Reuse same ID when reconnecting monitor, otherwise use minimum available ID (#2666)

Fixes #2601

3 files changed, 20 insertions, 8 deletions

diff --git a/src/Compositor.cpp b/src/Compositor.cpp
index ae3ef109..50ea0b5d 100644
--- a/src/Compositor.cpp
+++ b/src/Compositor.cpp
@@ -1,6 +1,7 @@
 #include "Compositor.hpp"
 #include "helpers/Splashes.hpp"
 #include <random>
+#include <unordered_set>
 #include "debug/HyprCtl.hpp"
 #include "debug/CrashReporter.hpp"
 #ifdef USES_SYSTEMD
@@ -1697,14 +1698,23 @@ void CCompositor::updateWindowAnimatedDecorationValues(CWindow* pWindow) {
         d->updateWindow(pWindow);
 }
 
-int CCompositor::getNextAvailableMonitorID() {
-    int64_t topID = -1;
-    for (auto& m : m_vRealMonitors) {
-        if ((int64_t)m->ID > topID)
-            topID = m->ID;
+int CCompositor::getNextAvailableMonitorID(std::string const& name) {
+    // reuse ID if it's already in the map
+    if (m_mMonitorIDMap.contains(name))
+        return m_mMonitorIDMap[name];
+
+    // otherwise, find minimum available ID that is not in the map
+    std::unordered_set<int> usedIDs;
+    for (auto const& monitor : m_vRealMonitors) {
+        usedIDs.insert(monitor->ID);
     }
 
-    return topID + 1;
+    int nextID = 0;
+    while (usedIDs.count(nextID) > 0) {
+        nextID++;
+    }
+    m_mMonitorIDMap[name] = nextID;
+    return nextID;
 }
 
 void CCompositor::swapActiveWorkspaces(CMonitor* pMonitorA, CMonitor* pMonitorB) {
diff --git a/src/Compositor.hpp b/src/Compositor.hpp
index 6f1be1b6..e4f5483f 100644
--- a/src/Compositor.hpp
+++ b/src/Compositor.hpp
@@ -101,6 +101,8 @@ class CCompositor {
     std::vector<CWindow*>                     m_vWindowsFadingOut;
     std::vector<SLayerSurface*>               m_vSurfacesFadingOut;
 
+    std::unordered_map<std::string, int64_t>  m_mMonitorIDMap;
+
     void                                      initServer();
     void                                      startCompositor();
     void                                      cleanup();
@@ -168,7 +170,7 @@ class CCompositor {
     CMonitor*      getMonitorInDirection(const char&);
     void           updateAllWindowsAnimatedDecorationValues();
     void           updateWindowAnimatedDecorationValues(CWindow*);
-    int            getNextAvailableMonitorID();
+    int            getNextAvailableMonitorID(std::string const & name);
     void           moveWorkspaceToMonitor(CWorkspace*, CMonitor*);
     void           swapActiveWorkspaces(CMonitor*, CMonitor*);
     CMonitor*      getMonitorFromString(const std::string&);
diff --git a/src/events/Monitors.cpp b/src/events/Monitors.cpp
index 6455d4df..73f5a6f6 100644
--- a/src/events/Monitors.cpp
+++ b/src/events/Monitors.cpp
@@ -76,7 +76,7 @@ void Events::listener_newOutput(wl_listener* listener, void* data) {
         Debug::log(LOG, "Adding completely new monitor.");
         PNEWMONITORWRAP = &g_pCompositor->m_vRealMonitors.emplace_back(std::make_shared<CMonitor>());
 
-        (*PNEWMONITORWRAP)->ID = g_pCompositor->getNextAvailableMonitorID();
+        (*PNEWMONITORWRAP)->ID = g_pCompositor->getNextAvailableMonitorID(OUTPUT->name);
     }
 
     const auto PNEWMONITOR = PNEWMONITORWRAP->get();