Add camera follow feature for selected body

Features:
- Add camera_follow_body flag to RenderState
- Update update_camera() to follow selected body when enabled
- F key toggles camera follow (requires body selected)
- Camera still rotates and zooms around followed body
- Removed old focus_camera() function (superseded by new implementation)
- Updated help text to show F key for camera follow toggle

Technical details:
- Camera target updates to body position each frame when following
- Existing rotation/zoom controls work relative to new target position
- Maintains orbital camera control pattern

src/main.cpp

@@ -42,6 +42,7 @@ void run_gui_simulation(SimulationState* sim) {
     render_state.show_body_info = false;
     render_state.body_list_scroll = 0;     // Initial scroll position
     render_state.body_list_active = -1;    // No active item initially
+    render_state.camera_follow_body = false; // Camera not following initially
 
     bool paused = false;
     double speed_multiplier = 1.0;
@@ -54,6 +55,7 @@ void run_gui_simulation(SimulationState* sim) {
     printf("  +/-: Speed up/slow down simulation\n");
     printf("  I: Toggle info display\n");
     printf("  B: Toggle body list\n");
+    printf("  F: Toggle camera follow on selected body\n");
     printf("  ESC: Quit\n\n");
 
     while (!WindowShouldClose()) {
@@ -80,18 +82,7 @@ void run_gui_simulation(SimulationState* sim) {
             }
         }
 
-#if 0
-        /****
-        * Hacks ahead...
-        */
-        int focus_index = 4;  // earth: 2, jupiter, 4
-        if (sim->body_count >= focus_index) {
-            Vector3 offset = {0, 2, 10};
-            focus_camera(&render_state, &sim->bodies[focus_index], offset);
-        }
-#else
-        update_camera(&render_state);
-#endif
+        update_camera(&render_state, sim);
 
         render_simulation(sim, &render_state);
     }

src/renderer.cpp

@@ -7,6 +7,9 @@
 #define RAYGUI_IMPLEMENTATION
 #include "raygui.h"
 
+// Forward declarations
+static Vector3 sim_to_render(Vec3 pos, double scale);
+
 // Initialize raylib window
 void init_renderer(int width, int height, const char* title) {
     InitWindow(width, height, title);
@@ -33,7 +36,15 @@ void setup_camera(RenderState* render_state) {
 }
 
 // Update camera with keyboard/mouse controls
-void update_camera(RenderState* render_state) {
+void update_camera(RenderState* render_state, SimulationState* sim) {
+    // If following a body, update target to body position
+    if (render_state->camera_follow_body && render_state->selected_body_index >= 0 &&
+        render_state->selected_body_index < sim->body_count) {
+        CelestialBody* body = &sim->bodies[render_state->selected_body_index];
+        Vector3 body_pos = sim_to_render(body->position, render_state->distance_scale);
+        render_state->camera.target = body_pos;
+    }
+
     // Orbital camera rotation with arrow keys
     float camera_distance = Vector3Distance(render_state->camera.position, render_state->camera.target);
     float angle_speed = 0.02f;
@@ -77,6 +88,16 @@ void update_camera(RenderState* render_state) {
     if (IsKeyPressed(KEY_B)) {
         render_state->show_body_list = !render_state->show_body_list;
     }
+
+    // Toggle camera follow with F key
+    if (IsKeyPressed(KEY_F)) {
+        if (render_state->selected_body_index >= 0) {
+            render_state->camera_follow_body = !render_state->camera_follow_body;
+            printf("Camera follow: %s\n", render_state->camera_follow_body ? "enabled" : "disabled");
+        } else {
+            render_state->camera_follow_body = false;
+        }
+    }
 }
 
 // Transform from simulation coordinates (XY plane) to render coordinates (XZ plane)
@@ -89,11 +110,7 @@ Vector3 sim_to_render(Vec3 pos, double scale) {
     };
 }
 
-void focus_camera(RenderState* render_state, CelestialBody* body, Vector3& offset) {
-    Vector3 p = sim_to_render(body->position, render_state->distance_scale);
-    render_state->camera.position = (Vector3){ p.x, p.y + offset.y, p.z + offset.z};
-    render_state->camera.target = p;
-}
+
 
 // Scale a radius for rendering (with minimum visible size)
 float scale_radius(double radius, double scale) {

src/renderer.h

@@ -15,6 +15,7 @@ struct RenderState {
     bool show_body_info;      // Toggle for info panel
     int body_list_scroll;     // Scroll position for body list
     int body_list_active;     // Active item index in body list
+    bool camera_follow_body;  // Whether camera follows selected body
 };
 
 // Renderer initialization and cleanup
@@ -23,8 +24,7 @@ void close_renderer();
 
 // Camera setup and control
 void setup_camera(RenderState* render_state);
-void update_camera(RenderState* render_state);
-void focus_camera(RenderState* render_state, CelestialBody* body, Vector3& offset);
+void update_camera(RenderState* render_state, SimulationState* sim);
 
 // Rendering functions
 void render_body(CelestialBody* body, RenderState* render_state);