Jolt Physics: Bringing Sceneri's Worlds to Life

Jolt Physics is an open-source physics engine that was developed by Jorrit Rouwe, a lead game tech engineer at Guerrilla Games. Jolt Physics is used in a variety of games, including Horizon Forbidden West. It is a multi-core friendly rigid body physics and collision detection library written in C++, suitable for games and VR applications.

History of Jolt

Guerrilla Games, the developer of Horizon Forbidden West, switched from a commercial physics engine to Jolt Physics in order to improve performance and memory usage. Jolt Physics allowed Guerrilla Games to double the simulation frequency of the game while using less CPU time.

In Horizon Forbidden West, Jolt Physics is used to simulate a variety of physical effects, including:

• Collision detection: Jolt Physics uses a quadtree to efficiently detect collisions between objects. This allows for smooth and realistic interactions between the player, enemies, and the environment.
• Rigid body physics: Jolt Physics simulates the movement of rigid bodies, such as the player's character, weapons, and machines. This allows for realistic physics-based interactions, such as the player being knocked back by an explosion or a machine being thrown by a powerful attack.
• Ragdoll physics: Jolt Physics can also simulate the behavior of ragdolls. This allows for realistic and visually appealing death animations for enemies and other characters.

Jolt itself is distributed under an MIT license, which can be found in the following Github repository with additional documentation.

How Sceneri Uses Jolt Physics

Jolt comes deeply integrated to support fully dynamic physics such as walking characters, cars & trucks, and motorcycles. Every scene is dynamic in Sceneri, which is proven further as you can push characters and cars with kinematic components, or attach rope constraints directly to your character to leash them to an area.

Within Sceneri, we utilize Jolt for various setups within the world. As shown below, you can see the standard character on the left hopping toward the end goal. The police vehicle, equipped with a complex axle, drives along the rooftops. Finally, the last character uses a moving platform with friction applied from Jolt to be pushed to the other side of the level.

You can always pause, edit, and resume gameplay, allowing you to supercharge iteration time within the Sceneri Editor. Additionally, Sceneri offers the physics grab tool that can bring dynamics to any object you select within the level when the tool is active.

Advantages of Jolt Physics

• Performance: Jolt Physics is a very efficient physics engine, which means that it can run smoothly even on high-end hardware. This is important for an open-world game like Horizon, which has a large and complex world to explore.
• Scalability: Jolt Physics is also scalable, which means that it can be used to simulate large numbers of objects without sacrificing performance. This is important for Horizon, which has a large number of enemies and other objects in the world.
• Accuracy: Jolt Physics is a very accurate physics engine, which means that the physics simulations are very realistic. This is important for Horizon, which is a game that emphasizes realism.

In summary, Jolt Physics emerges as a robust and versatile physics engine, purpose-built for the demands of open-world games like Horizon. With its efficient, scalable, and realistic capabilities, Jolt Physics has undeniably become an invaluable asset for game developers, enabling them to bring their visions to life and create captivating, physics-driven gaming experiences. For additional information, Jorrit has presented Jolt in a GDC presentation at the following link.

The Sceneri Team