MaterialX NPR Shading Nodes

Version 1.39
Doug Smythe - Industrial Light & Magic
Jonathan Stone - Lucasfilm Advanced Development Group
July 1, 2024

Introduction

The MaterialX Specification and MaterialX Physically Based Shading Nodes documents describe a number of standard pattern and shading nodes that may be used to construct nodegraph-based shaders for physically based rendering in a variety of applications. However, there are certain operations that are desirable in non-photorealistic shading styles but which cannot be implemented within certain rendering constructs. It is also helpful conceptually to separate nodes primarily useful for photorealistic and non-photorealistic shading styles into separate libraries.

This document describes a number of MaterialX nodes primarily applicable to non-photorealistic, or NPR, rendering. Rendering applications whose architecture cannot support these operations are not required to support these nodes.

MaterialX NPR Library
NPR Application Nodes
NPR Utility Nodes
NPR Shading Nodes

References

MaterialX NPR Library

NPR Application Nodes

viewdirection: the current scene view direction (e.g. from the viewing/camera position to the current shading position). If viewdirection is used in a PBR shading context, it should be noted that this would be the same as the incident ray direction for primary ("camera") rays but not for secondary/reflection rays. This node must be of type vector3.
- space (uniform string): the space in which to return the view vector direction, defaults to world.

NPR Utility Nodes

facingratio: returns the geometric facing ratio, computed as the dot product between the view direction and geometric normal. Output is a float between 0.0 and 1.0.
- viewdirection (vector3): the viewing direction, defaults to the value of the "Vworld" (world space view direction) geometric property.
- normal (vector3): the surface normal vector, defaults to the value of the "Nworld" (world space view direction) geometric property. This vector is expected to be prenormalized to length 1.0.
- faceforward (boolean): description needed; default is false.
- invert (boolean): description needed; default is false.

NPR Shading Nodes

gooch_shade: Computes the single-pass shading portion of the Gooch¹ lighting model. Output type surfaceshader.
- warm_color (color3): the "warm" color for shading, defaults to (0.8, 0.8, 0.7) in the lin_rec709 colorspace.
- cool_color (color3): the "cool" color for shading, defaults to (0.3, 0.3, 0.8) in the lin_rec709 colorspace.
- specular_intensity (float): the intensity of the specular component. Defaults to 1.0.
- shininess (float): the specular power typically ranging from 1 to 256, defaults to 64.
- light_direction (vector3): the incoming predominant lighting direction in world space, defaults to (1.0, -0.5, -0.5).

References

Gooch et al., A Non-Photorealistic Lighting Model For Automatic Technical Illustration, https://users.cs.northwestern.edu/~ago820/SIG98/gooch98.pdf, 1998. ↩︎

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