claudes_game/docs/session_summaries/2026-01-07-rename-bodies-to-simulation-and-refactor-velocities.md

Rename bodies.h/cpp to simulation.h and Refactor Velocities (2026-01-07)

Changes Made

Refactored simulation module and velocity initialization:

1. Renamed files

   • src/bodies.h → src/simulation.h
   • src/bodies.cpp → src/simulation.cpp
   • Updated all include references in src/ and tests/
   • Updated Makefile to reference simulation.cpp
   • Updated documentation references

2. Moved simulation logic from config_loader to simulation

   • Moved calculate_initial_velocities() to simulation.cpp
   • Moved calculate_soi_radii() to simulation.cpp
   • Removed OrbitParams struct - use sim->bodies[i].fields directly
   • Config loader now only handles TOML parsing

3. Refactored calculate_initial_velocities()

   • Broke up 114-line function into 8 focused functions with descriptive names
   • Added vec3_cross() utility to physics.cpp for reusable cross product calculation
   • Made helper functions static in simulation.cpp (internal implementation detail)
   • Removed unnecessary helper declarations from simulation.h (cleaner public API)

New helper functions:

• compute_perpendicular_orbital_velocity() - root body orbits (26 lines)
• compute_orbital_velocity_from_vis_viva() - child body orbits (37 lines)
• compute_system_barycenter() - barycenter calculation (28 lines)
• compute_total_root_mass() - total mass calculation (8 lines)
• set_root_bodies_velocity() - sets all root velocities (15 lines)
• set_child_bodies_velocity() - sets all child velocities (13 lines)
• print_system_info_if_multiple_roots() - debug output (7 lines)

Main compute_initial_velocities() reduced from 114 to 10 lines.

4. Cleaned up public API
   • Removed helper function declarations from simulation.h
   • Only public API remains: compute_initial_velocities(), calculate_initial_velocities(), calculate_soi_radii()
   • Removed deprecated comment

Commits

1. 81e799c Rename bodies.h/cpp to simulation.h/cpp
2. 9aafbd5 Refactor velocity initialization into smaller functions
3. aa8a6b9 Merge branch 'loading-refactor' - refactor velocity initialization

Results

16 files changed, +200/-212 lines (net -12 lines)

Net line changes:

• config_loader.cpp: 330 → 143 lines (-187)
• config_loader.h: 22 → 16 lines (-6)
• physics.cpp: 123 → 131 lines (+8)
• physics.h: 38 → 39 lines (+1)
• simulation.cpp: 187 → 350 lines (+163)
• simulation.h: 56 → 62 lines (+6)

All builds and tests pass (24 assertions, 5 test cases).

Benefits:

• Code reuse: vec3_cross() used 2x (eliminates duplicate perpendicular velocity logic)
• Testability: smaller functions easier to test individually
• Readability: descriptive function names for each body type scenario
• Maintainability: main function reduced from 114 to 10 lines (91% reduction)
• Better separation of concerns: config_loader only parses TOML, simulation handles physics