Vector Displacement from Mudbox to Arnold

 

In this tutorial, we will take you through the process of rendering a head model from nothing but a sphere and a vector displacement map. Vector displacement maps are a powerful and efficient way to add detail to your scene without the overhead of managing complex geometry. They provide a very efficient workflow when working with models from 3D sculpting applications and Arnold. Unlike traditional gray scale displacement maps which simply use a line long for the vertex normal, vector displacement maps have RGB values which represent the XYZ displacement direction and size. This means they don't follow a fixed surface normal and can move in any direction, including overlapping each other.

However, vector displacement maps have larger file sizes because they have to store more information than regular displacement maps. Also bear in mind that vector displacement maps, as with normal displacement maps, are not perfect for every situation. For example, UV seams can be problematic when using vector displacement maps.

Many thanks to the very talented Zeno Pelgrims for providing the assets and assistance for this tutorial.

The sphere.obj, vector displacement map and diffuse color map can be downloaded here.

Ensure that you enable Texture Coords when importing the sphere.obj file (off by default) otherwise, the UVs will be missing and you will get incorrect displacement.

Mudbox

The original head sculpt has been extracted from Mudbox using the following settings.

Mudbox sculpt details

 

  • The vector displacement was extracted from the original head model in Mudbox under the menu UVs & Maps> Extract Texture Maps> New Operation

 

  • Mudbox provides the following settings for extracting textures from models. In this case, we chose Vector Displacement Map and changed the Vector Displacement to Absolute Tangent. Ensure that the map is saved using 32-bit FP depth and has a high enough resolution. This will give us an accurately displaced render in Arnold.

Make sure that you use a 32bit or 16bit floating-point format to store your image, and not an integer format. An integer format will not work correctly. This is because integer formats do not support negative pixel values, which are used by floating-point displacement maps.

Maya

  • Open the model - sphere.obj. You should see the original subdivided cube called obj_base.

obj_base

 

Vector Displacement Shader

  • Assign a Standard Surface shader to the sphere model. Create an image file texture and open the file Diffuse_colour.jpg. Connect it to the Base Color and the SSS Color attributes. Increase the SSS Weight to around 0.5.
  • Create a Displacement shader and connect it to the Displacement mat. attribute of the Standard shader's shading group.
  • Create an image file texture and open the vector displacement map - mudbox_vdisp.tifConnect it to the Vector Displacement attribute of the displacement shader as in the image below. Increase the Scale to and ensure that the Vector Space is set to Tangent.

Vector Space is set to Tangent

 

  • The final shading network should look like the following image.

 

Subdivisions

  • Ensure that you have enough subdivisions for the sphere geometry otherwise, the displacement will not look correct. In this case, 6 iterations with Type set to Catclark is sufficient.

 

You can see a subtle difference in quality between 4 and 6 subdivision iterations in the images below.

 

The Utility shader can be useful for diagnosing issues when rendering displacement maps.

Utility shader. Shade mode set to ndoteye and Overlay Mode set to polywire.

 

That concludes this tutorial on rendering vector displacements from Mudbox with MtoA.

 

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