How Destructible Meshes Break Apart in Games

In modern game development, creating realistic destruction relies on advanced physics systems that calculate how and when a 3D model should break. This article explores the mechanics behind destructible mesh fragment systems, detailing how physics engines calculate impact stress, determine fracture points using Voronoi diagrams, and simulate realistic debris propagation during real-time gameplay.

Pre-Fracturing and the Voronoi Diagram

To maintain high performance, game engines rarely slice 3D meshes in real-time. Instead, developers use a process called pre-fracturing. Before the game runs, a solid mesh is divided into smaller chunks, often using a mathematical algorithm called Voronoi tessellation.

This algorithm distributes point sites across the mesh and divides the volume into cells based on the closest distance to these points. The resulting fragments are grouped together to look like a single, seamless object. A hidden “support graph” or “connectivity graph” is then generated, mapping which fragments are physically touching and bonded to one another.

Calculating Impact Stress

When an object—such as a projectile or a vehicle—collides with a destructible mesh, the physics engine calculates the force of the impact. The system looks at several key variables:

Using these variables, the engine calculates the stress applied to the mesh’s support graph. Stress is defined as force applied over an area. If the calculated stress at the impact point exceeds the pre-defined “damage threshold” or “yield strength” of the material (e.g., glass has a low threshold, while reinforced concrete has a high threshold), the system initiates the destruction sequence.

Damage Propagation and Bond Breaking

Once the impact stress exceeds the threshold, the physics engine propagates the remaining energy through the connectivity graph.

  1. Local Damage: The fragments directly at the impact point have their bonds immediately severed.
  2. Stress Propagation: The energy travels outward to adjacent fragments. The engine calculates how much force is lost as it travels through the material (damping).
  3. Bond Severing: If the propagated force at any connected edge in the graph exceeds the bond strength between those two fragments, that bond is broken.

If an entire cluster of fragments loses all of its connections to the “anchored” parts of the mesh (the parts connected to the ground or static environment), that cluster becomes physically detached.

Transitioning to Active Rigid Bodies

To save CPU and GPU resources, destructible fragments start in a “kinematic” or sleep state, meaning they do not calculate individual physics. They behave as a single static object.

The moment the bonds in the connectivity graph are broken, the affected fragments instantly transition into “dynamic” rigid bodies. The engine assigns physical properties to each freed chunk: * Mass and Center of Mass: Calculated based on the volume of the individual fragment. * Velocity: The residual kinetic energy from the impact is transferred to the fragments, pushing them outward. * Gravity and Collision: The active fragments fall, collide with the environment, roll, and bounce using standard rigid-body physics.

By combining pre-fractured geometry, graph-based stress propagation, and dynamic state switching, game engines can simulate highly complex, realistic structural collapse without stalling the game’s frame rate.