Stellar Engine

A lightweight 2D physics engine written in C++. Stellar provides a simple and efficient foundation for physics-based games and simulations.

Quick Start

Prerequisites

• C++ compiler with C++11 support
• SDL2 library

Installation

macOS (using Homebrew)

brew install sdl2

Linux (Debian/Ubuntu)

sudo apt-get install libsdl2-dev

Building

# Build with SDL2 visualization
g++ test_game.cpp -std=c++11 -o game -I/opt/homebrew/include -L/opt/homebrew/lib -lSDL2

Running the Demo

./game

Usage Example

int main() {
  World world;
  initWorld(world);

  int circleId = addCircle(world, {0, 10}, 1.0, 1.0);
  int boxId = addBox(world, {5, 10}, {2, 2}, 2.0);

  Body &circle = world.bodies[circleId];
  std::cout << "Circle area: " << calculateArea(circle) << "\n";
  std::cout << "Circle MOI: " << calculateMOI(circle) << "\n";

  double fixedTimeStep = 1.0 / 60.0; // 60 Hz simulation
  for (int i = 0; i < 100; i++) {
    stepWorld(world, fixedTimeStep);

    std::cout << "Step " << i << ":\n";
    std::cout << "Circle position: " << world.bodies[circleId].position.x
              << ", " << world.bodies[circleId].position.y << "\n";
    std::cout << "Box position: " << world.bodies[boxId].position.x << ", "
              << world.bodies[boxId].position.y << "\n\n";
  }

  return 0;
}

ToDo

Phase 1: Core Mathematics and Basic Motion

Vector Operations

Vector Implementations are Done!

• Vector2D struct definition (x, y components)
• Vector operation functions:
  • vec2_add, vec2_sub, vec2_mul
  • vec2_dot, vec2_cross
  • vec2_normalize
  • vec2_rotate
  • vec2_length, vec2_length_squared

Basic Motion Implementation is Done!

Basic Motion

• Body struct (position, velocity, acceleration)
• Force functions:
  • apply_force
  • apply_impulse
• Integration functions:
  • integrate_linear_motion
  • apply_gravity
• World struct to hold all bodies

Phase 2: Shapes and Collision Detection

Basic Shapes

• Circle struct (position, radius)
• AABB struct (min, max points)
• Polygon struct (vertex array, vertex count)
• Shape union struct with type enum
• Point containment test functions

Collision Detection

• Broad phase functions:
  • grid_system struct and functions
  • quadtree struct and functions
• Collision pair struct
• Narrow phase functions:
  • check_circle_circle
  • check_aabb_aabb
  • check_circle_aabb
  • check_polygon_polygon (SAT)

Phase 3: Collision Response

Basic Resolution

• Contact struct (normal, depth, points)
• Resolution functions:
  • resolve_collision_positions
  • resolve_collision_velocities
  • apply_momentum_conservation
  • resolve_penetration

Material Properties

• Material struct:
  • restitution
  • friction_static
  • friction_dynamic
  • density
• Material resolution functions

Phase 4: Constraints

Basic Constraints

• Constraint struct with type enum
• Constraint functions:
  • solve_distance_constraint
  • solve_point_constraint
  • solve_rotation_constraint
  • solve_angle_limits

Advanced Joints

• Spring struct and functions
• Rope struct and functions
• Joint struct variations
• Joint solver functions

Phase 5: Advanced Features

Forces and Effects

• Force generator struct
• Force application functions:
  • apply_drag
  • apply_buoyancy
  • apply_wind
• Raycast struct and functions

Performance Optimization

• Body state flags (active/sleeping)
• Island struct for connected bodies
• Continuous collision functions
• Spatial partitioning optimization

Phase 6: Special Features

Soft Body Physics

• Spring-mass struct
• Soft body solver functions
• Cloth struct and functions
• Rope simulation functions

Particles

• Particle struct
• Particle system functions
• Particle emitter struct
• Fluid particle functions