[Input] Add last used controller tracker

src/xenia/hid/input_system.cc

@@ -100,6 +100,10 @@ X_RESULT InputSystem::GetState(uint32_t user_index, X_INPUT_STATE* out_state) {
     if (result == X_ERROR_SUCCESS) {
       UpdateUsedSlot(driver.get(), user_index, any_connected);
       AdjustDeadzoneLevels(user_index, &out_state->gamepad);
+
+      if (out_state->gamepad.buttons != 0) {
+        last_used_slot = user_index;
+      }
       return result;
     }
   }

src/xenia/hid/input_system.h

@@ -53,6 +53,8 @@ class InputSystem {
     return connected_slots;
   }
 
+  uint32_t GetLastUsedSlot() const { return last_used_slot; }
+
   std::unique_lock<xe_unlikely_mutex> lock();
 
  private:
@@ -73,6 +75,7 @@ class InputSystem {
   std::bitset<XUserMaxUserCount> connected_slots = {};
   std::array<std::pair<joystick_value, joystick_value>, XUserMaxUserCount>
       controllers_max_joystick_value = {};
+  uint32_t last_used_slot = 0;
 
   xe_unlikely_mutex lock_;
 };