claudes_game/docs/sessions/2026-01-03-config-improvements.md

Config File Improvements & Main.cpp Refactoring

Date: 2026-01-03

Overview

This session focused on refactoring main.cpp into smaller functions and adding support for eccentric orbits through an extended configuration file format.

Changes Made

1. Main.cpp Refactoring

Broke down 215-line main() function into focused, reusable functions:

New Functions:

• parse_command_line_args() - Parse CLI args into ProgramArgs struct
• print_startup_info() - Display simulation configuration
• run_headless_simulation() - Terminal-based simulation with state capture
• run_gui_simulation() - 3D visualization mode

Result: main() now only ~25 lines (setup and dispatch)

Additional Improvements:

• Added initial state capture in headless mode
• Initial state now printed both at start AND end for comparison
• Cleaner separation of concerns

2. Eccentric Orbit Support

Extended config format from 10 to 12 fields:

Old Format (10 fields):

name mass radius x y z parent_index r g b

New Format (12 fields):

name mass radius x y z parent_index r g b eccentricity semi_major_axis

Implementation:

• Uses vis-viva equation: v = sqrt(G*M*(2/r - 1/a))
• Circular orbits: e=0, a=orbital_radius
• Elliptical orbits: e>0, a=semi_major_axis
• Unified code path for both orbit types

Example Configurations:

# Circular orbit
Earth 5.972e24 6.371e6 1.496e11 0 0 0 0.0 0.5 1.0 0 1.496e11

# Eccentric orbit (e=0.7)
Comet 1e14 5e3 1.122e11 0 0 0 0.5 0.8 1.0 0.7 3.74e11

3. Code Simplification

• Removed dual format parsing (now single unified format)
• Shortened function name: calculate_initial_velocities_with_params() → calculate_velocities()
• Removed OrbitParams.has_params field (always have params now)
• Cleaner velocity calculation logic

4. Testing

Created test_simple.txt with eccentric comet:

• Eccentricity: 0.7
• Semi-major axis: 2.5 AU
• Perihelion: 0.75 AU
• Aphelion: 4.25 AU

Test Results:

• ✓ Initial velocity: 44.849 km/s (matches theoretical)
• ✓ Position varies from 0.75 AU to ~3.8 AU over simulation
• ✓ Velocity varies from 44.8 km/s (perihelion) to 10.6 km/s (aphelion)
• ✓ Energy conservation maintained

5. Documentation Updates

README.md:

• Updated config format section with 12-field format
• Added examples for both circular and eccentric orbits
• Added "Eccentric orbit support" to features list
• Updated field descriptions

docs/config_assumptions.md:

• Documented fixed issues (eccentric orbits, main.cpp refactoring)
• Updated format assumptions (10 → 12 fields)
• Added prioritized TODO list
• Added session notes with detailed change log

Git Commits

1. e5da7aa - Refactor main.cpp into focused functions

   • Extracted argument parsing, headless sim, GUI sim
   • Added initial state capture for comparison

2. 17f11bb - Add eccentric orbit support with unified config format

   • Extended format to 12 fields
   • Implemented vis-viva equation
   • Added example comet configuration

3. 8b9a06e - Update documentation for eccentric orbit support

   • Updated README with new format
   • Updated config_assumptions.md

4. 61ac1c5 - Add session notes and TODOs to config documentation

   • Documented all session changes
   • Created prioritized action items

Files Modified

Source Code:

• src/main.cpp (refactored into functions)
• src/config_loader.cpp (added orbit parameters support)

Configuration:

• configs/test_simple.txt (updated to 12-field format + comet)

Documentation:

• README.md (new format examples)
• docs/config_assumptions.md (status updates + TODOs)

Known Issues & TODOs

HIGH PRIORITY:

• Update configs/solar_system.txt to new 12-field format
• Update configs/example_binary_star.txt to new 12-field format
• Fix Moon position in solar_system.txt
  • Current: (1.500e11, 0, 0) - 4 million km from Earth
  • Should: (~1.496e11 + 3.844e8, 0, 0) - 384,400 km from Earth
• Fix Jupiter's moons positions (same issue as Moon)

MEDIUM PRIORITY:

• Add config file validation
• Document coordinate system clearly (absolute vs relative)

LOW PRIORITY:

• Consider relative coordinate option for child bodies
• Add 3D orbit support (currently XY plane only)

Technical Notes

Vis-Viva Equation

v = sqrt(G*M*(2/r - 1/a))

Where:

• v = orbital velocity at current position
• G = gravitational constant
• M = parent body mass
• r = current distance from parent
• a = semi-major axis of orbit

For circular orbits (e=0):

• r = a (constant)
• Equation simplifies to: v = sqrt(G*M/r)

For eccentric orbits (e>0):

• At perihelion (r = a(1-e)): velocity is maximum
• At aphelion (r = a(1+e)): velocity is minimum
• Demonstrates Kepler's 2nd law (equal areas in equal times)

Orbital Period:

T = 2π * sqrt(a³/GM)

Example for comet (a=2.5 AU): T ≈ 1444 days

Testing Commands

Build:

make

Run with default config (currently test_simple.txt):

./orbit_sim

Run headless for 1000 days:

./orbit_sim --days 1000

Run with specific config:

./orbit_sim configs/test_simple.txt

Run headless with readable units:

./orbit_sim --headless --readable --days 365

Next Session Recommendations

1. Update remaining config files to 12-field format
2. Fix moon positions with correct physics
3. Test updated configurations
4. Consider adding config validation warnings
5. Possibly add argument of periapsis parameter for 3D orbit orientation