VEX velocity to shake - doing mblur

[Jostein]

OK guys .. mantra is giving me a hard time about mblur .. Is it possible to do a VEX Velocity shader (RGB = XYZ) - and do the mblur 2d in shake?

cheers,

jostein.newbie

[Jason]

The idea is to render the screen-space velocity and use that in Shake or whatever to do your motion blur. Mark Elendt sent in this information a while ago: Od[force] link to velocity goodness.

Good luck,

Jason

[Jostein]

Great!

Thanks a lot!

cheers, jostein.newbie

[David Gary]

Tip for doing this entirely with Houdini (maybe easier...)

1) get the velocity of each point of your SOP.

If your SOP comes from a POP, it already has got a velocity attribute.

If it doesn't, create a new attribute ( with an AttribCreate SOP) and call

it velocity

2) to get the velocity of each SOP point, you need to compute it from it's position.

For this. Use a geometry CHOP, append a Slope CHOP

3) go back in SOPs and append a Channel SOP ( which often works in conjuction with a geometryCHOP) which refers to the Slope CHOP

3) When creating your velocity shader, create a Parameter Vop with parameter name : velocity

and turn on Export Parameter. It will bring the Point Attribute to your shader with interpolating it between each point.

4) You can create a DeepRaster of your object, using a velocity plane.

5) In COPs use a VelocityBlur COP.

See my example ( re-render the scene ). ( done with H6.1.200 NC) Download The Scene Here

Hope it helps.

[AndrewVK]

is "2) + 3)" != "Trail SOP" ????

[David Gary]

is "2) + 3)" != "Trail SOP" ????

Ahem.. Yes!

I usually use the Trail SOP to draw long trails so i didn't think about it.

[Jostein]

I tried to download your file.... but I can't see a thing??

using 6.1.200 apprentice version

jostein.

[anakin78z]

I tried to download your file.... but I can't see a thing??

Hey FrenchOP, try gzip-ing your file before posting. Most browsers screw up unziped files.

[David Gary]

Hi Jostein.

Sorry i didn't answer. I forgot about it because i thought you would only use Shake.

I send you the file again, zipped:

click here:

(But in fact I think my answer is not correct, but we don't see it on a regular object like a plane).

I think you have to convert the velocity attribute to NDC first (just append a ChangeSpaceToNDC vopin the vopnet), because i cannot figure how Houdini can compute the velocity in image space at compositing time, since he lost the information about the camera location (although it is not mentioned in the VelocityBlurCOP help).