Improve collision system with support for multiple shapes

[Linux0Hat]

Improve collision system with support for multiple shapes

Overview

Currently, the physics engine only supports circular objects for collision detection. This enhancement will add support for multiple shapes including rectangles, polygons, and potentially other geometric forms, along with improved collision algorithms.

Current State Analysis

From the existing code in src/lib.rs, the collision system:

• Only handles circle-to-circle collisions
• Uses basic distance-based collision detection
• Has collision response with restitution coefficients
• Supports frozen objects

Proposed Improvements

1. Shape System Architecture

#[derive(Clone, Serialize, Deserialize)]
pub enum Shape {
    Circle { radius: f64 },
    Rectangle { width: f64, height: f64 },
    Polygon { vertices: Vec<(f64, f64)> },
    // Future: Ellipse, Capsule, etc.
}

2. Enhanced Object Structure

• Modify the Object struct to include a Shape field instead of just radius
• Add rotation angle for non-circular shapes
• Include moment of inertia calculations for proper rotational physics

3. Collision Detection Algorithms

Circle-Circle (Current - Improve)

• Optimize the existing implementation
• Better handling of edge cases

Circle-Rectangle

• Implement closest point on rectangle to circle center
• Handle corner cases properly

Rectangle-Rectangle

• Separating Axis Theorem (SAT) implementation
• AABB (Axis-Aligned Bounding Box) optimization for axis-aligned rectangles

Circle-Polygon & Polygon-Polygon

• SAT for convex polygons
• GJK algorithm for more complex cases

4. Collision Response Improvements

• Rotational dynamics: Objects should rotate upon collision
• Contact point calculation: More accurate collision response based on contact points
• Friction simulation: Add surface friction between objects
• Multiple contact points: Handle scenarios where objects have multiple contact points

5. Performance Optimizations

• Broad phase collision detection: Spatial partitioning (quadtree/grid)
• Bounding box pre-checks: Quick elimination of non-colliding pairs
• Shape-specific optimizations: Fast paths for common cases

Technical Implementation Plan

Phase 1: Core Shape System

• Define Shape enum and update Object structure
• Implement basic rendering for different shapes in WorldView
• Add rotation support to objects

Phase 2: Collision Detection

• Implement circle-rectangle collision detection
• Add rectangle-rectangle collision (AABB first, then oriented)
• Create polygon collision detection using SAT

Phase 3: Enhanced Collision Response

• Add rotational physics (angular velocity, moment of inertia)
• Implement contact point calculation
• Add friction coefficients and simulation

Phase 4: Performance & Polish

• Implement broad-phase collision detection
• Add spatial partitioning for better performance
• Optimize hot paths in collision code

API Changes

Breaking Changes

• add_object method will need to accept a Shape parameter instead of radius
• Serialization format will change (consider migration strategy)

New Methods

// Shape creation helpers
pub fn add_circle_object(&mut self, pos_x: f64, pos_y: f64, radius: f64, ...);
pub fn add_rectangle_object(&mut self, pos_x: f64, pos_y: f64, width: f64, height: f64, ...);
pub fn add_polygon_object(&mut self, pos_x: f64, pos_y: f64, vertices: Vec<(f64, f64)>, ...);

// Rotation methods
pub fn set_object_rotation(&mut self, index: usize, angle: f64);
pub fn set_object_angular_velocity(&mut self, index: usize, angular_vel: f64);

Testing Strategy

• Unit tests for each collision detection algorithm
• Integration tests with various shape combinations
• Performance benchmarks comparing old vs new system
• Visual tests to ensure collision responses look realistic

Backward Compatibility

• Provide migration path for existing circular objects
• Maintain current API with deprecation warnings
• Ensure existing web interface continues to work

Additional Considerations

• Impact on WASM bundle size
• Performance implications for browser rendering
• Memory usage with more complex shape data
• Integration with the planned ratatui interface