motion blur not being utilized, appears correct at random times.

[guitartom47]

System Information

**Blender Version (including hash):**2.79b f4dc9f9d68b and 2.79 5e5f2ead437 (old daily build)
**FLIP Fluids Version:**1.0.4
**Operating System:**Windows 10
**CPU:**intel core i7 5960x
**GFX:**GTX Titan X
**RAM:**G.Skill F4-2800C15-16GRKD

Describe the bug

The fluid motion blur in the attached frames is sometimes apparent - (frames 10, 12,14,16,17,etc) and sometimes not (11, 13, 15, 19, 21, etc. ). All stills were rendered on the same PC. Motion blur on objects in the scene apperars as normal. As expected, there isn't motion blur for the white water particles.

To Reproduce

Following is a link to the blend file and stills: https://1drv.ms/f/s!AuL_h2DNeOJch-1G2w1W6fqjqKMgAw

Expected Behaviour

I expected Blur on the surface object.

Actual Behaviour

Sometimes it's there, sometimes not.

Screenshots

included in the link

[rlguy]

Hi guitartom47,

Thanks for the report and attaching the screenshots/blend file!

We have had reports that motion blur on the fluid surface is being skipped randomly when rendering with Cycles. Using the workaround of setting the Render Display to Full Screen has fixed the issue for other users and improved the stability when rendering with motion blur: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Scene-Troubleshooting#blender-often-crashes-suddenly-or-does-not-apply-transforms-while-rendering

Does this workaround work for you, or are frames still often rendered incorrectly? If you re-render one of the incorrect frames, is it always missing motion blur, or does it sometime re-render correctly?

- Ryan

[guitartom47]

The workaround doesn't seem to work (with just one try so far) and I notice that the same frames are 'blurred' or unblurred. I have noticed that there may be more 'unblurred' images with higher resolution bakes. (I tried a quick bake at 150 resolution and all 50 frames had good motion blur) Also the motion blur seems to be better at the beginning of the scene and then taper off - perhaps as the scene gets more complex (?). I'll try rebaking next to see if there's a change. Also I'd like to try the higher resolution scene with white water turned off to see if that has any effect. I'll post any results here.

[rlguy]

Hey guitartom47,

I am wondering if rendering from the command line would result in a more stable render. I have just added documentation for how to render from the command line here: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Rendering-from-the-Command-Line

- Ryan

[guitartom47]

Thanks, Ryan! I'll give it a try.
I've been trying different things and so far I've discovered that if I render twice from the same bake, the blurred vs non-blurred images are all the same. Different bakes seem to cause differences in which ones are blurred or non blurred though! Also there are still problems even with white water off. This is all at 300 resolution or higher. 200 resolution was completely correct. I haven't tried any resolutions between 200 and 300. Also I was worried that because I use daily build so often that maybe that was the cause, but it's the same with 2.79b.

Is the latest download from Blender Market correct? The file name for it is 'a4e63c8b97ab9006f83f13e7212843be' and it doesn't read as 1.0.4a in the user preferences. It seems right otherwise though, as far as the mesh.

I'll try the command line solution and post my result here.

[guitartom47]

Well I tried. My files are on a network drive and I'm not sure how to get there.

Also, in a related project, I'm turning up a "OSError: exception: access violation reading 0x000001AABE87D008" while trying to bake a MASSIVE project. It's the same thing but with a boat hull for a wake. I really wish I could back things up just one frame and try over. I've tried skipping and forcing to no avail. This one took a week or so to bake and I just don't want to go back to the beginning.

[rlguy]

Hey guitartom47,

Is the latest download from Blender Market correct? The file name for it is 'a4e63c8b97ab9006f83f13e7212843be' and it doesn't read as 1.0.4a in the user preferences. It seems right otherwise though, as far as the mesh.

The latest download should be the correct version. We found that Blender does not allow putting the 'a' int he version number, so it is left as 1.0.4 and we will change the way we increment a version next time to avoid the confusion.

Well I tried. My files are on a network drive and I'm not sure how to get there.

I do not have access to a network drive right now so I could be wrong with this:

You might be able to access a file on a network drive with the path \\ServerName\SharedFolderName\path\to\file.blend

To get a list of network drives mapped to your computer (server names and folders), running the command net use in CMD might work.

Also, in a related project, I'm turning up a "OSError: exception: access violation reading 0x000001AABE87D008"

That does look like a massive simulation, and might be larger than anything we have tested! It is possible that the error is related to the simulator generating very large files and the addon not being able to open files this large. You simulation might still be recoverable, however!

When does this error happen? Was it after simulating many frames? Was it after pausing and then trying to resume the simulation?

Is there any more information on where this error occurs? The full error message can be be found by opening the Blender system console (Blender > Window > Toggle System Console).

To make sure the cache does not become corrupt during testing, I would suggest making a backup of the cache_directory/savestates/autosave directory:

This directory stores the data of the last frame that is used to resume a simulation. If the autosave becomes corrupt during testing or you want to resume from the original frame, you can replace the autosave directory with the backup.

Hope I can help with this error!

- Ryan

[guitartom47]

Ryan, thanks so much for your advice. I think probably the reason for the 'crash' on the new project is that the file sizes were becoming huge. My PCs (smallest RAM 32 gb) were still able to handle the renders, except that I had to diminish the white water particles to do it. I'm still learning. Additionally, I noticed that with the new Steamboat test, all the blur was rendered (except of course for the white water). I don't know why the original test didn't work properly - but the workaround may be to just redo all the fluid items or create a completely new blender file.

I've redesigned the scene (resolution 1254!! Fluid size still unconvincing, but lots of spray makes it real) so that it won't be so huge and it needed some setting changes anyway. Hopefully it'll still be usable all the way through. (to answer your question, it had been rendering and then just stopped - with the error code).

This project was actually inspired by two things. One was a recent trip to a local steamboat museum, and the other was the recent Artell Blender Dolphin scene that you posted on Facebook. If you look at my original posted image, you'll see that it has an ocean modifier displacement. There's no reason that the ocean modifier displacement textures can't be extended beyond just the domain (I've done it as a proof of concept!) - perhaps to make a river or ocean scene!

Last thing: I rendered everything up to the last frame possible at 100 samples (without the ocean waves): https://www.youtube.com/watch?v=Nhxkkfijbcg

Flip fluid is so cool. You should be deeply proud of your work.

[rlguy]

Thanks! I am very proud, and it is great to see all of these simulations produced with the FLIP Fluids addon.

I am not sure if this applies to your scene, but we recently found out that the 'full screen' rendering workaround might not work if the Blender instance is run with multiple windows: #391 (comment)

Let me know if you run into any more errors. We're working on redesigning how the simulation cache files are organised. Part of this new design will improve how large files are written/read.

Your tests are looking AWESOME, and that's great to know about the ocean modifier displacement technique! I have linked to your tests in this Facebook post and this Twitter post (hope that is alright with you!).

- Ryan

[guitartom47]

Thanks, Ryan! (yes I know this is a very late response. Meant to say this much earlier) Always feel free to link to my stuff, such as it is.

[guitartom47]

A quick PS: Ryan, you might be interested in this: https://youtu.be/IYbkofafILU

Using the Artell Blender Dolphin scene technique and a few other things, I have been able to finally create a scene that could adapted for a river or an ocean - where the FLIP domain blends seamlessly with the ocean modifier and the body of water extends WELL beyond the boundaries of the domain. I did use the ocean modifier foam as well. It's not bad but it needs a little work. This is a 1000 resolution scene.

While I was rendering this I used three computers. One of the computers (with an AMD cpu) decided that it didn't want to render the white water. My easy solution for this in the past has been simply to disable the white water and then turn it on again - problem solved. This scene, however presents a new challenge for the Flip fluid addon. While particle size and materials remain stable, it doesn't keep all the modifiers and the vertex group in memory. Would it be possible to make this a feature? (thinking about this, it's possible that it does already - I've noticed different daily builds behaving oddly)

Also on my wish list, as always, is wind effect on the white water and motion blur for the white water. I'm sure solutions for those will present themselves in time.

If you're interested, here's a link to download the original video: https://1drv.ms/v/s!AuL_h2DNeOJch-5I-Pevxa71MSzM_A

[rlguy]

Hey guitartom47,

This is a fantastic demo! Would it be okay with you if we uploaded the video to our Facebook page and Twitter account? If so, let us know how you would like to be credited (social media links, website, etc).

While particle size and materials remain stable, it doesn't keep all the modifiers and the vertex group in memory. Would it be possible to make this a feature?

I think I know why this happens. This data is stored in the Blender mesh data (Blender > properties > data). In the addon when loading a new frame, the fluid mesh data is deleted and then recreated with the updated mesh. This will removed any user data attached to the mesh data. I'll look into this and see how we can keep these settings persistent between frame.

Also on my wish list, as always, is wind effect on the white water and motion blur for the white water. I'm sure solutions for those will present themselves in time.

We do plan to add support for Blender force objects in the future. I have though about this application before and it would be awesome to have forces affect the whitewater as well as the fluid.

• Ryan

[guitartom47]

Yes of course! As far as I'm concerned you are free to link to my Flickr and Youtube as in the past. If it's easier, you don't even need to ask. This is an image of the steamboat (only partially textured I'm afraid) which we partially see in all these tests btw.

[rlguy]

I will be closing this issue to clean up the issue tracker. If you have any further updates, feel free to comment (here or in the motion blur discussion) or send us an email at flip.fluids@gmail.com.