Augmented mass-spring system for digital hair simulation

Patent metadata

Field	Value
Publication number	US-2026051102-A1
Application number	US-202418808930-A
Country	US
Kind code	A1
Filing date	Aug 19, 2024
Priority date	Aug 19, 2024
Publication date	Feb 19, 2026
Grant date	—

Abstract

In implementations of techniques and systems for digital hair simulation using an augmented mass-spring model, a processing device receives a hair model including multiple hair strands and a head geometry. Each hair strand is discretized into multiple particles connected by multiple first springs. The processing device also defines a rest configuration for each hair strand with ghost positions corresponding to the position of the multiple particles in the rest configuration. Each particle is connected to the rest configuration by second springs. The processing device then simulates the movement of the hair strands in response to an input action using the first and second springs. The simulated movement is presented via a display device.

First claim

What is claimed is:

1 . A method comprising:
receiving, by a processing device, a hair model including multiple hair strands; discretizing, by the processing device, each hair strand of the multiple hair strands into multiple particles connected by first springs; defining, by the processing device, a rest configuration for each hair strand with ghost positions corresponding to an initial position of the multiple particles, each particle of the multiple hair strands being connected to the rest configuration by second springs; simulating, by the processing device using the first springs and the second springs, movement of the multiple hair strands in response to an input action; and presenting the movement of the multiple hair strands via a display device.

2 . The method of claim 1 , wherein the second springs include:
gravity springs connecting each particle of the multiple particles to a corresponding ghost position; and angular springs connecting a particle of a hair strand with a subsequent ghost position, the subsequent ghost position being the corresponding ghost position of a next particle moving from the particle toward a tip of the hair strand.

3 . The method of claim 2 , wherein each gravity spring has an initial length of zero and a tension proportional to a distance between each particle and the corresponding ghost position.

4 . The method of claim 3 , wherein a material stiffness of each hair strand is proportional to an average spring constant for the gravity springs of the hair strand.

5 . The method of claim 4 , wherein a value of a spring constant for the gravity springs of each hair strand linearly deceases as a function of a distance of the particle from a root of the hair strand.

6 . The method of claim of claim 3 , wherein the tension of each gravity spring is set to incorporate non-linear stress-strain curves of hair strands.

7 . The method of claim 2 , wherein each angular spring has a tension proportional to an angle between a first segment and a second segment, the first segment defined by a first line between the particle and the next particle, the second segment defined by a second line between the particle and the corresponding ghost position of the next particle.

8 . The method of claim 1 , wherein the first springs are two-way springs and the second springs are one-way springs.

9 . The method of claim 1 , wherein the input action includes head motion, external forces, grabbing of a subset of the multiple hair strands, trimming of the hair model, or growth of the multiple hair strands.

10 . The method of claim 1 , wherein the multiple first springs include:
edge springs connecting adjacent particles of each hair strand; bending springs connecting particles separated by a single particle along each hair strand; and torsional springs connecting particles separated by two particles along each hair strand.

11 . The method of claim 1 , wherein a quantity of the multiple particles for each hair strand equals a number equal to or between fifteen and twenty particles.

12 . The method of claim 1 , wherein simulating the movement of the multiple hair strands comprises:
initializing a position and velocity of the multiple particles of each hair strand; determining, based on the first springs and the second springs, an updated velocity at multiple time intervals for the multiple particles in response to an external force caused by the input action; and determining, based on the updated velocity, an updated position at the multiple time intervals for the multiple particles of each hair strand.

13 . The method of claim 12 , wherein:
each time interval of the multiple time intervals includes multiple intermediate time intervals; and simulating the movement of the multiple hair strands further comprises for each intermediate time interval comprises:
determining, based on the first springs and the second springs, an intermediate updated velocity at each intermediate time interval for the multiple particles in response to the external force; and
determining, based on the intermediate updated velocity, an intermediate updated position at the intermediate time interval for the multiple particles.

14 . The method of claim 13 , wherein simulating the movement of the multiple hair strands further comprises:
determining, based on inextensibility constraints applied to the updated velocity and the updated position, a first modified velocity and a first modified position of the multiple particles of each hair strand at each time interval; and determining, based on self interactions of the multiple hair strands and collisions with solid objects, a second modified velocity and a second modified position of the multiple particles of each hair strand at each time interval as the updated velocity and the updated position for each time interval.

15 . A computing device comprising:
a processing device; and a computer-readable medium storing instructions that, in response to execution by the processing device, cause the processing device to perform operations including:
receive a hair model including multiple hair strands;
discretize each hair strand of the multiple hair strands into multiple particles connected by first springs, each first spring being a two-way spring;
define a rest configuration for each hair strand with ghost positions corresponding to an initial position of the multiple particles, each particle of the multiple hair strands being connected to the rest configuration by second springs, each second spring being a one-way spring;
simulate, using the first springs and the second springs, movement of the multiple hair strands in response to an input action; and
present the movement of the multiple hair strands via a display device.

16 . The computing device of claim 15 , wherein:
the first springs include edge springs connecting adjacent particles of each hair strand, bending springs connecting particles separated by a single particle along each hair strand, and torsional springs connecting particles separated by two particles along each hair strand; and the second springs include:
gravity springs connecting each particle of the multiple particles to a corresponding ghost position; and
angular springs connecting a particle of a hair strand with a subsequent ghost position, the subsequent ghost position being the corresponding ghost position of a next particle moving from the particle toward a tip of the hair strand.

17 . The computing device of claim 16 , wherein:
each gravity spring has an initial length of zero and a tension proportional to a distance between each particle and the corresponding ghost position; and each angular spring has a tension proportional to an angle between a first segment and a second segment, the first segment defined by a first line between the particle and the next particle, the second segment defined by a second line between the particle and the corresponding ghost position of the next particle.

18 . The computing device of claim 17 , wherein a material stiffness of each hair strand is proportional to an average spring constant for the gravity springs of the hair strand.

19 . The computing device of claim 15 , wherein simulating the movement of the multiple hair strands comprises:
initializing a position and velocity of the multiple particles of each hair strand; determining, based on the first springs and the second springs, an updated velocity at multiple time intervals for the multiple particles in response to

Assignees

• Adobe Inc

Inventors

• Zhou Yi
• Shu Zhixin
• Sun Xin
• Amador Herrera Jorge Alejandro

Classifications

• G06T2210/56

  Particle system, point based geometry or rendering · CPC title

• G06T13/60

  of natural phenomena, e.g. rain, snow, water or plants · CPC title

• G06T13/40 Primary

  of characters, e.g. humans, animals or virtual beings · CPC title