ImGuiManager: Fix stutter when multiple OSD messages lapse

src/util/imgui_manager.cpp

@@ -815,9 +815,22 @@ void ImGuiManager::DrawOSDMessages(Common::Timer::Value current_time)
     float actual_y = msg.last_y;
     if (msg.target_y != expected_y)
     {
+      if (msg.last_y < 0.0f)
+      {
+        // First showing.
+        msg.last_y = expected_y;
+      }
+      else
+      {
+        // We got repositioned, probably due to another message above getting removed.
+        const float time_since_move =
+          static_cast<float>(Common::Timer::ConvertValueToSeconds(current_time - msg.move_time));
+        const float frac = Easing::OutExpo(time_since_move / MOVE_DURATION);
+        msg.last_y = std::floor(msg.last_y - ((msg.last_y - msg.target_y) * frac));
+      }
+
       msg.move_time = current_time;
       msg.target_y = expected_y;
-      msg.last_y = (msg.last_y < 0.0f) ? expected_y : msg.last_y;
       actual_y = msg.last_y;
     }
     else if (actual_y != expected_y)
@@ -833,7 +846,7 @@ void ImGuiManager::DrawOSDMessages(Common::Timer::Value current_time)
       else
       {
         const float frac = Easing::OutExpo(time_since_move / MOVE_DURATION);
-        actual_y = msg.last_y - ((msg.last_y - msg.target_y) * frac);
+        actual_y = std::floor(msg.last_y - ((msg.last_y - msg.target_y) * frac));
       }
     }