[Feature Request] Motion Blur Support

[TripleDots]

As seen in the image, motion blur does not affect anything created with the fluids (incl. white water particles.) But it also remove any blur on the moving object whether it's in or behind the fluid.

Tried both CPU and GPU rendering in Cycles but neither worked. It's actually kind of a cool effect.

(The large blobs near the head are shooting up very fast. Even with a 360 shutter angle it's not showing any motion blur.)

Weird thing is that I followed this particle spark effect and it does render motion blur no issues. https://youtu.be/QCMyvcc3ZaU

But I noticed that in the beta test video there is motion blur on a few clips. https://youtu.be/5s7L3ruVaXk
Is that post processing trickery or am I missing a feature here?

Depth of Field however does render correctly on the fluids and with objects in or behind the water as seen here. (Also tested on both CPU and GPU.)

EDIT: it's the same blend file as here #86 but with Susan made a bright orange to show the effect, the cylinder hidden from camera view and black background added.

[rlguy]

Motion blur is not supported at the moment. It's something that we really want to be able to add but we haven't found a way to pass velocity data into Blender Cycles from an addon so that motion blur can be rendered. In the video, motion blur was added in post-processing.

At the moment, I think the most likely way to get motion blur support would be to add a feature to export to an alembic cache and attach the velocity data. But I think this still needs to be implemented in Blender. There is a Blender issue (D2388) discussing this, but it looks like no one is working on it at the moment.

I have converted this issue into a feature request/discussion. If anyone has any ideas/tips for how to add motion support, please let us know!

[vmxeo]

Speed Vector passes with Vector Blur is another route for motion blur.

Not sure there's a direct way of accessing that from an addon. There may be some indirect ways, it'd be a kludge though.

[TripleDots]

I am not at all a programmer so please excuse my basic questioning, but how is cycles rendering their internal fluid system?

(Video of the internal fluid sim with motion blur.)
https://youtu.be/m2yYzhp54qk?t=8s

Also, what you could do is how people force motion blur in compositing for now which is basically layering older frames with 50% opacity. But to do it correctly fluid should be rendered separate so that this only effect fluids and things behind the fluid. If possible with sub frames. Else you get nasty looking motion blur on fast moving objects. IIRC After Effects uses their optical flow(?) technique to create subframes from already existing one. But in the 3D world you could actually generate these frames required. which in theory should look better.
This will probably not help with developing the fluid sim but it might help with working around it in compositing and/or writing a separate plugin.

[vmxeo]

@TripleDots There's a good explanation of motion blur and Blender's internal fluid system here: http://adaptivesamples.com/2016/07/23/motion-blur-dynamic-meshes-cycles/

It also explains why it's not always so straightforward to do on deforming meshes. Other rendering engines also let you render out a separate vector speed passes or AOVs for implementing motion blur later in post, but I haven't found a good way to do that with Cycles for dynamic meshes.

[RevDr]

Would setting per vertex colors of the mesh to the velocity values work?

If so, (I think) these could be used within cycles: get the vertex color and transform into camera space. This image could possibly then be used to do a 2D motion blur.

[juangea]

EDIT: Ok, this was already named by Ryan so... silly additiona by my part :P

Allow me to put a note here that can help a bit with Motion Blur.

In the fracture modifier build the new remesher has now motion blur enabled, I´m not sure if they used this patch or not, but we were talking about it and I think this helped them to enable motion blur in the remesher:

https://developer.blender.org/D2388

This patch is to add motion blur to Alembic caches with variable vertex count meshes, I´m not sure why is not in master, I assume it has not been reviewed and studied enough.

Cheers!

[juangea]

But RLGuy, this has been already implemented by Scorpion81 in his Fracture Modifier branch, so maybe you can implement it here too, I don't think he modifier Cycles at all, I think he did something to his meshing system, but I think you can do this too since Cycles supports motion blur for fluid meshes and such things, it's just a matter of the information your mesh has and how it presents it to cycles, I think that, but please discuss this with Scorpion81 because he knows how to do this.

Cheers!

[DerFluep]

Hey RLGuy, the new Version of DualSPhysics is out with Blender support only for rendering but with Motionblur support:
https://github.com/EPhysLab-UVigo/VisualSPHysics
They use animated Shapekeys to deform the Surface within +/- 1 frame. So Maybe Shapekeys are the way to go?

[rlguy]

Thanks for the tip, I only just learned what shapekeys were just now! I just tested out some scripting for manipulating the shapekeys of an object and it works and renders with motion blur. This definitely seems like the way to go to get motion blur rendering for the fluid surface!

[rlguy]

Motion blur support for the fluid surface has been added in version 1.0.3 (now available). See this document for more information on the status of motion blur rendering for the surface and whitewater: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Motion-Blur-Support