200.
Still only 50% in resolution. I never finished the render but it said it would take about 2 hours which is close to my usual render time.
Then I tried 100% resolution and then it said it would take 9 hours. Still, it is a much better improvement than 33 hours.
Could it be the changes in Light paths that could make this huge difference?

“25% dimension x8 give you 100% render time”. I’m sorry, but I do not understand what you mean.

My processor is: i5-3570K 3.40GHz (4 CPUs)
Graphics card: NVIDIA GeForce GTX 760

You can turn off some rays for your objects. For example, does the smoke really need to cast shadows or be visible in reflections, even on diffuse objects? Nope? Then turn those rays off. Your render times will probably be drastically decreased. When I optimized my scene, it rendered in less than 25% of the original time.

After doing the changes in the Render settings as Mib2berlin did and disable all but Camera ray visibilities for the smoke and the blue sound energy wave as Mourlie recommended, and also enable Homogeneous in the Material settings, I managed to cut down the render time to 5 hours and 50 minutes.
I had to enable the smoke’s shadows in ray visibility again though, otherwise I got some weird looking shadows caused by Homogeneous.

From 33 hours to almost 6 hours is an enormous difference and within acceptable render time. I don’t think I can cut it down much more. I’ve already rendered it when it took 33 hours and I’m happy how it turned out. But now I know what settings to look out for next time I’m using the smoke simulation if the render time takes way longer than it should.

I thank you all for your support.