with mantra motion blur is very fast,but i just want to konw,how can i render a motion vector pass out for compsiting! just like nuke's motionUV

i think the velocity is good to use,but if the camera is animate,how can i add the camera motion information?

wish you konw what i said!!

A couple steps involving a few VOPs to your surface shader and a render property on the mantra ROP.

Step 1: Add Get Blur P VOPs
You need to add two Get Blur P VOPs. One with a time input of 0 for shutter start and one with a time input of 1 for shutter end.

Subtract the last from the first and then pass in to a Parameter VOP set to export to an extra image plane (AOV).

Step 2: Modify Output Driver
On the Mantra ROP, add the render property from the parameter Gear menu > Edit Render Parameters… :
“Allow Image Motion Blur” <vm_imageblur>
Disable “Allow Image Motion Blur” as this will disable motion blur in the beauty pass.
Enable the “Allow Motion Blur” toggle.



See the example file. It has a Basic Surface shader with the appropriate vop network in red below the original VOPs.
Since the geometry is deforming as well as translating, I bumped Geo Time Samples to 4 on the Mantra ROP. Notice how the motion vector pass picks that deformation blur up as well as the transform motion blur.

jeff thank you very much, that's what i need