Low-Level Digger

Low-Level Digger is a sample project that demonstrates how to use the new Low-Level 2D Physics feature in Unity 6.3.

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System Requirements

• Unity 6.3

What Is Low-Level 2D Physics?

Low-Level 2D Physics is a new feature in Unity 6.3 that allows you to access the 2D physics engine (Box2D v3) through a very thin C# wrapper. This design makes it possible to handle large numbers of physics objects efficiently, without the overhead typically introduced by the GameObject- and Component-based abstraction layers.

In this project, for example, the system simulates 1,024 rigid bodies representing small dirt particles inside the bucket. In the Editor and Standalone Players, the simulation runs across multiple worker threads, keeping CPU usage low. Even in Web builds (WebGL/WebGPU), where execution is limited to a single main thread, the simulation remains performant enough to run smoothly.

Where Should I Start?

Unity provides an official sandbox sample project that showcases the Low-Level 2D Physics features in a comprehensive way. It is highly recommended to try this project first to understand what is available and to get a sense of the performance characteristics.

As a next step, you may consider using AI coding agents with proper guidance. As described in the AGENTS.md file of this repository, you should instruct them to refer to the latest Unity documentation and the official sample project above.

It is also recommended to explicitly mention Box2D v3 in the system prompt for AI agents (as defined in AGENTS.md). While they may not have specific knowledge about Unity’s Low-Level 2D Physics API, they generally have a solid understanding of Box2D itself, and that knowledge transfers well because the wrapper layer in Unity is very thin.

For further documentation, samples, and community-provided insights, see the official Unity Discussions thread.

Brief Project Structure

There are two main categories of physics objects in this project:

• Dirt particles managed by DirtManager — The small dirt particles are handled by a single component called DirtManager. These particles (which are physics bodies internally) are generated, pooled, and recycled by this component. Rendering is handled by a dedicated DirtRenderer, which uses a specialized vertex shader to apply per-particle transforms to a shared mesh, allowing all particles to be drawn in a single draw call.

• Physics bodies synchronized with GameObjects — Other physics bodies, such as the bucket, gems, scoop, and tray, are handled by two bridge components: DynamicBodyBridge and StaticBodyBridge. These components create and manage physics bodies while synchronizing their transforms with GameObjects. This approach allows the key interactive elements of the game to be authored and controlled using the conventional GameObject-based workflow. In addition, the CompositeShapeBuilder component provides an editor-friendly way to author composite collision shapes.

Generative AI Usage Disclosure

Some assets and code in this project were created with the assistance of generative AI tools.

• Sprite assets (located in the Assets/Sprites folder) were generated using the Gemini image generation feature (Nano Banana).
• Source code was developed and finalized by the author; however, OpenAI Codex CLI was used during the development process for code generation, refactoring suggestions, and exploratory prototyping. All generated outputs were reviewed, modified, and integrated manually.