# SOI Bug Fix and Dynamic Orbital Rendering (2026-01-05)

## Changes Made

### Core Bug Fixes
- Fixed SOI calculation bug: was using current distance instead of orbital semi_major_axis
  - Caused incorrect SOI radii for eccentric orbits (e.g., comet at perihelion vs aphelion)
  - Now properly uses stored orbital parameter from config file
- Added parent change tracking to headless simulation mode for debugging SOI transitions

### Test Refactoring
- Refactored test to use same code path as simulation via `load_system_config()`
  - Eliminated ~30 lines of manual body setup in test
  - Ensures test and simulation behave identically
- Added `config_loader.cpp` to test build dependencies
- Refactored verbose test output into separate functions with compile-time flag
  - Added `COMET_TEST_VERBOSE_OUTPUT` flag (default: 0)
  - Moved output to `print_orbital_snapshots()` and `print_parent_changes()`

### Graphics Enhancements
- Implemented dynamic orbital rendering with real-time element calculation
  - Orbits now update automatically when parent body changes
  - Calculates orbital elements from current position/velocity relative to parent
- Added support for parabolic trajectories (e ≈ 1)
  - Limited to ±86° from periapsis to avoid infinite vertices
- Added support for hyperbolic trajectories (e > 1)
  - Limited to asymptotic angle to avoid infinite vertices
- Properly orients orbits in 3D space using eccentricity vector and angular momentum

### Code Structure
Refactored renderer for separation of concerns:
- `OrbitalBasis` struct - Holds orbital reference frame
- `calculate_orbital_basis()` - Computes periapsis direction, normal, and perpendicular vectors
- `orbital_to_cartesian()` - Transforms 2D orbital coordinates to 3D space
- `draw_orbit_segment()` - Handles rendering of individual line segments
- `render_elliptical_orbit()` - Draws closed elliptical paths (100 segments)
- `render_hyperbolic_orbit()` - Draws open hyperbolic/parabolic paths (60 segments)

### Test Configuration
Enhanced `configs/test_simple.txt` with diverse orbit examples:
- Parabolic object (e=1.0 at 0.5 AU, exactly at escape velocity)
- Inclined asteroid (circular orbit with 30° inclination)
- Hyperbolic visitor (e=1.5, interstellar trajectory)

## Commits

- `89931c3` Fix SOI calculation and orbit direction bugs
- `8e21f71` Refactor test to use same code path as simulation
- `232614d` Revert cross product direction in config_loader
- `4a313f8` remove extra debugging not added by claude (user commit)
- `c613d21` Refactor verbose test output to separate functions
- `060ff40` Add dynamic orbital rendering with hyperbolic/parabolic support
- `e1df0b4` Add diverse orbit examples to test_simple config

## Results

7 files changed, +209/-106 (net +103 lines)

### Key Findings
- Simulation and test now show identical behavior (parent change Sun→Mars at day 1532)
- Comet enters Mars's SOI at 0.003787 AU (just within 0.003792 AU SOI radius)
- Comet is ejected from solar system after Mars encounter (ends at 58.7 AU with e=1.0)
- Renderer now correctly displays elliptical, parabolic, and hyperbolic trajectories
- Orbits update dynamically when gravitational parent changes

### Test Results
All tests passing (21 assertions in 5 test cases) ✓

## Outstanding Issues

- Comet remains Mars's child after leaving Mars's SOI
  - `find_dominant_body()` doesn't check if body is still within current parent's SOI
  - Should switch back to grandparent (Sun) when exiting child SOI
  - Results in comet staying as Mars-relative even after ejection