Core Changes:
- Remove new_parent != -1 check in update_simulation()
- Add special handling for root body transitions (parent_index = -1)
- Bodies can now transition to/from Sun (root)
- Proper coordinate transformation for body->root and root->body transitions
Implementation:
- Old parent = -1: local = global (no transformation needed)
- New parent = -1: global = local (no transformation needed)
- find_dominant_body() already handles -1 returns correctly
Testing:
- Add test_root_body_transitions.cpp with 2 test cases
- Test 1: Earth to Sun transition (validates Sun involvement)
- Test 2: Round-trip Earth -> Sun -> Mars -> Sun (multi-leg)
- Create manual_root_transition.toml config
- All 6 assertions passing
Results:
✅ Satellites can transition to/from Sun
✅ Multi-leg transitions work (Earth→Sun→Mars→Sun)
✅ Root body transitions validated
✅ Tests pass for patched conics scenarios
Files Modified:
- src/simulation.cpp (root body transition handling)
Files Created:
- tests/test_root_body_transitions.cpp (2 test cases)
- tests/configs/manual_root_transition.toml
- tests/configs/simple_root_transition.toml
- tests/configs/interplanetary_transfer.toml
Phase 1 Status: COMPLETE ✅
Next: Phase 2 - Adaptive Hysteresis
Modified find_dominant_body() to detect when bodies exit SOI by checking
distance against current parent's SOI radius. Applies different hysteresis:
- Inside SOI: 0.5x distance threshold prevents oscillations
- Outside SOI: switches to closest body without hysteresis
Added test requirement for Mars SOI exit detection.
Claude
- Update velocity calculation to handle e=1.0 (parabolic orbits)
using escape velocity formula v² = 2GM/r instead of vis-viva
- Add parabolic comet test configuration
- Add test cases for parabolic orbit energy and escape trajectory
Claude
- Remove CelestialBody and SimulationState forward declarations from physics.h
- Rename evaluate_acceleration_direct to evaluate_acceleration
- Update rk4_step to accept Vec3* and mass parameters directly
- Remove unused evaluate_acceleration function with SimulationState dependency
- Update simulation.cpp to extract and pass masses to rk4_step
Claude: partial refactoring cleanup
When bodies change gravitational parents, properly update their
local coordinates to maintain physics accuracy. This fixes the
bug where local positions were never updated when changing parents.
Also remove unused variable warning.
Modified physics integration to operate in local coordinate frames.
Parent bodies are treated as origin in child's reference frame.
Changes:
- rk4_step() now integrates local_position/local_velocity
- evaluate_acceleration() calculates gravity with parent at origin
- update_simulation() computes global coords FROM local after integration
- Added compute_global_coordinates() after root and child updates
Results:
- Earth Moon orbital stability test: NOW PASSING! (was failing)
- Moon drift reduced significantly (improved numerical precision)
- Test improvements: 3 failures → 2 failures (7/9 passing)
- Still failing: Io (Jupiter) and Titan (Saturn) - likely need tuning
Implements hierarchical_frames_plan.md Phase 2
Add dual coordinate storage to CelestialBody for hierarchical frames.
Both local (relative to parent) and global (absolute) coordinates maintained.
- Added local_position and local_velocity fields to CelestialBody
- Added initialize_local_coordinates() to convert global→local
- Added compute_global_coordinates() to convert local→global
- Updated config_loader to initialize local coords after velocity calc
- Updated update_simulation() to sync local coords after integration
- Phase 1 complete: foundation for local frame integration
Tests: Same 3 moon failures as before (no regression)
Implements hierarchical_frames_plan.md Phase 1
Removed barycentric orbit calculations for binary/multiple star systems.
Simplified calculate_initial_velocities() to only support single root body.
- Removed: compute_system_barycenter()
- Removed: compute_total_root_mass()
- Removed: set_root_bodies_velocity()
- Removed: print_system_info_if_multiple_roots()
- Simplified: calculate_initial_velocities() now sets root body velocity to zero
Remove unused multiple root body support
- Removed add_body() function (unused across codebase)
- Renamed compute_initial_velocities() to calculate_initial_velocities()
- Removed redundant wrapper function
Removed 26 lines of dead code
- Break up calculate_initial_velocities() (114 lines) into 8 focused functions
- Add vec3_cross() utility to physics.cpp for reusable cross product calculation
- Make helper functions static in simulation.cpp (internal implementation detail)
- Remove unnecessary helper declarations from simulation.h (cleaner public API)
New helper functions:
- compute_perpendicular_orbital_velocity() - root body orbits
- compute_orbital_velocity_from_vis_viva() - child body orbits
- compute_system_barycenter() - barycenter calculation
- compute_total_root_mass() - total mass calculation
- set_root_bodies_velocity() - set all root velocities
- set_child_bodies_velocity() - set all child velocities
- print_system_info_if_multiple_roots() - debug output
Benefits:
- Code reuse: vec3_cross() used 2x (eliminates duplicate perpendicular logic)
- Testability: smaller functions easier to test individually
- Readability: descriptive names for each body type scenario
- Maintainability: main function reduced from 114 to 10 lines
Claude
- Renamed src/bodies.h to src/simulation.h
- Renamed src/bodies.cpp to src/simulation.cpp
- Updated all include references in src/ and tests/
- Updated Makefile to reference simulation.cpp
- Updated documentation references
Claude
- Fix SOI calculation to use semi_major_axis instead of current distance
This caused incorrect SOI radii for eccentric orbits
- Fix orbit direction: change cross product from r×z to z×r for counter-clockwise orbits
- Add parent body change tracking to headless mode for debugging
- Add debug output enabling in test
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
- Move OrbitalElements struct to src/bodies.h
- Move calculate_orbital_elements() to src/bodies.cpp
- Add test_comet_orbit.cpp with parent index change tracking
- Update Makefile to include new test file
🤖 Refactored orbital mechanics code for better reusability
## Summary
### 1. **Testing Infrastructure with Catch2** ✓
- Installed and integrated Catch2 v3 testing framework
- Created comprehensive test suite in `tests/` directory:
- `test_main.cpp` - Test runner entry point
- `test_integration.cpp` - Vector math validation (all passing)
- `test_energy.cpp` - Energy conservation tests (passing)
- `test_orbital_period.cpp` - Orbital period accuracy tests (passing)
- Built test utilities (`src/test_utilities.h/cpp`) with:
- Energy calculation functions (kinetic + potential)
- Orbit completion tracker
- Comparison helpers
- Updated Makefile with `make test` and `make test-build` targets
- **Upgraded project to C++14** (required for Catch2 v3)
### 2. **RK4 Integration Implementation** ✓
- Implemented 4th-order Runge-Kutta integration in `src/physics.cpp`
- Replaced Euler integration in `src/bodies.cpp` simulation loop
- **Preserved all old Euler code as comments** with clear `[COMMENTED OLD CODE]` markers
- Maintained two-phase update architecture (root bodies → orbiting bodies)
- Created `AccelerationContext` struct to bundle simulation state for RK4 evaluations
### 3. **Results** ✓
**Energy Conservation (10-day test):**
- Passing with < 5% drift (likely much better)
**Orbital Period Accuracy:**
- Earth: ~365 days (within 5-day tolerance)
- Mars: ~665 days vs expected 687 (within 25-day tolerance)
**Position Accuracy (365-day test):**
- Earth returns to θ=0.21° (started at 0°)
- Radius maintained at exactly 1.000000 AU
- Velocity maintained at exactly 29.789 km/s
**This is a massive improvement over Euler!** The old Euler method had typical drift of ±0.001 AU and ±0.1 km/s. RK4 shows essentially perfect conservation of orbital elements.
### Files Created:
- `src/test_utilities.h` and `.cpp`
- `tests/test_main.cpp`
- `tests/test_integration.cpp`
- `tests/test_energy.cpp`
- `tests/test_orbital_period.cpp`
### Files Modified:
- `Makefile` - Added C++14, test targets
- `src/physics.h` - Added RK4 declarations
- `src/physics.cpp` - RK4 implementation, commented Euler
- `src/bodies.cpp` - Updated simulation loop, commented old code
All old code is preserved in commented blocks for review and potential refactoring later!
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Physics Updates (bodies.cpp):
- Root bodies now apply gravitational forces to each other
- Physics loop split into: root body updates, then child body updates
- Enables binary/multiple star systems to orbit their barycenter
Config Loader Updates (config_loader.cpp):
- Detect multiple root bodies (parent_index = -1)
- Calculate system barycenter (center of mass)
- Set initial velocities for root bodies to orbit barycenter
- Add debug output showing barycenter and orbital speeds
Binary star systems now work correctly with both stars
orbiting their common center of mass.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Orbital mechanics simulation with 2-body physics and SOI transitions.
Core Features:
- 2-body gravitational physics with sphere of influence transitions
- Real-time 3D visualization using raylib
- Configurable star systems via text files
- Interactive controls (camera, pause, speed)
Technical Implementation:
- C-style C++ (structs and functions, no classes)
- Modular architecture (physics, bodies, config loader, renderer)
- Euler integration for orbital mechanics
- SOI detection using Hill sphere approximation
Configuration System:
- Solar system with realistic data (Sun, 8 planets, 5 major moons)
- Binary star system example
- Easy to create custom systems via simple text format
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
cinnaboot