Q: Houdini Alembic UV's and CarPaintMtl Flake size/scale?

[Rork]

Hi all,

This one is a additional question based on a previous thread:
https://forums.chaosgroup.com/forum/...ated-questions
which was answered quickly and the solution is working great!

But I have another one regarding Alembic UV's & the Carpaint shader.
The Houdini Alembic sim (Vray proxy) has generated UV's along the flow path(s), and I'm trying to use those UV's in for the car paint material flakes.

So far I can get the UV's into the mapping channel with a VRayUser node, but I cannot seem to control the flake size and scale, as in a regular object + uv.
I've tried to remap or rescale the uv's that come with the Alembic, but so far no luck.

We tried various scale outputs in Houdini for the Alembic, but that is not affecting the large flake size in the renders.

Any thoughts & tips will be appreciated

cheers!

rob

[dgruwier]

Maybe a silly question, but have you checked that the uvs are actually working as normal by adding a checker pattern or UV render element or something? Just to check that the UVs haven't been added in a way that vray can't read, even if they appear to be there (happened before to me)

[Rork]

There's no silly questions, especially when it comes to 3d

If I pipe in a checker texture, the checkers follow uv of the flow of the sim nicely.
So it starts to look a a flake issue in the shader, somehow the flakes are generated differently for the uv's?

cheers!

[Rork]

So it seems I have some control by upping the resolution of the sim, the flakes become smaller with the same shader settings.

But it would be nice to be able to have a way of multiplying the values that go into the mapping slot from the VrayUser node, so it is independent of the flake controls.

cheers!

Edit:
converted the 'concrete' material setup from the 'Houdini to Maya Alembic workflow' page to get something working.
Used the float setup to control the UV values on a 2dtexture node. So I can now control the flakes in the shader, and tile them via the FlakeUVCoordinates slot.

[yolov]

Does this mean that you got it working?

[Rork]

Hi,

Yes, sorry if that wasn't clear in my last edit of the last post.

I now split up the red and green channel of the UserColor node into two separate FloatMath nodes and a FloatConstant, that will link to the wrapU and wrapV value of a 2dTexture node.
The 2D Texture pipes into theUvwgen slot of the Carpaint shader. I now can tweak the UV repeats and see my flakes scale accordingly independent of the flake scale/size sliders.

Hope that helps someone too, and if this can be done differently, I'm all ears as well

cheers!

rob

[yolov]

Great, thanks for sharing.