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MaterialX NPR Shading Nodes

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

Introduction

The MaterialX Standard Nodes 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.

Table of Contents

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, as defined by the shading environment.

The view direction is a normalized vector from the viewer position to the current shading position. In a PBR shading context, it represents the incident direction for primary camera rays, independent of any secondary or reflection rays.

Port Description Type Default Accepted Values
space The space of the view direction vector string world model, object, world
out Output: view direction vector3

NPR Utility Nodes

facingratio

The geometric facing ratio of the view direction and surface normal.

Facing ratio is computed as the dot product between the view direction and surface normal.

Port Description Type Default
viewdirection The input view direction vector vector3 Vworld
normal The input surface normal vector vector3 Nworld
faceforward Makes the output always positive, facing towards the view direction boolean true
invert Inverts the output values by multiplying them by -1 boolean false
out Output: the float representing the ratio between view direction and normal float

NPR Shading Nodes

gooch_shade

Computes the color from single-pass shading portion of the Gooch1 lighting model.

Gooch shade provides an illustrative shading effect by blending colors based on the angle between the surface normal and the light direction. It also provides a simple Phong specular highlight, on top of the warm and cool colors.

Port Description Type Default
warm_color The color facing toward the light color3 0.8, 0.8, 0.7
cool_color The color facing away from the light color3 0.3, 0.3, 0.8
specular_intensity The intensity of the highlight float 1
shininess The size of the highlight float 64
light_direction The world-space direction of the light vector3 1, -0.5, -0.5
out Output: the Gooch lighting model result color3

References

Footnotes

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