Collider++

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Desc:

This project focuses on building a robust and efficient collision detection and resolution system for complex, non-trivial objects. It targets advanced shapes such as concave polygons and objects bounded by mathematical curves, going beyond basic line and convex geometry.

The engine will implement industry-standard techniques including Axis-Aligned Bounding Boxes (AABB), the Separating Axis Theorem (SAT), and spatial partitioning to achieve accurate and high-performance collision handling. Emphasis is placed on clean, efficient implementations and a clear separation between broad-phase and narrow-phase collision detection.

If time permits, the project will be extended with a basic physics system and a custom render pipeline using OpenGL to visualize geometry, collisions, and physical interactions.

Team

Name	GitHub ID	Role
Sathvik	VSathvikReddy	Lead
Anvesh	ElementSnow10	Lead
Akshat	Akshat-Chaplot	Lead
Aarav	aarav-prakash	Member
Kanishka	KanishkaDeveloper	Member
Dhivakar	cs25b023-collab	Member
Ananya	ananya-274	Member
Prajith	EntangledEquity	Member
Sathwik	ImagineLosing14	Member

Project Introduction

ColliderPP is a modular 2D collision engine built in C++ that simulates and visualizes real-time interactions between physical objects.

It features a data-driven architecture where objects are loaded from JSON, updated using kinematic equations, and interact through impulse-based collision resolution.

Motivation

This project was built to understand and implement the complete pipeline of a physics simulation engine—from data parsing and object modeling to real-time collision handling—without relying on external parsing libraries.

Key Features

• Real-time 2D collision simulation
• Custom-built JSON parser (mjson)
• Data-driven object initialization
• Modular architecture (engine, objects, collision, parsing separated)
• Impulse-based collision response
• Mass-weighted collision resolution
• Boundary collision handling
• Frame-based update system using delta time

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Architecture

ColliderPP is divided into two main subsystems:

1. Physics & Simulation Engine

Handles object lifecycle, physics updates, collision detection/resolution, and rendering.

2. Configuration System (mjson)

Parses JSON input and converts it into structured data used to initialize simulation objects at runtime.

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System Flow

config.json → mjson (Lexer → Parser → JObject) → Simulation Setup → Physics Engine Loop: → Collision Detection → Collision Resolution → Object Update → Rendering

Core Components

Entry Point (main.cpp)

• Initializes the simulator
• Loads configuration file
• Starts simulation loop

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Simulation Layer (simulation.cpp)

• Creates rendering window
• Loads objects from JSON
• Handles event loop and frame updates
• Tracks FPS

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Physics Engine (physics_engine.cpp)

• Maintains list of all objects

• Performs pairwise collision checks (O(n²))

• Resolves:

  • Object-object collisions
  • Boundary collisions

• Updates and renders objects

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Physics Object Base (physics_object.cpp)

• Abstract representation of physical entities

• JSON-based initialization

• Stores:

  • Position, velocity, acceleration
  • Angular properties
  • Physical attributes (mass, restitution, etc.)

• Uses explicit Euler integration:

  • velocity += acceleration × dt
  • position += velocity × dt

• Angular motion handled similarly

• Acceleration is reset each frame after integration

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Circle Implementation (physics_circle.cpp)

• Derived from PhysicsObject
• Represents circular bodies
• Syncs physics state with graphical representation

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Physical Attributes (physics_attributes.cpp)

Defines object behavior:

• Mass and angular mass
• Restitution (bounciness)
• Static/dynamic behavior
• Color mapping from string

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Collision System (collision.cpp)

Collision Pipeline

The collision system is divided into two distinct phases:

1. Detection
   Identifies whether two objects are intersecting

2. Resolution

   • Position correction (removes overlap)
   • Velocity update (applies physical response)

This separation ensures stable and predictable simulation behavior.

Collision Detection

• Circle-circle collision detection based on distance between object centers
• Detects overlap and computes collision normal

Position Correction

• Resolves overlap using mass-weighted displacement as heavier objects move less, improving physical realism.
• Prevents objects from sticking or penetrating

Velocity Resolution

• Ensures physically consistent response using conservation of momentum principles
• Skips resolution if objects are separating
• Uses collision normal projection to compute relative velocity
• Handles edge cases (zero distance)

Boundary Handling

• Detects collision with window edges
• Reflects velocity and clamps position

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Configuration System (mjson)

A lightweight custom JSON parser built from scratch.

Components

Lexer (lexer.cpp)

• Converts raw input into tokens

• Supports:

  • Strings, numbers, booleans
  • JSON symbols ({ } [ ] , :)

Parser (parser.cpp)

• Recursive descent parser

• Builds structured data:

  • Lists (vector<JObject>)
  • Dictionaries (unordered_map)

JObject (jobject.cpp)

• Unified representation of all JSON types

• Supports:

  • Type-safe conversions
  • Operator overloading (obj["key"])
  • Deep copy and move semantics

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File Structure

src/ ├── main.cpp ├── simulation.cpp ├── physics_engine.cpp ├── physics_object.cpp ├── physics_circle.cpp ├── physics_attributes.cpp ├── collision.cpp └── mjson/ ├── lexer.cpp ├── parser.cpp ├── jobject.cpp

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How to Run

Requirements

• C++ compiler (g++)
• SFML library installed

Compile and Execute

make run