create-2d-physics

# Create and fix Unity 2D physics Do not weigh 3D physics options. If evidence shows the user means 3D, say so and stop. Prefer `WebFetch` over `WebSearch` — faster and lands on the exact reference. Only fetch what you need. Replace `<VERSION>` with the following before fetching: - **docs.unity.com**: The Unity version, e.g. `6000.7`. Pages are markdown — URLs end in `.md`. - **Package on docs.unity3d.com**: The package version, e.g. `@1.1`. Check `Packages/manifest.json` if unsure. ## Important - Use the unity cli (`unity command --format json`) and the `unity-cli` and `unity-pipeline` skills for each step. - Don't use `using` directives or unqualified types in the `snippet` for `eval`. The compiler reads using `UnityEngine` and a bare AssetDatabase, Volume, or Object causes errors (CS0246 / CS0103 / CS0104). `return` what you want to read; it arrives at `data.result.result`. - Create a restore point you can roll back to if your changes fail. - Do only what's asked. Don't change unrelated assets or files. - Avoid long explanations. - Never leave verification code in the user's script; never build logging or settle-detection they didn't ask for. See [Final step](#final-step). - Never reflect over types to discover an API — fetch the member page instead. The system probe is the one exception. ## Step 0: Which physics system Unity has two 2D physics systems. They share no code and never interact. Identify which one before writing any physics code — an answer from the wrong system compiles, runs, and does nothing. Check the request, scene and existing scripts against the table below. Components are the reliable signal — check scene and existing scripts first. Check the user's request wording too: "add a collider" is component language, "spawn a thousand" is script language. | Signal | System | | --- | --- | | Physics Pose, Area, Constraint or Simulation components | Core components, 6000.7+ with the package | | Rigidbody 2D, Collider 2D, Joint 2D, Effector 2D | Legacy | | `Unity.U2D.Physics` or `UnityEngine.LowLevelPhysics2D` types in script | Core in script | | `Rigidbody2D`, `Collider2D`, `Physics2D` types | Legacy | | Both present | Separate simulations. Say so, treat separately | | No signal | Stop and ask, offering the three routes above | Key: - Legacy = Rigidbody 2D and Collider 2D components. - Core components = Physics Pose and Physics Area, requiring `com.unity.2d.physics` and Unity 6000.7+. - Core in script = `Unity.U2D.Physics` API, no package needed. If still unsure which systems are installed, run the probe. If the route is still unknown, stop and ask — offer all three routes and never choose for the user: Probe: ``` unity command eval --caller plugin --skill create-2d-physics --code 'var r = ""; foreach (var n in new[] { "UnityEngine.Rigidbody2D", "Unity.U2D.Physics.PhysicsWorld", "UnityEngine.LowLevelPhysics2D.PhysicsWorld", "Unity.U2D.Physics.PhysicsPose" }) { var f = false; foreach (var a in System.AppDomain.CurrentDomain.GetAssemblies()) if (a.GetType(n) != null) f = true; r += f + ","; } return r;' ``` The Probe returns: legacy present, Core as `Unity.U2D.Physics`, Core as `UnityEngine.LowLevelPhysics2D`, Core components present. Core exists if either Core value is true; the true one gives the namespace. `false` rules that route out. ## System reference Once you know the route, read the matching reference before acting: - [2D Physics Core reference](references/2d-physics-core.md) - components, configuring them, creating bodies in script, ownership, and the full Core topic map. - [Legacy 2D physics reference](references/legacy-2d-physics.md) - the legacy manual topic map. ## Worked examples Prefer in order: the C# example on the type or member page you are using; existing project scripts (match their style); the sample project at `https://github.com/Unity-Technologies/PhysicsExamples2D`. Check all three before inventing a pattern. ## Final step Do the following checks: 1. Check the project has zero console errors. Use `console_status` for counts. 2. Stop there unless the user asked you to prove it works or you suspect a specific fault. 3. If you do enter Play mode, do it once only to chase a fault you already suspect. Read the world through `eval` rather than adding logging. Take no screenshots as they take too much time. If a check fails, go back and reread the docs pages in the matching reference to find out what you missed. ## Final report Short checklist: what you changed and why, which physics system you used, anything left for the user to decide or do.