unity-physicscore2d-factories

name	unity-physicscore2d-factories
description	Factory patterns for creating complex physics objects (ragdolls, soft bodies, vehicles, gears, mechanical systems)

Unity PhysicsCore2D Factories Expert

You are now acting as a Unity PhysicsCore2D factories expert, specialized in creating complex physics objects using factory patterns.

Overview

Factory patterns help create complex multi-body physics systems:

• Ragdolls - Articulated character physics
• Soft bodies - Deformable objects
• Vehicles - Cars, bikes, and wheeled systems
• Gears - Mechanical components
• Mechanical systems - Complex interconnected objects
• Doohickeys - Miscellaneous composite objects

Repository Examples

Reference factory implementations from the PhysicsExamples2D repository:

• RagdollFactory.cs - https://github.com/Unity-Technologies/PhysicsExamples2D/blob/master/Sandbox/Assets/Scripts/RagdollFactory.cs
• SoftbodyFactory.cs - https://github.com/Unity-Technologies/PhysicsExamples2D/blob/master/Sandbox/Assets/Scripts/SoftbodyFactory.cs
• CarFactory.cs - https://github.com/Unity-Technologies/PhysicsExamples2D/blob/master/Sandbox/Assets/Scripts/CarFactory.cs
• GearFactory.cs - https://github.com/Unity-Technologies/PhysicsExamples2D/blob/master/Sandbox/Assets/Scripts/GearFactory.cs
• DoohickeyFactory.cs - https://github.com/Unity-Technologies/PhysicsExamples2D/blob/master/Sandbox/Assets/Scripts/DoohickeyFactory.cs
• GearComponent.cs - https://github.com/Unity-Technologies/PhysicsExamples2D/blob/master/Sandbox/Assets/Scripts/GearComponent.cs

Factory Pattern Benefits

Code Organization

• Encapsulate complex creation logic
• Reusable object templates
• Centralized configuration
• Easier maintenance

Consistency

• Standardized object creation
• Shared definitions and properties
• Predictable behavior
• Version control

Performance

• Batch creation opportunities
• Shared geometry reuse
• Optimized initialization
• Memory pooling

Ragdoll Factory

Ragdoll Structure

Multi-body articulated character:

• Head body
• Torso bodies (upper/lower)
• Arm bodies (upper/lower/hand)
• Leg bodies (upper/lower/foot)
• Joints connecting body parts

Ragdoll Creation Process

1. Define body part dimensions
2. Create PhysicsBody for each part
3. Add shapes to each body
4. Create joints between connected parts
5. Configure joint limits
6. Set collision filtering

Ragdoll Considerations

• Mass distribution affects stability
• Joint limits for realistic motion
• Collision filtering to prevent self-collision
• Motor drives for active ragdolls
• Balance between stability and flexibility

Soft Body Factory

Soft Body Composition

Deformable objects using particles and joints:

• Grid or blob of connected bodies
• Distance joints maintain structure
• Pressure simulation (optional)
• Surface shapes for collision

Soft Body Types

• Pressure-based - Inflated objects
• Grid-based - Cloth and deformables
• Blob-based - Jelly-like objects
• Spring mesh - Flexible structures

Creation Steps

1. Generate particle positions
2. Create bodies for particles
3. Connect neighbors with joints
4. Add surface collision shapes
5. Configure joint stiffness
6. Set particle masses

Tuning Parameters

• Stiffness: joint frequency
• Damping: joint damping ratio
• Particle mass and density
• Pressure (for inflated bodies)
• Surface shape properties

Vehicle Factory

Vehicle Components

Car or wheeled vehicle:

• Chassis body (main body)
• Wheel bodies (4+ wheels)
• Wheel joints (suspension)
• Motor drives for propulsion
• Steering mechanism

Vehicle Creation

1. Create chassis body with shape
2. Create wheel bodies
3. Attach wheels with wheel joints
4. Configure suspension (joint springs)
5. Add motor drives to powered wheels
6. Setup steering control

Vehicle Tuning

• Suspension stiffness and damping
• Wheel friction and mass
• Motor torque and speed
• Chassis center of mass
• Anti-roll bars (optional)

Gear Factory

Gear Systems

Rotating mechanical parts:

• Gear bodies with teeth
• Hinge joints at centers
• Tooth collision or gear ratios
• Rotation constraints
• Motor drives

Gear Connections

• Meshed gears - Touching, opposite rotation
• Gear ratios - Size determines speed ratio
• Gear trains - Multiple connected gears
• Planetary gears - Advanced configurations

Implementation Options

1. Physics-based - Actual tooth collision
2. Constraint-based - Joint with gear ratio
3. Hybrid - Constraints with visual teeth

Doohickey Factory

Miscellaneous Mechanisms

Complex composite objects:

• Multiple interacting parts
• Various joint types
• Mixed static and dynamic bodies
• Triggers and sensors
• Custom behaviors

Examples

• Rube Goldberg machines
• Catapults and trebuchets
• Contraptions and gadgets
• Mechanical puzzles
• Interactive props

Factory Implementation Pattern

Basic Factory Structure

public class MyObjectFactory
{
    // Configuration
    public float size = 1.0f;
    public PhysicsMask collisionMask;

    // Create method
    public void Create(PhysicsWorld world, Vector2 position)
    {
        // 1. Create bodies
        var bodies = CreateBodies(world, position);

        // 2. Add shapes
        AddShapes(bodies);

        // 3. Create joints
        CreateJoints(bodies);

        // 4. Configure properties
        ConfigureProperties(bodies);
    }

    // Helper methods
    private NativeArray<PhysicsBody> CreateBodies(PhysicsWorld world, Vector2 position)
    {
        // Body creation logic
    }

    private void AddShapes(NativeArray<PhysicsBody> bodies)
    {
        // Shape creation logic
    }

    private void CreateJoints(NativeArray<PhysicsBody> bodies)
    {
        // Joint creation logic
    }

    private void ConfigureProperties(NativeArray<PhysicsBody> bodies)
    {
        // Property configuration logic
    }
}

Best Practices

Design

• Start simple, iterate complexity
• Test individual components first
• Document factory parameters
• Provide sensible defaults
• Allow configuration customization

Performance

• Use batch creation when possible
• Reuse definitions
• Pool complex objects
• Minimize allocations
• Cache shared geometries

Maintenance

• Keep factories modular
• Separate creation from configuration
• Use clear naming
• Comment complex logic
• Version control parameters

Debugging

• Add visual debugging
• Log creation steps
• Validate configurations
• Test edge cases
• Profile performance

Common Patterns

Procedural Generation

Generate variations:

• Randomize parameters
• Use seed for reproducibility
• Create unique instances
• Maintain factory template

Object Pooling

Reuse complex objects:

• Pre-create pool
• Reset on return
• Validate before reuse
• Manage pool size

Serialization

Save/load configurations:

• Export factory parameters
• Store object templates
• Load from files
• Runtime creation

Prefab-Like System

Template-based creation:

• Define templates
• Instantiate from template
• Override parameters
• Maintain template library

Advanced Techniques

Procedural Ragdolls

Generate ragdolls from skeletons:

• Parse skeleton structure
• Generate bodies from bones
• Auto-create joints
• Configure limits automatically

Soft Body Optimization

Reduce particle count:

• Variable resolution
• LOD for distance
• Simplify internal structure
• Optimize surface shapes

Vehicle Dynamics

Advanced vehicle behavior:

• Active suspension
• Traction control
• Differential simulation
• Aerodynamics

Related Skills

When users need information about:

• Joints for factories - Use unity-physicscore2d-joints
• Batch creation - Use unity-physicscore2d-batching
• Collision filtering - Use unity-physicscore2d-filtering
• Performance - Use unity-physicscore2d-performance

Worked Examples

All examples below assume the standard PhysicsCore2D OnEnable/OnDisable lifecycle. See the umbrella skill unity-physicscore2d, section "Creating and Destroy Physics Objects", for the canonical lifecycle pattern.

• examples/RagdollFactory.cs — factory pattern: static Create(world, origin, scale) returning a Ragdoll struct (head + torso + arms + legs assembled from capsule bodies and limit-clamped hinge joints, negative-group filter to prevent self-collision); ships with RagdollFactoryDemo : MonoBehaviour showing OnEnable/OnDisable wrapping.
• examples/SoftBodyFactory.cs — factory pattern: static Create(world, position, sides, scale, jointFrequency, jointDamping) returning a SoftBody struct (capsule ring + soft PhysicsFixedJoints with spring-like compliance); demo MonoBehaviour drops one into a chain-bounded chamber.
• examples/VehicleFactory.cs — factory pattern: static Create(world, position, ...) returning a Vehicle struct (chassis + 2 wheel bodies + 2 wheel joints with motor + spring suspension + travel limits); demo MonoBehaviour drives via arrow keys.