How to set up vector bump?

[Teemu_Valkama]

Hi!

I'm trying to set up an ocean scene with vector displacement maps rendered from houdini in 32bit exr.

Displacement seems to work fine, but I'm having trouble adding any sort of adjustable bump mapping on top of the displacement, to achieve small detail without blowing up rendertimes due to increased subdivision needs.

I've tried with the arnold c4d ocean tutorial displacement exr with the same results. I've tried plugging the exr to the normal of a standard surface in these ways:

- using both 'image' and the c4d 'image' node (I have to use latter, as it's an image sequence)
- plugging straight
- plugging through a normal map node (tested all the options, including from the advanced menu)
- plugging through a bump2d node

In a small test scene, I do get bump if I use the "Auto bump" option in the arnold tag displacement options, but..
- it will bug out in a large scale ocean geometry for some reason, resulting in a grid pattern
- I would like to have total control of the bump amount
- I can't transition from displacement to pure bump mapping (far away) with this method

I'm using C4DtoA 2.2.4, Arnold core 5.0.2.4, C4D Studio R19.053

Any ideas?

Thanks in advance.

Here's a preview with a "auto bump" on the left, and normal map image -> normal map node -> standard surface normals on the right:

Edit:
Here's the grid problem with auto bump. In the arnold tag I've tried with linear/catclark subdivs, smooth tangents and ignore frustrum culling. I put in a bit of the wireframe to the right side of the image. The grid bug does not correspond to the subdivided, nor to the original geometry, which has a larger grid than in the bug.

[lee_griggs]

I'm a bit confused. Are you using the vector displacement as a normal map? It should be connected to the Arnold Displacement port as per here.

A fractal -> bump should give you some extra detail on top of that.

If that does not work can you post your scene?

[Teemu_Valkama]

Hi Lee!

You're absolutely correct. I'm trying to use vector displacement as a normal map. Should work, as I can get results with the "auto bump" option. But, as that is not adjustable and seems buggy, I'm trying to find another way of plugging the vector displacement map to the normal of the shader.

I will use some other noise map for the small details, as you suggested, if I can't make this work otherwise.

I attached the test scene for the first image: vector-bump.zip. You need the arnold help ocean vector displacement exr with it from here, as the upload size limit was 2mb.

[lee_griggs]

ok, I see from your scene that you are missing the Vector Displacement shader.

>But, as that is not adjustable and seems buggy,

Buggy in what way?

[Teemu_Valkama]

So, I guess you are saying that the only way to get "bumpy" effect from a vector displacement map, is to drive it through the vector displacement shader and then use the "auto bump" feature of the arnold tag. That's a shame if it so, and very surprising. If arnold can generate "auto bump" on top of a practically zero displaced and unsubdivided surface, it should imo be able to do that without the vector displacement shader altogether. Might be wrong there.

You can see the bugginess in the second image in my original post. There's a grid like effect on top of the ocean when using auto bump.

[lee_griggs]

The ocean scene is available here , btw.