Havok Physics Particles Technical Overview (SDK)

Havok Physics Particles are lightweight rigid bodies that simulate and interact with the game with a low performance cost, allowing developers to create large numbers of small solid objects with similar properties to create various game effects. This feature provides lightweight physics simulation at a fraction of the cost of gameplay-critical rigid bodies and aims to offer high performance simulation, with some limitations on quality, while keeping visual artifacts to a minimum. 

The Physics Particles that exist in the Havok Physics SDK are not a full particle system pipeline, but a technology focused on collision detection for particles that are managed by a user system and are made to be easily integrated into existing particle systems.  

There are two main categories of Physics Particle based on the degree of freedom (DOF) the body has. Both categories are for solid objects and are intended for different scenarios.  

(movement along x, y, z axes, yaw, pitch and roll)

6DOF particles are used to create solid objects in the game, specifically intended for non-gameplay-critical convex objects. Since Physics Particles focus on performance and visual quality, they are most suitable for elements related to gameplay experience, amplifying environmental effects, and enhancing game feel.

Such as: debris from explosions, crashes or destruction, decorative pieces, ornaments, bottles, trash cans, garbage, fallen leaves, bullet casings

(movement along x, y, z axes)

3DOF particles are used to create large numbers of point or sphere particles that can be used to create special effects and more interactive environments.

Such as: sparks, smoke, fire, mist, rain, snow fall, fog, swarms of small animals or insects.

These are only general guidelines for the use of Havok Physics Particles, and different combinations and extensions can be used to create unique behavior based on different use case requirements. For instance, Havok Physics Particles can be used to create rudimentary fluid simulation, and viscous bodies like goo.

When created Physics Particles are stored in a buffer (an array for a static number of particles, or a chunked array if the number of particles will change) and are assigned some basic properties:

Particle Shape

Each particle can be assigned its own shape, or all particles can use the same shape. It is important to note that increased complexity in particle shapes and sizes will increase the memory used.

Particle Collisions

Particles can be set to collide with each other or to ignore other particles when reacting to collisions. All collisions between particles use a simple sphere collider for increased performance.

Rigid Body Collisions

Particles can either ignore or collide with dynamic rigid bodies and/or static rigid bodies depending on your requirements. All collisions between particles and rigid bodies do a full collision calculation (unlike the simplified particle-particle collisions) to make sure particles can accurately interact with the gameplay critical world.

Materials

Particles are assigned friction and restitution values to modify their interactions and behaviour.

Above all, Havok Physics Particles allow you to add more light weight rigid body simulation to your game without increasing the memory usage. Letting you achieve more with the same simulation budget.

When taking a scene with 10,000 rigid bodies, and replacing them with Havok Physics Particles, you will see a performance benefit that typically varies between a factor 4 and 6 depending on the simulation.

Beyond the number of particles in a scene, the performance is also influenced by the movement of particles, particle shapes and the kinds of collisions that are enabled.

For instance, enabling angular effect (6DOF) on a basic sphere particle will not only change the behavior of the particle, but it also adds roughly 15% to simulation cost.

Table of collision types and values

Like all features in the Havok Physics SDK, Physics Particles are cross platform deterministic by default. This means that the behavior and performance of the particles will be the same on every supported platform.

Physics Particles, can however, be made non-deterministic if you require a different number of particles to show depending on the processing power of the platform This application of Physics Particles isn’t entirely out-of-the-box so we’re recommend discussing it with your Havok account manager first.

Havok Physics Particles are already used in several released games and are continuously being improved to cater to the needs of games in development and future requirements.

Havok 2025.1 included a significant refactor of the Physics Particles including new features and performance improvements, and further updates are planned for Havok 2025.2.

To find out more about Havok Physics Particles, see the following resources:

Play the free Havok Balloons Tech Showcase available on Steam

GDC Vault – Visual Effects Summit: Redefining Physical VFX Systems  (GDC Vault access required)

GDC Vault – Advanced Physics in ‘ASTRO BOT’ (GDC Vault access required)