Rendering Displacements

A simple vector displacement test. You can download the Maya scene here and the ear vector displacements map here.
 

displacementNode UI

Scalar Displacements

For scalar displacements, all parameters are recognised but one: Vector Displacement. It is not used for obvious reason: the displacement vector is implicitly the surface normal. Despite the misleading names, both Vector Encoding and Vector Space are supported in the case of scalar displacements.

For scalar displacements, the Vector Displacement parameter is not used.

Vector Space

This parameter, which also applies to scalar displacements, defines in which 3D space the displacement is defined. The available options are:

Vector Encoding

This parameter, which also applies to scalar displacements, defines in which range the displacement is defined.  The available options are:

Vector Displacement Maps

Connecting a texture (or a procedural texture) into the Vector Displacement plug enables vector displacements. In this mode, the Displacement plug is ignored.

Displacement plug is ignored when Vector Displacement is connected.

Here is an example of a network setup to use vector displacement map:

Displacement network to use a vector displacement map (used to render the "ear" scene).

Adjusting the Displacement Bound

As explained in Displacement Technology, 3Delight needs bounds for the displacements to render properly. 3Delight for Maya guesses the correct displacement bound using the parameters in the displacement shader so in most cases the Displacement Bound is better left untouched. In some cases, however, it is necessary to adjust the bound to avoid artifacts or to optimize render times. 

One instance in which the adjustment is necessary is when using floating-point displacement maps (or shading networks) that produce magnitudes larger than 1.0. In this case, the Displacement Bound should be set to the maximum value in the texture map or network. Usually renders which exceed the displacement bound will produce the following 3Delight error :

3DL R2001 object 'name' (displacement 'shader', surface 'shader') exceeded its displacement bound by 25%
A displacement bounds is be specified for the object but is not big enough. This could cut off displaced
parts of the object. Maybe the bounds should be enlarged.

 The following render shows the kind of artifacts produced by insufficient displacement bounds:

Correct Displacement Bounds (left) — Insufficient Displacement Bounds (right)
 

Another instance in which the Displacement Bound should be changed is when the range of the displacement map (or shading network) is much lower than one, in this case the bound should be lowered to reflect the actual range of the displacement map or network. Note this case won't produce artifacts, it is a simple optimization step. When 3Delight detects displacement bounds that are too large, the following warning will be produced:

3DL R2093 object 'name' (displacement 'shader', surface 'shader') used only 25% of its displacement bound
The displacement bound specified for the object is much larger than needed. Performance could be increased by reducing it.

Displacement Technology

3Delight supports two different displacement methods:

1. Pixel level displacement. Geometry is tessellated on-the-fly and adaptively to meet highest quality criteria. This is the default.
2. Vertex level displacement.  Geometry is pre-tessellated to a given amount of subdivision prior to running the displacement shader.  Vertex level displacement is enabled in the displacementNode inside the 3Delight section as show in the screen shot below. 

Enabling Vertex Displacement

Both approaches have their pros and cons as shown in the table below.

Using Mudbox Displacements

3Delight for Maya can render Mudbox displacements (both vector and scalar) using the standard displacementNode shader.  The following table explains how to export both scalar and vector displacement maps.

Disable Smooth UVs.

Using ZBrush Displacement Maps - Docs Work in Progress

In ZBrush you can export displacement maps via:

• Tool →  Displacement
• Tool →  Vector Displacement
• Zplugin → Multi Map Exporter (which allows to export other types of maps in one go).

There are two kind of displacement output:

1. (Scalar) Displacement: this displaces the surface along the normal direction by a scalar value (a single float), either pushing the surface up, or down or both. In scalar displacement the direction cannot vary while displacing the surface. 
2. Vector Displacement: here the surface is displaced through a vector, the encoding allows for multi-directional displacement, so the surface is pushed up/down/both in a direction that may vary while displacing.

In both cases the workflow is the same:

• go the lowest subdivision level of your mesh
• export your displacement map
• export your base mesh model as an OBJ file (or use GoZ).

The relevant sections for displacement maps are evidenced  screenshot:

(Scalar) Displacement and Vector Displacement map  creation options

What Bit Depth to Use ?

This is a very common question and the answer depends on both the type of the map used (scalar or vector) and the type of the displacements used. Disk space consumption can also be a consideration. 3Delight for Maya work fine with all bit depths. The table below provides some hints on what bit depth should be used depending on the situation.