Hi

I have a very simple dops scene, but for reason i can't get it to render with motion blur. I'm sure i'm missing a check box somewhere!

Any help would be great.

Thanks

Hiya, before I address the specific problem, I figure a brief rundown of motion blur in Houdini couldn't hurt, as it's a pretty common problem:

With motion blur you generally have two options, deformation blur and velocity blur.

Deformation blur is the deafult, and it uses the subframes of your animation - so you won't be able to use it if your subframes aren't being calculated correctly, which is generally a problem if you have changing point counts. The best way to check subframes is to uncheck “Integer Frame Values” in the Global Animation Options (right of the timeline). If your point counts aren't changing, but you don't have subframes, you can create them with a TimeBlend SOP.

None of this is relevant to your problem however! The reason being that you've enabled “Geometry Velocity Blur” at the object level (under Render -> Sampling). Velocity blur doesn't use subframes, but instead relies on a velocity attribute on your geometry, which you don't have. Because this is being calculated in your dopnet, you can pull it in by using a DOP Import SOP instead of the Object Merge you're using. That way, you get the velocity attribute, and velocity motion blur will work. Alternative, you can Compute Velocity with a Trail SOP, but this has the same caveat as deformation blur, and needs consistent point counts.

Your point counts aren't changing in a simple scene like this, so either option works. Where possible you want to use deformation blur, as it's more accurate than velocity blur.

tl;dr: Uncheck “Geometry Velocity Blur” on your fetch_ball object.

Hope that helps.

Thanks, i have motion blur! I guessed it was something to do with the motion from dops.

Really apprechiate the time to write a detailed expalination.

Thanks again.