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Phase-Functioned Neural Networks for Character Control
A phase-conditioned network that generates real-time locomotion, the breakthrough for neural character controllers.
Abstract
This paper presents the Phase-Functioned Neural Network (PFNN), a real-time character control architecture in which the network weights are generated each frame by a cyclic phase function, implemented as a cubic Catmull-Rom spline parameterized by the phase of the motion cycle. The network takes user controls, the previous character state, and the surrounding terrain geometry as input and produces high quality locomotion that adapts to rough terrain, obstacles, and low ceilings through walking, running, jumping, climbing, and crouching. To train the system, motion capture data is fitted to a large database of heightmaps extracted from virtual environments. By explicitly handling the phase, the PFNN avoids the dying-out and blending artifacts of autoregressive RNN models while remaining compact and fast, requiring only milliseconds of execution and a few megabytes of memory even when trained on gigabytes of data.
How to read this
- Category
- Method: a neural network architecture for real-time character control
- Contributions
- The Phase-Functioned Neural Network, whose weights are regenerated each frame by a cyclic phase function (a cubic Catmull-Rom spline over the motion-cycle phase)
- Real-time, terrain-adaptive locomotion (walking, running, jumping, climbing, crouching) from user controls, prior state, and surrounding terrain geometry
- A compact, fast model that avoids autoregressive RNN dying-out and blending artifacts while training on motion fitted to large heightmap databases
- Context
- Bridges data-driven control approaches such as Clavet's Motion Matching and the deep-learning motion synthesis line (Holden et al.), introducing explicit phase conditioning for character controllers.Builds on: Motion Matching and The Road to Next-Gen Animation · A Deep Learning Framework for Character Motion Synthesis and Editing
- Correctness
- Demonstrated on locomotion with explicit cyclic phase; readers should remember the phase assumption suits cyclic motion well, that preparing training data requires fitting captures to terrain heightmaps, and that non-cyclic actions are a less natural fit for this parameterization.
- Clarity
- Well written and influential; a first pass conveys the phase-function idea clearly, a second pass covers the data preparation and network details.
- How to read it
- Focus on the phase-function weight-generation idea and why it beats autoregressive blending; a second pass on data fitting and the spline parameterization pays off given how foundational this work is.
Builds on
Built upon by
- Character Control with Neural Networks and Machine Learning 2018
- Mode-Adaptive Neural Networks for Quadruped Motion Control 2018
- Character Controllers Using Motion VAEs 2020
- Learned Motion Matching 2020
- MoGlow: Probabilistic and Controllable Motion Synthesis Using Normalising Flows 2020
- Machine Learning Summit: Full-Body Animation Generation for Expressive NPCs 2021
- MotionBricks: Scalable Real-Time Motions with Modular Latent Generative Model and Smart Primitives 2026
Related work
- A Deep Learning Framework for Character Motion Synthesis and Editing 2016 / SIGGRAPH
- Neural State Machine for Character-Scene Interactions 2019 / SIGGRAPH Asia
- DeepPhase: Periodic Autoencoders for Learning Motion Phase Manifolds 2022 / SIGGRAPH
- Learned Motion Matching 2020 / SIGGRAPH
Keywords
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