fluid velocity render

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I have made a 2d fluid with some simple reactions. I would like to render just the velocity element to be used as a RSMB pass. is there a way for me to put the velocity into the color channel for rendering the fluid? or does mantra have a velocity render pass element that i can attach to a fluid?

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you can rename vel.x, vel.y and vel.z volume primitives to Cd.x, Cd.y and Cd.z

or for more control you can directly access "vel" in any volume shader, transform it to screen space, scale accordingly for RSMB and plug instead of Cd node

[breadbox]

you can rename vel.x, vel.y and vel.z volume primitives to Cd.x, Cd.y and Cd.z

or for more control you can directly access "vel" in any volume shader, transform it to screen space, scale accordingly for RSMB and plug instead of Cd node

ok thanks I will try to do. I think I might need to beef up a bit on my volume rendering because I can really only understand a bit of how to do this. understand the principal, but don't know where the buttons and variables need to go. at first i thought there was a volume sop, similar to point sop, but couldnt find one, so I try to put a point node on the volume, and use $VX,Y,Z to drive the point color, but these are not points so that didnt work out it changed the fluid color, but it did the whole thing, not really blending the result per moving voxel. then i try the same thing in the shop, in the volume shader but that seems to be the place for this control, but i dont know how to make it work with the variables i checked to see what local variable the color imput for the fluid would accept, it seems to not recognize $VX, and i try vel.x too.

FluidVelocity.hipnc

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this is sort of the result I am hoping to achieve. this was rendered in maya with vray, because fluid velocity color is not supported in MR nor VRay, I advected particles in the fluid field and the velocity of the particle does render... now the problem is you can see they are dots and they have some hard edges where if it was a fluid it would render more smooth seamless transitions... the good thing is because its a render element its already set to the range for RSMB plug in... so now to do in houdini

[anim]

no variables, either use name SOP to rename primitives

or Volume VOP SOP to do whatever you want with existing ones

but here is the example how to do it in shader since you need screen space vectors

FluidVelocity_shader.hipnc

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you example is perfect. very interesting. thanks much.