PHYSX 4: RAISING the FIDELITY and PERFORMANCE of PHYSICS SIMULATION in GAMES Kier Storey, Principal Software Engineer | Date | Booth S466| South Hall

PHYSX 4: RAISING THE FIDELITY AND PERFORMANCE OF PHYSICS SIMULATION IN GAMES Kier Storey, Principal Software Engineer | Date | Booth S466| South Hall

www.nvidia.com/GDC PHYSX

Scalable, robust rigid body simulation

Cross-platform

Multi-threaded and GPU accelerated

Visual debugging and profiling tools

Integrated into numerous tools and existing game engines

2 RIGID BODIES

Efficient and accurate distance-based contact generation

Sweep-based CCD and speculative CCD

Support for common joint types (spherical, revolute, fixed, prismatic, distance, custom)

Fast and robust iterative solver

Efficient scene query system

Flexible filtering system

Extensions for vehicles and characters

Two interfaces: “retained” and “immediate” mode

3 PHYSX 4

Open-source BSD license

TGS: New, more robust, non-linear rigid body solver

New reduced coordinate articulation implementation

Provides game-level performance with robotics-quality simulation fidelity

More scalable broad phase

Overhauled joint implementation

Optimizations for complex multi-shape actors

4 TGS SOLVER

Non-linear iterative solver

Improved robustness to ill-conditioned cases

Significantly faster converging than PGS

Improved high-mass ratio simulation

Provides “gentle de-penetration” without damaging convergence

Improved joint drive handling

Similar performance to PGS solver

5 TGS COMPARISON Revolute Chains with Drives

0.3

0.25

0.2

0.15

0.1

0.05

27 53 79

105 131 157 183 209 235 261 287 313 339 365 391 417 443 469 495 521 547 573 599 625 651 677

PGS TGS

6 TGS COMPARISON High-mass Ratio Chains

0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1

179 268 357 446 535 624 713 802 891 980

1069 1158 1247 1336 1425 1514 1603 1692 1781 1870 1959 2048 2137 2226 2315

PGS TGS

7 TGS COMPARISON Toy-scale Kapla tower

20 18 16 14 12 10 8 6 4 2

130 259 388 517 646 775 904

1033 1162 1291 1420 1549 1678 1807 1936 2065 2194 2323 2452 2581 2710 2839 2968 3097 3226 3355 3484

PGS TGS

8 TGS CONVERGENCE 10,000:1 Mass Ratio Chain error 100 iterations

0.5

1.5 Error

2.5

TGS PGS

9 REDUCED COORDINATE ARTICULATIONS

Hierarchical kinematic tree multi-body system

Currently supports fixed, revolute, spherical and prismatic joints

Support for limits, PD drive controllers and joint friction

Loop joints, self-collisions and interactions with external bodies handled through PGS/TGS solver

Inverse dynamics

Closely-matches analytical models

Deep integration with TGS solver yields improved simulation robustness

10 RESULTS PhysX Warehouse Demo

11 RESULTS ANYmal training

12 IMMEDIATE MODE

Direct access to PhysX low-level functionality

Contact generation

Constraint definitions (contacts and joints)

Low-level rigid body solver

Extremely low-overhead. Ideally-suited for simulating small sets of bodies with as little latency as possible.

13 RETAINED MODE IMMEDIATE MODE PxScene* scene = gPhysics->createScene(desc); using namespace physx::immediate; const int nbBodies = 10; scene->addActor(*PxCreatePlane(*gPhysics, PxRigidBodyData bodyDescs[nbBodies]; PxPlane(0,1,0,0), material); PxSolverBodyData data[nbBodies+1]; PxSolverBody solverBodies[nbBodies+1]; PxShape* box = gPhysics->createShape PxConstraintDesc contacts[nbBodies]; (PxBoxGeometry(PxVec3(1.f), material); PxConstructStaticSolverBody( PxRigidDyn* dyn; PxTransformFromPlaneEquation(PxPlane(0,1,0,0)), data[0]); for(int i = 0; i < 1000; ++i) PxConstructSolverBodies(bodyDescs, &data[1], 10); { PxReal dt = 1.f/60.f, invDt = 60.f; dyn = gPhysics->createRigidDynamic (PxTransform(PxVec3(0.f, 1.f+2.f*i, 0.f)); for(int frame = 0; frame < 100; ++frame) dyn->attachShape(*box); { updateMassAndInertia(*dyn, 1.f); applyGravity(&data[1],gravity,nbBodies,dt); scene->addActor(*dyn); int cts = 0; } for(int i = 0; i < nbBodies; ++i){ if(generateContacts(boxGeom, planeGeom, for(int frame = 0; frame < 100; ++ frame) data[i+1],data[0],contacts[cts])) { cts++; scene->simulate(1.f/60.f); scene->fetchResults(true); for(int i = 0; i < cts; ++i) } createConstraints(contacts[i], invDt);

solveConstraints(contacts, solverBodies); integrateSolverBodies(solverBodies); } 14 GPU RIGID BODIES

Hybrid CPU/GPU rigid body simulation

Enabled with flags on the scene

Exact same interface and feature set as CPU simulation

Highly-scalable GPU broad phase

GPU-accelerated distance-based contact generation

GPU-accelerated PGS and TGS solver

Automatically handles transfer of data between host and device

Designed for interactive/gameplay-effecting simulation, not just visual effects

15 PHYSX 4.1 Michelle Lu, Principal Software Engineer | 14 March, 2019 | Booth S466| South Hall

www.nvidia.com/GDC PHYSX 4.1

Extends immediate mode to support articulations and TGS solver

GPU-accelerated articulations (coming soon)

Significantly optimized CPU articulations

Optimizations and bug fixes

17 ARTICULATION SOLVER

Forward dynamics optimizations and fixes

Optimized contact/joint solver solves simple constraints (articulation-rigid) in O(1) time rather than O(logn) time

Improved accuracy of joint drives/limits

Improved convergence

Improved spherical joint support

18 PERFORMANCE IMPROVEMENTS 1000 24 DOF Articulations on the ground

1 6

11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96

101 106 111 116 121 126 131 136 141 146 151 156 161 166 171 176 181 186 191 196 201 206 211 216 221 226 231 236 241 246 251 256 261 266 271 276 281 286 291 296 301 306 311 316 321 326 331 336 341 346 351

PhysX 4.0 PhysX 4.1

19 IMMEDIATE MODE ARTICULATIONS

Small/simple API

Direct access to link/joint properties

Direct simulation functions for forward dynamics on a single articulation

Coupled solver function that solves constraints between articulations and rigid bodies

New snippets showcasing immediate mode articulations and joints

20 IMMEDIATE MODE PERFORMANCE 1 Articulation

0.2

0.18

0.16

0.14

0.12

0.1

0.08

0.06

0.04

0.02

1 4 7

10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97

100 103 106 109 112 115 118 121 124 127 130 133 136 139 142 145 148 151 154 157 160 163 166 169 172 175 178 181 184 187 190 193 196 199

PxScene 4T PxScene 0T Immediate Mode

21 MULTIPLE INDEPENDENT SIMULATIONS 400 simple articulations

22 IMMEDIATE MODE PERFORMANCE 400 Articulations

12 Thousands

1 4 7

10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97

100 103 106 109 112 115 118 121 124 127 130 133 136 139 142 145 148 151 154 157 160 163 166 169 172 175 178 181 184 187 190 193 196 199

PxScene 0T PxScene 4T Immediate Mode Immediate Mode 4T

23 WHEN EVERYTHING INTERACTS! 400 Articulations

50 Thousands

1 4 7

10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97

100 103 106 109 112 115 118 121 124 127 130 133 136 139 142 145 148 151 154 157 160 163 166 169 172 175 178 181 184 187 190 193 196 199

PxScene 4T PxScene 0T Immediate Mode

24 GPU ARTICULATIONS

Work-in-progress

Extends GPU PGS and TGS Rigid Body solver to support articulations

Supports mixed simulation (rigid bodies + articulations)

Provides significant performance uplift compared to CPU-based articulations

Ideally-suited to simulations of 100s or 1000s of articulations and rigid bodies

25 GPU ARTICULATION PERFORMANCE 1800 swinging 18-dof chains with limits

Chart Title 18

10 19 28 37 46 55 64 73 82 91

100 109 118 127 136 145 154 163 172 181 190 199 208 217 226 235 244 253 262 271 280 289 298 307 316 325 334 343 352 361 370 379 388 397 406 415 424 433 442 451 460 469 478 487 496 505 514 523 532 541 550 559 568

PhysX 4.1 CPU PhysX 4.1 GPU

26 GPU ARTICULATIONS Future work

Faithful port of PhysX 4.0 articulation solver completed

Multi-body interaction between articulations and rigid bodies/other articulations complete

GPU version of optimized PhysX 4.1 contact/joint solver currently in the works

Articulation support in GPU TGS solver in progress

27 PHYSX FOR GAMES

PxScene simulation provides a scalable, asynchronous n-body simulation

Ideally-suited for simulating the main gameplay-effecting bodies

Immediate mode ideally suited for smaller-scale physics simulation

Local secondary physics for characters, network replays etc.

GPU simulation can be used to scale simulations massively

e.g. scalable destruction, server-side destruction/simulation etc.

28 NON-GAMING APPLICATIONS

Industrial simulation

Robotics

Reinforcement learning

Immediate mode for low-latency small-scale simulations

GPU articulations for larger-scale simulations

Model-based control

Forward and inverse dynamics

Visual FX

29 BEYOND GAME VEHICLE PHYSICS? Gordon Yeoman, Developer | 14 March, 2019 | Booth S466| South Hall

www.nvidia.com/GDC OUTLINE

PhysX Vehicles are now being used in non-gaming vehicle simulation applications such as NVIDIA DriveSim.

Using games technology in non-gaming applications leads to an obvious question.

Q: What is the integrity of the PhysX vehicle model in scenarios currently of interest?

A: Let’s compare with world class, industry-standard vehicle dynamics simulators and analyse the results.

31 PHYSX VEHICLE FEATURE SET What is a PhysX vehicle?

Engine (1-d rigid body, drive torque curve, damping)

Drivetrain (clutch, gearbox, final drive, differential)

Suspension (spring-damper)

Wheels (1-d rigid body)

Tires (longitudinal/lateral slip angles/forces, non-linear response, friction)

3d rigid body (jointed to sidecars, trailers etc)

32 SIDE BY SIDE COMPARISION I Test methodology

Run PhysX side by side with leading 3rd party simulator used widely by automotive industry

Configure vehicle data to be as closely matched as possible

Run PhysX and leading 3rd party simulator and compare simulation results

Test acceleration, braking, steering conditions that represent usual and safe driving behaviors

33 SIDE BY SIDE COMPARISION II Test methodology

Drive PhysX and 3rd party simulator with identical driving input (steer, brake, throttle) updated at 75Hz

PhysX and 3rd party simulator drive on the same road geometry and friction

Run PhysX and 3rd party simulator at 1KHz

Sample simulation state (wheel rolling speed, vehicle speed) at 60Hz.

Plot trajectory of maneuver

34 THROTTLE AND BRAKE

Rev the engine Engage the clutch Accelerate to top speed in 1st gear Apply the brake at 30 seconds

35 LANE CHANGE MANEUVER

Rev the engine Engage the clutch Throttle forwards Steer maneuver to change lanes (note: placeholder images)

36 QUESTIONS Gordon Yeoman| [email protected]

www.nvidia.com/GDC BEYOND GAME VEHICLE PHYSICS? Gordon Yeoman, Developer | 14 March, 2019 | Booth S466| South Hall

www.nvidia.com/GDC OUTLINE

PhysX Vehicles are now being used in non-gaming vehicle simulation applications such as NVIDIA DriveSim.

Using games technology in non-gaming applications leads to an obvious question:

Q: What is the integrity of the PhysX vehicle model in scenarios currently of interest?

A: Let’s compare with world class, industry-standard vehicle dynamics simulators and analyse the results.

39 PHYSX VEHICLE FEATURE SET What is a PhysX vehicle?

Engine (1-d rigid body, drive torque curve, damping)

Drivetrain (clutch, gearbox, final drive, differential)

Suspension (spring-damper)

Wheels (1-d rigid body)

Tires (longitudinal/lateral slip angles/forces, non-linear response, friction)

3d rigid body (jointed to sidecars, trailers etc)

40 SIDE BY SIDE COMPARISION I Test methodology

Run PhysX side by side with leading 3rd party simulator used widely by automotive industry

Configure vehicle data to be as closely matched as possible

Run PhysX and leading 3rd party simulator and compare simulation results

Test acceleration, braking, steering conditions that represent usual and safe driving behaviors (accelerate, brake, lane change steering)

41 SIDE BY SIDE COMPARISION II Test methodology

Drive PhysX and 3rd party simulator with identical driving input (steer, brake, throttle) updated at 75Hz

PhysX and 3rd party simulator drive on the same road geometry and friction

Run PhysX and 3rd party simulator at 1KHz

Sample simulation state (wheel rolling speed, vehicle speed) at 60Hz.

Plot trajectory of maneuver

42 THROTTLE AND BRAKE

Rev the engine Engage the clutch Accelerate to top speed in 1st gear Apply the brake at 30 seconds

43 LANE CHANGE MANEUVER

Rev the engine Engage the clutch Throttle forwards Lane change maneuver begins at 10s Lane change maneuver ends at 16s

44 QUESTIONS Gordon Yeoman| [email protected]