perf(core): cache cursor output and emit it on change

src/core/lockscreen.cpp

@@ -14,11 +14,10 @@
 
 #ifdef EXT_SESSION_LOCK_V1
 #include "rootsurfacecontainer.h"
 #include "surfacewrapper.h"
 
-#include <wcursor.h>
 #include <wsessionlock.h>
 #include <wsessionlocksurface.h>
 #endif
 
 WAYLIB_SERVER_USE_NAMESPACE
@@ -37,12 +36,13 @@
 
     // The global login view is lazily created when this container becomes
     // visible (locked) and destroyed when it hides (unlocked). Track the
-    // cursor so the login UI follows the output the mouse is on.
+    // output under the cursor so the login UI follows the mouse without
+    // recomputing the output on every cursor motion.
     connect(this, &QQuickItem::visibleChanged, this, &LockScreen::onLoginViewVisibleChanged);
-    connect(rootContainer()->cursor(),
-            &WCursor::positionChanged,
+    connect(rootContainer(),
+            &RootSurfaceContainer::cursorOutputChanged,
             this,
-            &LockScreen::onCursorPositionChanged);
+            &LockScreen::repositionLoginView);
 }
 
 void LockScreen::lock()
@@ -243,13 +243,6 @@
     m_loginView->setWidth(size.width());
     m_loginView->setHeight(size.height());
 }
-
-void LockScreen::onCursorPositionChanged()
-{
-    if (m_loginView) {
-        repositionLoginView();
-    }
-}
 #if EXT_SESSION_LOCK_V1
 // ext_session_lock_v1 capabilities
 

src/core/lockscreen.h

@@ -80,7 +80,6 @@ private Q_SLOTS:
     void createLoginView();
     void destroyLoginView();
     void repositionLoginView();
-    void onCursorPositionChanged();
     Output *followerOutput() const;
 
     ILockScreen *m_impl{ nullptr };

src/core/rootsurfacecontainer.cpp

@@ -86,6 +86,9 @@ void RootSurfaceContainer::init(WServer *server)
             output->updatePositionFromLayout();
         }
         ensureCursorVisible();
+        // The layout may have moved/removed the output under the cursor, so
+        // refresh the cache even without a cursor motion event.
+        updateCursorOutput();
 
         // for (auto s : m_surfaceContainer->surfaces()) {
         //     ensureSurfaceNormalPositionValid(s);
@@ -101,6 +104,7 @@ void RootSurfaceContainer::init(WServer *server)
 
     QObject::connect(m_cursor, &WCursor::positionChanged, this, [this] {
         m_dragSurfaceItem->setPosition(m_cursor->position());
+        updateCursorOutput();
     });
 
     QObject::connect(m_cursor, &WCursor::requestedDragSurfaceChanged, this, [this] {
@@ -387,7 +391,17 @@ WCursor *RootSurfaceContainer::cursor() const
 Output *RootSurfaceContainer::cursorOutput() const
 {
     Q_ASSERT(m_cursor->layout() == m_outputLayout);
-    return outputAt(m_cursor->position());
+    return m_cursorOutput;
+}
+
+void RootSurfaceContainer::updateCursorOutput()
+{
+    Output *output = outputAt(m_cursor->position());
+    if (output == m_cursorOutput)
+        return;
+
+    m_cursorOutput = output;
+    Q_EMIT cursorOutputChanged(output);
 }
 
 Output *RootSurfaceContainer::outputAt(const QPointF &pos) const

src/core/rootsurfacecontainer.h

@@ -121,6 +121,7 @@ public Q_SLOTS:
 
 Q_SIGNALS:
     void primaryOutputChanged();
+    void cursorOutputChanged(Output *output);
     void moveResizeFinised(SurfaceWrapper *surface);
 
 private:
@@ -138,6 +139,7 @@ public Q_SLOTS:
                                   [[maybe_unused]] SurfaceWrapper::State oldState) override;
 
     void ensureCursorVisible();
+    void updateCursorOutput();
     void updateSurfaceOutputs(SurfaceWrapper *surface);
     QQuickItem *ensureEdgeTilePreview();
     void onSeatAdded(WSeat *seat);
@@ -150,6 +152,7 @@ public Q_SLOTS:
     std::unique_ptr<WAYLIB_SERVER_NAMESPACE::WListenerOwner> m_outputLayoutListenerOwner;
     OutputListModel *m_outputModel = nullptr;
     QPointer<Output> m_primaryOutput;
+    QPointer<Output> m_cursorOutput;
     WCursor *m_cursor = nullptr;
     WSurfaceItem *m_dragSurfaceItem = nullptr;
     QPointer<QQuickItem> m_edgeTilePreview;