Add raygui integration and UI functionality for body selection

- Add raygui as git submodule in ext/raygui/
- Update Makefile to include raygui headers
- Extend RenderState with UI fields (selected_body_index, show_body_list, show_body_info)
- Implement render_body_list_ui() for scrollable body list panel
- Implement render_body_info_ui() for detailed body information panel
- Add 'B' key toggle for body list panel
- Integrate UI rendering into main render loop
- Initialize UI state in main()

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "ext/tomlc17"]
 	path = ext/tomlc17
 	url = https://github.com/cktan/tomlc17
+[submodule "ext/raygui"]
+	path = ext/raygui
+	url = https://github.com/raysan5/raygui.git

Makefile

@@ -1,6 +1,6 @@
 # Compiler and flags
 CXX = g++
-CXXFLAGS = -Wall -Wextra -g -ggdb3 -std=c++14 -I./src -isystem./ext/raylib/src -I./ext/tomlc17/src
+CXXFLAGS = -Wall -Wextra -g -ggdb3 -std=c++14 -I./src -isystem./ext/raylib/src -I./ext/tomlc17/src -I./ext/raygui/src
 LDFLAGS = -L./ext/raylib/src -lraylib -lm -lpthread -ldl -lrt -lX11
 
 # Directories

ext/raygui

@@ -0,0 +1 @@
+Subproject commit 9a1c183d8539e2470635b22f92bdaefaf5218aaa

src/main.cpp

@@ -35,6 +35,11 @@ void run_gui_simulation(SimulationState* sim) {
 
     RenderState render_state;
     setup_camera(&render_state);
+    
+    // Initialize UI state
+    render_state.selected_body_index = -1;  // No selection initially
+    render_state.show_body_list = false;
+    render_state.show_body_info = false;
 
     bool paused = false;
     double speed_multiplier = 1.0;
@@ -46,6 +51,7 @@ void run_gui_simulation(SimulationState* sim) {
     printf("  Space: Pause/Resume\n");
     printf("  +/-: Speed up/slow down simulation\n");
     printf("  I: Toggle info display\n");
+    printf("  B: Toggle body list\n");
     printf("  ESC: Quit\n\n");
 
     while (!WindowShouldClose()) {

src/renderer.cpp

@@ -3,6 +3,10 @@
 #include <cmath>
 #include <cstdio>
 
+// raygui implementation (header-only library)
+#define RAYGUI_IMPLEMENTATION
+#include "raygui.h"
+
 // Initialize raylib window
 void init_renderer(int width, int height, const char* title) {
     InitWindow(width, height, title);
@@ -68,6 +72,11 @@ void update_camera(RenderState* render_state) {
     if (IsKeyPressed(KEY_I)) {
         render_state->show_info = !render_state->show_info;
     }
+
+    // Toggle body list with B key
+    if (IsKeyPressed(KEY_B)) {
+        render_state->show_body_list = !render_state->show_body_list;
+    }
 }
 
 // Transform from simulation coordinates (XY plane) to render coordinates (XZ plane)
@@ -316,6 +325,10 @@ void render_simulation(SimulationState* sim, RenderState* render_state) {
         render_info(sim, "solar_system.txt");
     }
 
+    // Render UI panels
+    render_body_list_ui(sim, render_state);
+    render_body_info_ui(sim, render_state);
+
     EndDrawing();
 }
 
@@ -350,3 +363,133 @@ void render_info(SimulationState* sim, const char* config_name) {
     DrawText("  I: Toggle info", 10, 210, 14, LIGHTGRAY);
     DrawText("  ESC: Quit", 10, 230, 14, LIGHTGRAY);
 }
+
+// Render body list UI panel
+void render_body_list_ui(SimulationState* sim, RenderState* render_state) {
+    if (!render_state->show_body_list) return;
+
+    // Panel dimensions
+    int panel_width = 200;
+    int panel_height = 400;
+    int panel_x = 10;
+    int panel_y = 10;
+
+    Rectangle panel_bounds = { (float)panel_x, (float)panel_y, (float)panel_width, (float)panel_height };
+
+    // Create body list for raygui
+    const char** body_names = (const char**)malloc(sim->body_count * sizeof(char*));
+    if (!body_names) return;
+
+    for (int i = 0; i < sim->body_count; i++) {
+        body_names[i] = sim->bodies[i].name;
+    }
+
+    // Draw window
+    if (GuiWindowBox(panel_bounds, "Bodies")) {
+        render_state->show_body_list = false;
+    }
+
+    // Draw list view (inside window, leave space for title bar)
+    Rectangle list_bounds = { 
+        (float)panel_x + 4, 
+        (float)panel_y + 25, 
+        (float)panel_width - 8, 
+        (float)panel_height - 29 
+    };
+    
+    int focus = 0;
+    int active = 0;
+    if (render_state->selected_body_index >= 0 && render_state->selected_body_index < sim->body_count) {
+        focus = render_state->selected_body_index; // 0-based indexing for scroll
+        active = 1; // Mark as active
+    }
+    
+    int result = GuiListView(list_bounds, (const char*)body_names, &focus, &active);
+    
+    if (result >= 0 && result < sim->body_count) {
+        render_state->selected_body_index = result;
+        render_state->show_body_info = true;
+    }
+
+    free(body_names);
+}
+
+// Render body information UI panel
+void render_body_info_ui(SimulationState* sim, RenderState* render_state) {
+    if (!render_state->show_body_info || render_state->selected_body_index < 0 || 
+        render_state->selected_body_index >= sim->body_count) return;
+
+    // Panel dimensions
+    int panel_width = 250;
+    int panel_height = 300;
+    int panel_x = GetScreenWidth() - panel_width - 10;
+    int panel_y = 10;
+
+    Rectangle panel_bounds = { (float)panel_x, (float)panel_y, (float)panel_width, (float)panel_height };
+
+    CelestialBody* body = &sim->bodies[render_state->selected_body_index];
+
+    // Draw window
+    if (GuiWindowBox(panel_bounds, body->name)) {
+        render_state->show_body_info = false;
+    }
+
+    // Prepare info text
+    char info_text[1024];
+    char temp_buffer[256];
+
+    snprintf(info_text, sizeof(info_text), "Name: %s", body->name);
+    
+    snprintf(temp_buffer, sizeof(temp_buffer), "Mass: %.2e kg", body->mass);
+    strcat(info_text, "\n");
+    strcat(info_text, temp_buffer);
+    
+    snprintf(temp_buffer, sizeof(temp_buffer), "Radius: %.2e m", body->radius);
+    strcat(info_text, "\n");
+    strcat(info_text, temp_buffer);
+
+    // Position
+    snprintf(temp_buffer, sizeof(temp_buffer), "Position: (%.2e, %.2e, %.2e)", 
+             body->position.x, body->position.y, body->position.z);
+    strcat(info_text, "\n");
+    strcat(info_text, temp_buffer);
+
+    // Velocity
+    double vel_mag = vec3_magnitude(body->velocity);
+    snprintf(temp_buffer, sizeof(temp_buffer), "Velocity: %.2f m/s", vel_mag);
+    strcat(info_text, "\n");
+    strcat(info_text, temp_buffer);
+
+    // Orbital elements
+    snprintf(temp_buffer, sizeof(temp_buffer), "Eccentricity: %.3f", body->eccentricity);
+    strcat(info_text, "\n");
+    strcat(info_text, temp_buffer);
+
+    snprintf(temp_buffer, sizeof(temp_buffer), "Semi-major axis: %.2e m", body->semi_major_axis);
+    strcat(info_text, "\n");
+    strcat(info_text, temp_buffer);
+
+    // Parent body
+    if (body->parent_index >= 0 && body->parent_index < sim->body_count) {
+        snprintf(temp_buffer, sizeof(temp_buffer), "Parent: %s", sim->bodies[body->parent_index].name);
+    } else {
+        snprintf(temp_buffer, sizeof(temp_buffer), "Parent: None");
+    }
+    strcat(info_text, "\n");
+    strcat(info_text, temp_buffer);
+
+    // SOI
+    snprintf(temp_buffer, sizeof(temp_buffer), "SOI radius: %.2e m", body->soi_radius);
+    strcat(info_text, "\n");
+    strcat(info_text, temp_buffer);
+
+    // Draw info text (inside window, leave space for title bar)
+    Rectangle text_bounds = { 
+        (float)panel_x + 8, 
+        (float)panel_y + 25, 
+        (float)panel_width - 16, 
+        (float)panel_height - 29 
+    };
+    
+    GuiLabel(text_bounds, info_text);
+}

src/renderer.h

@@ -10,6 +10,9 @@ struct RenderState {
     double distance_scale;    // Scale factor for distances
     double size_scale;        // Scale factor for body sizes
     bool show_info;           // Display simulation info
+    int selected_body_index;  // -1 = no selection
+    bool show_body_list;      // Toggle for list panel
+    bool show_body_info;      // Toggle for info panel
 };
 
 // Renderer initialization and cleanup
@@ -26,6 +29,10 @@ void render_body(CelestialBody* body, RenderState* render_state);
 void render_simulation(SimulationState* sim, RenderState* render_state);
 void render_info(SimulationState* sim, const char* config_name);
 
+// UI rendering functions
+void render_body_list_ui(SimulationState* sim, RenderState* render_state);
+void render_body_info_ui(SimulationState* sim, RenderState* render_state);
+
 // Scaling functions
 Vector3 scale_position(Vec3 pos, double scale);
 float scale_radius(double radius, double scale);