fix stroke preview priority

src/util.h

@@ -153,7 +153,7 @@ template<typename T, int Max = 0>
 class BlockingQueue
 {
 public:
-    std::deque<T> q;
+    std::deque<std::pair<T, bool>> q;
     std::condition_variable post_cv;
     std::condition_variable get_cv;
     mutable std::mutex mutex;
@@ -171,7 +171,7 @@ public:
             post_cv.wait(lock, [&]() { return unlocked | (q.size() < Max); });
             if (q.size() >= Max) return;
         }
-        q.push_back(pkt);
+        q.push_back({ pkt, false });
         get_cv.notify_one();
     }
     void PostUnique(T pkt, bool top)
@@ -182,8 +182,20 @@ public:
             post_cv.wait(lock, [&]() { return unlocked | (q.size() < Max); });
             if (q.size() >= Max) return;
         }
-        if (std::find(q.begin(), q.end(), pkt) == q.end())
-            top ? q.push_front(pkt) : q.push_back(pkt);
+        auto search = std::make_pair(pkt, top);
+        if (std::find(q.begin(), q.end(), search) == q.end())
+        {
+            if (top)
+            {
+                // find the first low priority
+                auto low = std::find_if(q.begin(), q.end(), [](auto const& x) { return x.second == false; });
+                q.insert(low, { pkt, top });
+            }
+            else
+            {
+                q.push_back({ pkt, top });
+            }
+        }
         get_cv.notify_one();
     }
     T Get()
@@ -193,10 +205,10 @@ public:
         get_cv.wait(lock, [&]() { return unlocked | (q.size() > 0); });
         if (q.empty())
             return std::move(emptyT);
-        T tmp = std::move(q.front());
+        auto tmp = std::move(q.front());
         q.pop_front();
         if (Max > 0) post_cv.notify_all();
-        return std::move(tmp);
+        return std::move(tmp.first);
     }
     void UnlockGetters()
     {