Use an InputEventSpy to notify about key and modifier state changes

Summary:
Instead of emitting the key state changed and modifier state changed
signals from the right point before processing the events, let's use
an InputEventSpy to do that. The spies were introduced to be called
directly before the event processing. So the contract still holds.

Reviewers: #kwin, #plasma_on_wayland

Subscribers: plasma-devel, kwin

Tags: #plasma_on_wayland, #kwin

Differential Revision: https://phabricator.kde.org/D4128

keyboard_input.cpp

@@ -506,10 +506,64 @@ KeyboardInputRedirection::KeyboardInputRedirection(InputRedirection *parent)
 
 KeyboardInputRedirection::~KeyboardInputRedirection() = default;
 
+class KeyStateChangedSpy : public InputEventSpy
+{
+public:
+    KeyStateChangedSpy(InputRedirection *input)
+        : m_input(input)
+    {
+    }
+
+    void keyEvent(KeyEvent *event) override
+    {
+        if (event->isAutoRepeat()) {
+            return;
+        }
+        emit m_input->keyStateChanged(event->nativeScanCode(), event->type() == QEvent::KeyPress ? InputRedirection::KeyboardKeyPressed : InputRedirection::KeyboardKeyReleased);
+    }
+
+private:
+    InputRedirection *m_input;
+};
+
+class ModifiersChangedSpy : public InputEventSpy
+{
+public:
+    ModifiersChangedSpy(InputRedirection *input)
+        : m_input(input)
+        , m_modifiers()
+    {
+    }
+
+    void keyEvent(KeyEvent *event) override
+    {
+        if (event->isAutoRepeat()) {
+            return;
+        }
+        updateModifiers(event->modifiers());
+    }
+
+    void updateModifiers(Qt::KeyboardModifiers mods)
+    {
+        if (mods == m_modifiers) {
+            return;
+        }
+        emit m_input->keyboardModifiersChanged(mods, m_modifiers);
+        m_modifiers = mods;
+    }
+
+private:
+    InputRedirection *m_input;
+    Qt::KeyboardModifiers m_modifiers;
+};
+
 void KeyboardInputRedirection::init()
 {
     Q_ASSERT(!m_inited);
     m_inited = true;
+    m_input->installInputEventSpy(new KeyStateChangedSpy(m_input));
+    m_modifiersChangedSpy = new ModifiersChangedSpy(m_input);
+    m_input->installInputEventSpy(m_modifiersChangedSpy);
 
     // setup key repeat
     m_keyRepeat.timer = new QTimer(this);
@@ -644,12 +698,7 @@ void KeyboardInputRedirection::processKey(uint32_t key, InputRedirection::Keyboa
     }
 
     if (!autoRepeat) {
-        emit m_input->keyStateChanged(key, state);
-        const Qt::KeyboardModifiers oldMods = modifiers();
         m_xkb->updateKey(key, state);
-        if (oldMods != modifiers()) {
-            emit m_input->keyboardModifiersChanged(modifiers(), oldMods);
-        }
     }
 
     const xkb_keysym_t keySym = m_xkb->currentKeysym();
@@ -686,11 +735,8 @@ void KeyboardInputRedirection::processModifiers(uint32_t modsDepressed, uint32_t
         return;
     }
     // TODO: send to proper Client and also send when active Client changes
-    Qt::KeyboardModifiers oldMods = modifiers();
     m_xkb->updateModifiers(modsDepressed, modsLatched, modsLocked, group);
-    if (oldMods != modifiers()) {
+    m_modifiersChangedSpy->updateModifiers(modifiers());
-        emit m_input->keyboardModifiersChanged(modifiers(), oldMods);
-    }
 }
 
 void KeyboardInputRedirection::processKeymapChange(int fd, uint32_t size)

keyboard_input.h

@@ -43,6 +43,7 @@ namespace KWin
 {
 
 class InputRedirection;
+class ModifiersChangedSpy;
 class Toplevel;
 
 namespace LibInput
@@ -179,6 +180,7 @@ private:
         quint32 time = 0;
         QTimer *timer = nullptr;
     } m_keyRepeat;
+    ModifiersChangedSpy *m_modifiersChangedSpy = nullptr;
 };
 
 inline