Particle flow and vray motion blur.

[trixian]

Hi.
I can't seem to get vray to motion blur my particles. These are instanced geometry objects, and there are usually no more than 50 or so on screen at any given time. Vray seems to blur parts of 2 frames and mixes them on top of each other. Fiddling around with the centre interval seems to have no effect. Changing the geometry to pflow tetra seems to yield no motion blur at all. The deadline is creeping up pretty fast now so any help I can get would be very appreciated. Ill make a mock-up of the scene and post it.

[Adam H. Stewart]

It is working for me

It is working for me using 3ds 7.1, Vray 1.09r. I thought it might be a 3ds thing but I tried 6 and it worked there aswell. I even tested with Instanced geom and everything looks nice a blurry as it should

[vlado]

VRay is not able to produce motion blur if the particles change count inside a frame. To get motion blur for the particles, you need to:

(a) make sure that particles are not born or die inside of a frame (that is, no sub-frame sampling) - this depends on how your particle system is set up.
(b) keep the VRay motion blur interval within a frame (f.e. center at 0.5 and duration 0.9).

If you cannot guarantee (a) for your setup, it might be better to render the particles separately in the scanline renderer, or use Camera effect motion blur.

Best regards,
Vlado

[charleyc]

Is this on the list of things to be addressed?

[trixian]

Well as I have a million things to do, I still haven't managed to make a mock-up of my scene (can't show the original....NDA blabla). If I manage to make pflow not generate particles inside of one frame (as you said), how will the motion blur be on my instanced mesh then. I tried this again with a fresh scene, and it worked, but that was with a simple setup, and displaying the particles as boxes.

[Morbid Angel]

I agree with vlado. As scanline camera multipass is the closest thing to the true motion blur (all tho not exact) it would be most efficient solution if you are pressured by the deadline.

[charleyc]

Also, if you have specific needs of VRay for the instanced particles, another way to achieve motion blur is to render the sequence out of VRay without mblur and then apply the rendered images as a Camera Mapped texture to the mesh with scanline and render your mblur there. This is usually a quicker way to achive mblur as there are less material calulations taking place.

[thedoubtfulguest]

Solution for Vray motion blur with particles

Hi all,

It seems Vray motion blur has a funny "bug" with particles. I couldn't figure out why motion blur sometimes worked and sometimes didn't, or gave the error "Object PArray01 has changed topology, can't motion blur mesh deformations" This is what I found...

Basically you have to have the same number of particles in a scene from one frame to the next. This is because vray cannot motion blur 99 particles into 100 or however many you have.

So if I have a scene with particles with a life of 100 and rate of 1 starting to spawn at frame 0 then I will not be able to render say, frame 25 with motion blur. This is because if it looks to blur between frame 24 and 25 then I'll have 24 then 25 particles, and it can't blur between a different number.

The solution is to start spawning particles at the life of the particle minus 1, or frame -99 at the latest in this particular example. This way, after frame 0, I consistently have 100 particles in the scene and vray motion blur can handle it. Done!

[Neilg]

Ive been having a problem with motion blur and particle flow recently in that my renders just crash straight away if mblur is turned on, it doesnt even try to render it. Cant even render static frames.

Its geometry driven by particles, there are only 350 or so in the scene. Anyone else had a similar problem?

[stevesideas]

I know this is a fairly old thread, but was this issues ever resolved. I have a scene where the number of particles gradually increases. Im basically simulating material being ejected from a source location. Every time I try and render, I get an unhandled exception error....

Is it not possible to use motion blur with particle flow like this ?

Any responses would be appreciated asap..

Thanks

[vlado]

If you are using instanced particles, make sure you hide the original object that is used as mesh source.

Other than that, motion blur with particle flow should work fine, provided you have enough RAM.

Best regards,
Vlado

[stevesideas]

Im just using shape particles, namely tetra. I have 4 particle systems and they all have their properties set to motion blur - image.

No matter what I do I get the unhandled exception whenever I turn on vray motion blur...

[duke2]

Does this happen regardless of particle count? If it's fixed by reducing the particle count there may be a solution in how PFlow generates the geometry.

[stevesideas]

Basically, the particles are constantly being created from a particular frame. Using an age test I then delete the ones off screen to optimise the solution. So basically the particle count is changing all the time.

Adjusting the actual amount of particles has no effect.

[vlado]

Would be best to get me a scene to vlado@chaosgroup.com then; I have no idea what may be causing this right away.

Best regards,
Vlado