Fix raygui body selection - GuiListView return value bug

Issue: GuiListView() always returns 0 (known raygui bug), causing
body selection to never work.

Fix:
- Added body_list_scroll and body_list_active to RenderState for persistence
- Check body_list_active parameter changes instead of return value
- Initialize active state to -1 in main.cpp

Reference: https://github.com/raysan5/raygui/issues/448

src/main.cpp

@@ -40,6 +40,8 @@ void run_gui_simulation(SimulationState* sim) {
     render_state.selected_body_index = -1;  // No selection initially
     render_state.show_body_list = false;
     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
 
     bool paused = false;
     double speed_multiplier = 1.0;

src/renderer.cpp

@@ -402,14 +402,13 @@ void render_body_list_ui(SimulationState* sim, RenderState* render_state) {
         (float)panel_height - 29
     };
 
-    int focus = render_state->selected_body_index; // 0-based indexing
-    if (focus < 0) focus = 0;
+    int previous_active = render_state->body_list_active;
+    GuiListView(list_bounds, body_list_text, &render_state->body_list_scroll, &render_state->body_list_active);
 
-    int active = 0; // Raygui uses this internally
-    int result = GuiListView(list_bounds, body_list_text, &focus, &active);
-
-    if (result >= 0 && result < sim->body_count) {
-        render_state->selected_body_index = result;
+    // Check if a body was selected (active changed from -1 or previous value)
+    if (render_state->body_list_active >= 0 && render_state->body_list_active < sim->body_count &&
+        render_state->body_list_active != previous_active) {
+        render_state->selected_body_index = render_state->body_list_active;
         render_state->show_body_info = true;
     }
 

src/renderer.h

@@ -13,6 +13,8 @@ struct RenderState {
     int selected_body_index;  // -1 = no selection
     bool show_body_list;      // Toggle for list panel
     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
 };
 
 // Renderer initialization and cleanup