FlowMaps and Rivers

[Psynema]

How exactly do you do the workflow for Flowmaps. I know there's the comb and obstacle nodes in the gameshelf, but if you wanted to copy a fluid simulation, would it be as simple as doing:

0. Timeshift/freezeframe your fluid mesh
1. Attribute transfer the velocity onto your flat river plane from your sculpted fluid sim. 
2. Then with a wrangle, normalize the velocity attribute, then add the X/z values to the UVs? ie @uv += @velocity;

I know people blend the uvs back and forth - one with rest one with the distorted UVs but not sure how to do that - I mean I know how to add the layer node to create a uv2, uv3 etc, but as far as importing into unreal, the extra uv sets created in Houdini don't translate over on my meshes only showing one UV set. 

For Vorticity/foam - I'm assuming you just make a vertex colored mask then blend/lerp to your content?

[mikelyndon]

Hi Gary,

Your setup is pretty much spot on except for step 2.  You can use the flowmap to color node to convert the velocity into a texture space aligned colour map.

I guess you could store the flowmap in the uvs and have multiple uv sets for different states but I think you could get away with a texture to do the same thing.  Houdini should export extra uv sets without any problems.  Make sure they are type float 3 vector and named uv2, uv3, etc and the fbx exporter should pick them up correctly.

And for vorticity/foam it's up to you.  If your mesh has enough resolution you can use vertex colour or you can use another texture (or the spare channel since the flowmap only uses 2) to store the mask.  That's what I did for Gears of War.  Red and Green for the flowmap and Blue for a wind mask.

Mike