Hi,

I'm trying to render out velocity vectors from a pyro simulation. My intention is to use this to morph subframes to a realtime particle flip-book animation.

I have tried to use Blur P node in the Volume Shader but this doesn't seem to get me anything but the render images coordinates.

I have exported a vel and this returns 3d vectors but I need to get rid of the fade out in the edges.

I think that Blur P method would be prefered since it is a vector in 2d image space so I really want that to work.
Is this possible or are there any another ways? Any hints?

to get screen space velocity you want something along the lines of:

v = toNDC(getblurP(1))*res - toNDC(getblurP(0))*res;

To prevent opacity compositing, export the image plane on the rop with sample filter “closest surface” and pixel filter “minmax omedian” You may need to disable stochastic sampling to get a usable result, however.

Thanks jsmack,

I still don't get anything useful from the blurP… only unmodified 2d camera space texture coordinates.
The pixel filter seemed to work. Maybe it would be possible to add screenspace UV coordinates to the smoke… Will investigate that…

Can someone confirm that it is vel that is used for BlurP? Or am I barking att the wrong tree? Do I need another position attribute like rest or something?