Unity3D 进阶教程 - 19 高级物理与自定义碰撞

概述

入门系列第 07-08 篇介绍了 PhysX 引擎的基础——Rigidbody、Collider、碰撞事件。当游戏需要 非标准碰撞形状、自定义物理材质、大规模碰撞检测、或 超越 PhysX 的功能 时，内置物理引擎就不够了。

本篇覆盖：物理查询高级用法、CCD（连续碰撞检测）、Physics Scene、以及用 Job System 实现自定义物理。

1. 物理查询进阶

1.1 批量查询

public class AdvancedPhysicsQuery : MonoBehaviour
{
    private readonly RaycastHit[] _results = new RaycastHit[32];
    private readonly Collider[] _overlapResults = new Collider[32];

    private int BatchRaycast(Vector3 origin, Vector3 direction, float distance)
    {
        return Physics.RaycastNonAlloc(origin, direction, _results, distance);
    }

    private int OverlapSphere(Vector3 center, float radius)
    {
        var layerMask = LayerMask.GetMask("Enemy", "Obstacle");
        return Physics.OverlapSphereNonAlloc(center, radius, _overlapResults, layerMask);
    }
}

1.2 使用 LayerMask 过滤

public class LayerMaskFilter : MonoBehaviour
{
    public void FilteredQuery()
    {
        var playerMask = LayerMask.GetMask("Player");
        var playerAndEnemy = LayerMask.GetMask("Player", "Enemy");

        Physics.Raycast(transform.position, transform.forward, out var hit, 100f, playerAndEnemy);
    }
}

---

2. CCD（连续碰撞检测）

默认 PhysX 使用离散碰撞检测——物体移动过快时会穿透薄物体。CCD 解决这个问题：

public class CCDSetup : MonoBehaviour
{
    private void Start()
    {
        var rb = GetComponent<Rigidbody>();

        rb.collisionDetectionMode = CollisionDetectionMode.ContinuousDynamic;
    }
}

CCD 模式	性能开销	防穿透效果
Discrete	最低	高速穿透
Continuous	中等	对静态物体有效
Continuous Dynamic	最高	所有物体

---

3. 自定义物理场景

3.1 独立物理场景

public class CustomPhysicsScene : MonoBehaviour
{
    private PhysicsScene _physicsScene;

    private void Start()
    {
        var parameters = new CreateSceneParameters(LocalPhysicsMode.Physics3D);
        var scene = SceneManager.CreateScene("PhysicsScene", parameters);
        _physicsScene = scene.GetPhysicsScene();
    }

    private void FixedUpdate()
    {
        if (_physicsScene.IsValid())
            _physicsScene.Simulate(Time.fixedDeltaTime);
    }
}

3.2 手动控制模拟

public class ManualPhysics : MonoBehaviour
{
    private void Start()
    {
        Physics.autoSimulation = false;
    }

    private void Update()
    {
        Physics.Simulate(Time.fixedDeltaTime);
    }
}

---

4. Job System 自定义物理

当 Unity 物理引擎成为瓶颈时，用 Job System 实现轻量级自定义物理：

[BurstCompile]
public struct CustomPhysicsJob : IJobParallelFor
{
    public NativeArray<float3> positions;
    public NativeArray<float3> velocities;
    public NativeArray<float> radii;
    public float deltaTime;
    public float3 gravity;

    public void Execute(int index)
    {
        velocities[index] += gravity * deltaTime;
        positions[index] += velocities[index] * deltaTime;

        // 地面碰撞
        if (positions[index].y < 0)
        {
            positions[index].y = 0;
            velocities[index].y = -velocities[index].y * 0.5f;
        }
    }
}

4.1 球体碰撞

[BurstCompile]
public struct SphereCollisionJob : IJobParallelFor
{
    public NativeArray<float3> positions;
    public NativeArray<float3> velocities;
    [ReadOnly] public NativeArray<float> radii;

    public void Execute(int index)
    {
        var pos = positions[index];
        var vel = velocities[index];
        var rad = radii[index];

        for (int j = index + 1; j < positions.Length; j++)
        {
            var delta = positions[j] - pos;
            var dist = math.length(delta);

            if (dist < rad + radii[j])
            {
                var normal = delta / dist;
                var overlap = (rad + radii[j]) - dist;

                positions[index] -= normal * overlap * 0.5f;
                positions[j] += normal * overlap * 0.5f;

                var relVel = velocities[j] - vel;
                var velAlongNormal = math.dot(relVel, normal);
                if (velAlongNormal > 0) continue;

                var impulse = normal * velAlongNormal;
                velocities[index] += impulse;
                velocities[j] -= impulse;
            }
        }
    }
}

---

5. 物理稳定性提升

public class PhysicsStability : MonoBehaviour
{
    private void Awake()
    {
        Physics.defaultSolverIterations = 10;
        Physics.defaultSolverVelocityIterations = 4;
        Physics.defaultMaxAngularSpeed = 50f;
        Physics.defaultContactOffset = 0.01f;
    }
}

---

总结

• 物理查询：批量 NonAlloc 版本避免 GC，LayerMask 精确过滤
• CCD：高速物体开启 Continuous 防穿透
• 自定义物理场景：隔离物理计算
• Job System 物理：简单碰撞可以完全绕过 PhysX 自己实现
• 空间分区：Grid / QuadTree / Octree 减少 O(n^2) 碰撞对

下一篇是最后一篇 完整项目框架搭建，综合运用本系列所有知识构建可扩展的游戏架构。