motionblur stamped objects to particles

[MisterP]

Hello,

I'm getting some strange motionblur when stamping objects to particles, apologies as this is probably a very stupid question

I'm running a particle sim with a rotation pop and copy stamping rocks to each particle.

Rocks are moving and rotating but are only using a single v vector for the whole rock. I would then enable geometry motionblur at object level and motionblur in the mantra rop, but I get weird motionblur, really strange, I believe because the motionblur does not take into account each rocks own rotation.

I suppose I should replace the inherited v with a new trail sop that takes into account all rock vertices, but the trail wouldn't work in this case as particles would be born and die causing changing number of vertices.

Is the idea of using a v vector correct or am I lookin at this from the wrong angle?

[bandini]

Hello,

I'm getting some strange motionblur when stamping objects to particles, apologies as this is probably a very stupid question

I'm running a particle sim with a rotation pop and copy stamping rocks to each particle.

Rocks are moving and rotating but are only using a single v vector for the whole rock. I would then enable geometry motionblur at object level and motionblur in the mantra rop, but I get weird motionblur, really strange, I believe because the motionblur does not take into account each rocks own rotation.

I suppose I should replace the inherited v with a new trail sop that takes into account all rock vertices, but the trail wouldn't work in this case as particles would be born and die causing changing number of vertices.

Is the idea of using a v vector correct or am I lookin at this from the wrong angle?

You are right that the v attribute won't work for rotations when copy-stamping like you are doing, since all points of the geometry will inherit the same v value, thus no rotational blur, just position blur. Maybe copying the rotation attributes to your geometry and extrapolating a new v attribute might work? Wish I could give you more help here, but I generally just render points and fluids. Haven't done too much with instancing geometry.

[MisterP]

I've prepared a houdini example to illustrate the problem.

Basically if I scatter points, translate them and stamp boxes to them the def motionblur works fine.

If however replace the source points with points coming from a particle system the def motionblur stops working; I'm birthing all particles at once and not killing them, so to keep the point ordering and point num constant.

Any help much appreciated, please take a look at the following example, thanks!

MisterP

broken_motionblur_particles.hip

[anim]

it's caused by the cache node as it caches only at integer frames

so there is no motion between the frames

to correct this

just put $FF instead of $F to Index parm on Cache SOP

and check Blend Position Parameter

(of course particle count should not change)