claudes_game/docs/session_summaries/2026-01-18-config-display-and-rendering-fixes.md

Session Summary: Config Display, Compiler Warnings, Orbit Rendering Fix, and Camera Initialization

Date

2026-01-18

Overview

Fixed multiple UI and rendering issues: added config file name display, resolved compiler warnings, corrected orbit rendering for nested bodies (moons), and initialized camera to follow root body on startup.

Key Features Implemented

1. Config File Name Display

• Added char config_name[256] field to SimulationState struct
• Config file path now stored when loaded via load_system_config()
• Displayed in simulation info panel under "Config:" label
• Eliminates hardcoded "solar_system.txt" reference

Before: Info panel always showed "solar_system.txt" regardless of actual config After: Shows actual loaded config path (e.g., "tests/configs/solar_system.toml")

2. Compiler Warning Fixes

• Removed unused departure_period variable from calculate_hohmann_transfer()
• Removed unused sun variable from spawn_spacecraft_on_transfer()
• Increased temp_buffer size from 256 to 512 in render_info() to prevent truncation warning

Result: Clean build with zero compiler warnings

3. Orbit Rendering Fix for Nested Bodies

• Changed render_orbit() to use local_velocity instead of global velocity
• Critical fix for correct moon and satellite orbit paths

Technical Details:

• Planets: local_velocity ≈ global_velocity (orbits around Sun)
• Moons: local_velocity is velocity relative to parent planet
• Prior fix: local_velocity used for physics integration, but global_velocity used for orbit rendering
• Current fix: Both physics and rendering now use local_velocity

Impact:

• Moon orbits now render correctly around their parent planets
• Future satellites will render correctly around moons
• Parabolic and hyperbolic orbit types also fixed

4. Camera Initialization on Root Body

• Camera now automatically selects root body (star) on startup
• Camera follow mode enabled by default for root body
• body_list_active synchronized with selected_body_index
• Default camera offset (0, 50, 100) applied relative to root body

Before: No body selected, camera in neutral position After: Camera follows root body (e.g., Sun) immediately on startup

Technical Details

SimulationState Structure Changes

struct SimulationState {
    CelestialBody* bodies;
    int body_count;
    int max_bodies;
    double time;
    double dt;
    char config_name[256];    // NEW: name of the config file loaded
};

Config Loading

// In load_system_config()
strncpy(sim->config_name, filepath, sizeof(sim->config_name) - 1);
sim->config_name[sizeof(sim->config_name) - 1] = '\0';

Orbit Rendering Fix

// Before (incorrect for moons)
Vec3 r_vec = vec3_sub(body->position, parent->position);
double v = vec3_magnitude(body->velocity);  // Global velocity
double r_dot_v = r_vec.x * body->velocity.x + ...

// After (correct for all bodies)
Vec3 r_vec = vec3_sub(body->position, parent->position);
Vec3 v_vec = body->local_velocity;  // Local velocity relative to parent
double v = vec3_magnitude(v_vec);
double r_dot_v = r_vec.x * v_vec.x + ...

Camera Initialization

// Find root body
int root_body_index = -1;
for (int i = 0; i < sim->body_count; i++) {
    if (sim->bodies[i].parent_index == -1) {
        root_body_index = i;
        break;
    }
}

// Initialize with root body selected
render_state.selected_body_index = root_body_index >= 0 ? root_body_index : -1;
render_state.body_list_active = root_body_index >= 0 ? root_body_index : -1;
render_state.camera_follow_body = root_body_index >= 0;

Files Modified

Core Implementation

• src/simulation.h - Added config_name field to SimulationState
• src/simulation.cpp - Initialize config_name to empty string in create_simulation()
• src/config_loader.cpp - Store config filepath in sim->config_name
• src/renderer.h - Removed config_name parameter from render_info()
• src/renderer.cpp - Display config name, use local_velocity for orbit rendering, increase buffer size
• src/main.cpp - Find root body and initialize camera selection/follow state

Commits Summary

1. c4262ab - Store and display config file name in simulation state
2. 8f60ba5 - Fix compiler warnings: remove unused variables, increase buffer size
3. 8278cb0 - Fix orbit rendering to use local_velocity for nested orbits
4. c3a4606 - Initialize camera to follow root body on startup

Testing Status

All changes compiled and tested:

• ✅ Config file name displayed correctly in UI
• ✅ Zero compiler warnings in full rebuild
• ✅ Moon orbit paths render correctly around parent planets
• ✅ Planet orbit paths remain correct
• ✅ Camera follows root body on startup
• ✅ Tests pass (23/24, with 1 pre-existing Hohmann transfer test failure)

Branch Status

Working branch: main Clean working tree ready for next session.

Future Enhancements

Potential Improvements

• Visual highlighting of selected body in 3D view
• Camera focus indicator (show which body is being followed)
• Search/filter functionality in body list
• Reference frame switching (view from body's perspective)

Bug Follow-ups

• Investigate Hohmann transfer test failure (energy drift > 200%)