Hold Keys mode: keys stay down while touched, like a hardware keyboard

- HardwareKeys presses a key's unshifted keysym on touch and releases it
  on lift, through fake input; held keys repeat and combine as on a
  physical keyboard (games, Shift+click)
- Shift/Ctrl/Alt/Super are plain held keys, caps lock is the system's,
  dead keys compose in the app
- No long-press, flick, trackpad or rollover in this mode; nothing is
  left held when the mode is turned off or touches are cancelled
- Settings switch; default stays the touch (virtual keyboard) mode

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/CMakeLists.txt

@@ -8,6 +8,7 @@ qt_add_library(sloposk_core STATIC
     input/ShiftState.h input/ShiftState.cpp
     input/Modifiers.h input/Modifiers.cpp
     input/DeadKeys.h input/DeadKeys.cpp
+    input/HardwareKeys.h input/HardwareKeys.cpp
     input/PointerTracker.h input/PointerTracker.cpp
     input/AlternatesPicker.h input/AlternatesPicker.cpp
     input/KeyRepeater.h input/KeyRepeater.cpp

src/backend/KWinFakeInput.cpp

@@ -53,6 +53,12 @@ void KWinFakeInput::sendKeysym(quint32 keysym, Qt::KeyboardModifiers modifiers)
     }
 }
 
+void KWinFakeInput::setKeyPressed(quint32 keysym, bool pressed)
+{
+    if (isActive())
+        keyboard_keysym(keysym, pressed ? Pressed : Released);
+}
+
 void KWinFakeInput::typeText(const QString &text)
 {
     for (const char32_t ucs : text.toUcs4())

src/backend/KWinFakeInput.h

@@ -19,6 +19,9 @@ public:
     // Presses and releases `keysym` with `modifiers` held. KWin finds the key
     // (and any shift level) in the current keymap.
     void sendKeysym(quint32 keysym, Qt::KeyboardModifiers modifiers = Qt::NoModifier);
+    // Presses or releases one key, for keys held as long as the finger is
+    // down. Modifiers are keysyms too (Shift_L...): KWin holds the real key.
+    void setKeyPressed(quint32 keysym, bool pressed);
     // Types each character as its keysym.
     void typeText(const QString &text);
 };

src/backend/KWinInputMethod.cpp

@@ -78,6 +78,13 @@ void KWinInputMethod::sendKeysym(quint32 keysym, Qt::KeyboardModifiers modifiers
         m_fakeInput.sendKeysym(keysym, modifiers);
 }
 
+// Always fake input, even in a text field: held keys are key events, and the
+// input method's keysyms can't hold a modifier across keys.
+void KWinInputMethod::setKeyPressed(quint32 keysym, bool pressed)
+{
+    m_fakeInput.setKeyPressed(keysym, pressed);
+}
+
 void KWinInputMethod::activate(::zwp_input_method_context_v1 *context)
 {
     m_context = std::make_unique<KWinInputContext>(context);

src/backend/KWinInputMethod.h

@@ -50,6 +50,7 @@ public:
     void replaceBeforeCursor(const QString &before, const QString &text) override;
     void setPreedit(const QString &text) override;
     void sendKeysym(quint32 keysym, Qt::KeyboardModifiers modifiers) override;
+    void setKeyPressed(quint32 keysym, bool pressed) override;
 
 Q_SIGNALS:
     void availableChanged();

src/backend/TextBackend.h

@@ -29,6 +29,9 @@ public:
     virtual void replaceBeforeCursor(const QString &before, const QString &text) = 0;
     Q_INVOKABLE virtual void setPreedit(const QString &text) = 0;
     Q_INVOKABLE virtual void sendKeysym(quint32 keysym, Qt::KeyboardModifiers modifiers = Qt::NoModifier) = 0;
+    // Presses or releases one key, held in between like a hardware key, to
+    // the focused window. Modifiers are keys too (Shift_L, Control_L...).
+    virtual void setKeyPressed(quint32 keysym, bool pressed) = 0;
 
 Q_SIGNALS:
     void activeChanged();

src/engine/DirectEngine.cpp

@@ -21,3 +21,8 @@ void DirectEngine::sendKeysym(quint32 keysym, Qt::KeyboardModifiers modifiers)
 {
     m_backend.sendKeysym(keysym, modifiers);
 }
+
+void DirectEngine::setKeyPressed(quint32 keysym, bool pressed)
+{
+    m_backend.setKeyPressed(keysym, pressed);
+}

src/engine/DirectEngine.h

@@ -12,6 +12,7 @@ public:
     void commitText(const QString &text) override;
     void replaceBeforeCursor(const QString &before, const QString &text) override;
     void sendKeysym(quint32 keysym, Qt::KeyboardModifiers modifiers) override;
+    void setKeyPressed(quint32 keysym, bool pressed) override;
 
 private:
     TextBackend &m_backend;

src/engine/InputEngine.h

@@ -15,4 +15,6 @@ public:
     // See TextBackend::replaceBeforeCursor.
     virtual void replaceBeforeCursor(const QString &before, const QString &text) = 0;
     virtual void sendKeysym(quint32 keysym, Qt::KeyboardModifiers modifiers = Qt::NoModifier) = 0;
+    // See TextBackend::setKeyPressed.
+    virtual void setKeyPressed(quint32 keysym, bool pressed) = 0;
 };

src/input/HardwareKeys.cpp

@@ -0,0 +1,98 @@
+#include "HardwareKeys.h"
+
+#include "engine/InputEngine.h"
+
+#include <xkbcommon/xkbcommon.h>
+
+namespace {
+
+quint32 modifierKeysym(const QString &name)
+{
+    if (name == u"ctrl")
+        return XKB_KEY_Control_L;
+    if (name == u"alt")
+        return XKB_KEY_Alt_L;
+    return XKB_KEY_Super_L;
+}
+
+} // namespace
+
+HardwareKeys::HardwareKeys(InputEngine &engine)
+    : m_engine(engine)
+{
+}
+
+bool HardwareKeys::handles(const KeyDef &key)
+{
+    return keysymOf(key) != XKB_KEY_NoSymbol;
+}
+
+// The key's unshifted symbol: a held Shift (or caps lock) makes the app pick
+// the shifted one, as with a hardware key.
+quint32 HardwareKeys::keysymOf(const KeyDef &key)
+{
+    switch (key.type) {
+    case KeyType::Character:
+        return key.dead ? key.dead : xkb_utf32_to_keysym(key.label.toUcs4().value(0));
+    case KeyType::Space: return XKB_KEY_space;
+    case KeyType::Backspace: return XKB_KEY_BackSpace;
+    case KeyType::Enter: return XKB_KEY_Return;
+    case KeyType::Shift: return XKB_KEY_Shift_L;
+    case KeyType::CapsLock: return XKB_KEY_Caps_Lock;
+    case KeyType::Modifier: return modifierKeysym(key.modifier);
+    case KeyType::Keysym: return key.keysym;
+    default: return XKB_KEY_NoSymbol;
+    }
+}
+
+void HardwareKeys::press(const KeyDef &key)
+{
+    const quint32 keysym = keysymOf(key);
+    if (keysym == XKB_KEY_NoSymbol)
+        return;
+    if (m_down[keysym]++ == 0)
+        m_engine.setKeyPressed(keysym, true);
+    if (key.type == KeyType::CapsLock)
+        m_capsLock = !m_capsLock;
+}
+
+void HardwareKeys::release(const KeyDef &key)
+{
+    const quint32 keysym = keysymOf(key);
+    const auto it = m_down.find(keysym);
+    if (it == m_down.end())
+        return;
+    if (--*it == 0) {
+        m_down.erase(it);
+        m_engine.setKeyPressed(keysym, false);
+    }
+}
+
+void HardwareKeys::releaseAll()
+{
+    for (auto it = m_down.cbegin(); it != m_down.cend(); ++it)
+        m_engine.setKeyPressed(it.key(), false);
+    m_down.clear();
+}
+
+bool HardwareKeys::isShiftHeld() const
+{
+    return m_down.contains(XKB_KEY_Shift_L);
+}
+
+ShiftLevel HardwareKeys::shiftLevel() const
+{
+    if (isShiftHeld())
+        return ShiftLevel::Shifted;
+    return m_capsLock ? ShiftLevel::Capitals : ShiftLevel::None;
+}
+
+QVariantMap HardwareKeys::modifierModes() const
+{
+    QVariantMap modes;
+    for (const char *name : {"ctrl", "alt", "super"}) {
+        const QString key = QString::fromLatin1(name);
+        modes.insert(key, m_down.contains(modifierKeysym(key)) ? 1 : 0);
+    }
+    return modes;
+}

src/input/HardwareKeys.h

@@ -0,0 +1,41 @@
+#pragma once
+
+#include "layout/Layout.h"
+
+#include <QHash>
+#include <QVariantMap>
+
+class InputEngine;
+
+// The "hold keys" mode: the keyboard acts like a hardware one. A key is down
+// while the finger is, so apps see held keys (games, Shift+click, the
+// system's key repeat). Shift, Ctrl, Alt and Super are plain keys, caps lock
+// is the system's, and dead keys compose in the app; none of the touch
+// conveniences (sticky shift, auto-capitalization, accents) apply.
+class HardwareKeys
+{
+public:
+    explicit HardwareKeys(InputEngine &engine);
+
+    // True if `key` is one this mode presses (not a layer, globe or dismiss key).
+    static bool handles(const KeyDef &key);
+
+    void press(const KeyDef &key);
+    void release(const KeyDef &key);
+    // Lets go of everything still down, e.g. when the mode is turned off.
+    void releaseAll();
+
+    // For the view: shift shown while held, caps lock while on.
+    ShiftLevel shiftLevel() const;
+    bool isShiftHeld() const;
+    bool isCapsLockOn() const { return m_capsLock; }
+    // "ctrl"/"alt"/"super" → 1 while held (ShiftState::Mode::Once), else 0.
+    QVariantMap modifierModes() const;
+
+private:
+    static quint32 keysymOf(const KeyDef &key);
+
+    InputEngine &m_engine;
+    QHash<quint32, int> m_down; // keysym → fingers holding it
+    bool m_capsLock = false;
+};

src/input/KeyboardController.cpp

@@ -22,6 +22,7 @@ KeyboardController::KeyboardController(InputEngine &engine, LayoutModel &model,
     : QObject(parent)
     , m_engine(engine)
     , m_model(model)
+    , m_hardware(engine)
     , m_keysymRepeater(KeysymRepeat)
 {
     connect(&m_backspaceRepeater, &KeyRepeater::repeat, this, &KeyboardController::deleteBackward);
@@ -30,11 +31,34 @@ KeyboardController::KeyboardController(InputEngine &engine, LayoutModel &model,
 
 KeyboardController::ShiftMode KeyboardController::shiftMode() const
 {
+    if (m_options.holdKeys) {
+        if (m_hardware.isCapsLockOn())
+            return ShiftMode::Locked;
+        return m_hardware.isShiftHeld() ? ShiftMode::Once : ShiftMode::Off;
+    }
     return ShiftMode(m_shift.mode());
 }
 
+QVariantMap KeyboardController::modifierModes() const
+{
+    return m_options.holdKeys ? m_hardware.modifierModes() : m_modifiers.modes();
+}
+
+bool KeyboardController::holdKey(const KeyDef &key, bool pressed)
+{
+    if (!m_options.holdKeys || !HardwareKeys::handles(key))
+        return false;
+    pressed ? m_hardware.press(key) : m_hardware.release(key);
+    m_model.setShiftLevel(shiftLevel());
+    Q_EMIT shiftChanged();
+    Q_EMIT modifiersChanged();
+    return true;
+}
+
 void KeyboardController::keyDown(const KeyDef &key, qint64 timeMs)
 {
+    if (holdKey(key, true))
+        return;
     switch (key.type) {
     case KeyType::Shift:
         changeShift([&] { m_shift.press(timeMs); });
@@ -72,6 +96,8 @@ void KeyboardController::keyDown(const KeyDef &key, qint64 timeMs)
 
 void KeyboardController::keyUp(const KeyDef &key, KeyOutput output, const QString &alternate, qint64)
 {
+    if (holdKey(key, false))
+        return;
     switch (key.type) {
     case KeyType::Shift:
         changeShift([&] { m_shift.release(); });
@@ -112,6 +138,8 @@ void KeyboardController::keyUp(const KeyDef &key, KeyOutput output, const QStrin
 
 void KeyboardController::keyCancelled(const KeyDef &key)
 {
+    if (holdKey(key, false))
+        return;
     if (key.type == KeyType::Shift)
         changeShift([&] { m_shift.release(); });
     else if (key.type == KeyType::Modifier) {
@@ -125,6 +153,7 @@ void KeyboardController::keyCancelled(const KeyDef &key)
 
 void KeyboardController::slideReleased(const KeyDef &target, qint64 timeMs)
 {
+    holdKey(target, true); // only in hold-keys mode: the slide never pressed it
     keyUp(target, KeyOutput::Primary, {}, timeMs);
     m_model.setLayer(m_layerBeforeSwitch);
 }
@@ -158,7 +187,12 @@ void KeyboardController::setContext(const TextContext &context)
 
 void KeyboardController::setOptions(const TypingOptions &options)
 {
+    if (m_options.holdKeys && !options.holdKeys)
+        m_hardware.releaseAll();
     m_options = options;
+    m_model.setShiftLevel(shiftLevel());
+    Q_EMIT shiftChanged();
+    Q_EMIT modifiersChanged();
     autoCapitalize();
 }
 
@@ -254,6 +288,8 @@ void KeyboardController::autoCapitalize()
 
 ShiftLevel KeyboardController::shiftLevel() const
 {
+    if (m_options.holdKeys)
+        return m_hardware.shiftLevel();
     if (m_shift.appliesToShortcuts())
         return ShiftLevel::Shifted;
     return m_shift.isActive() ? ShiftLevel::Capitals : ShiftLevel::None;

src/input/KeyboardController.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "DeadKeys.h"
+#include "HardwareKeys.h"
 #include "KeyRepeater.h"
 #include "Modifiers.h"
 #include "ShiftState.h"
@@ -43,7 +44,9 @@ public:
     KeyboardController(InputEngine &engine, LayoutModel &model, QObject *parent = nullptr);
 
     ShiftMode shiftMode() const;
-    QVariantMap modifierModes() const { return m_modifiers.modes(); }
+    QVariantMap modifierModes() const;
+    // Hold-keys mode: no long-press, flick or trackpad gestures, no rollover.
+    bool holdsKeys() const { return m_options.holdKeys; }
 
     void keyDown(const KeyDef &key, qint64 timeMs);
     void keyUp(const KeyDef &key, KeyOutput output, const QString &alternate, qint64 timeMs);
@@ -73,6 +76,8 @@ private:
     void sendKey(quint32 keysym);
     Qt::KeyboardModifiers shortcutModifiers() const;
     ShiftLevel shiftLevel() const;
+    // Hold-keys mode: forwards the key to m_hardware; false if it isn't one it presses.
+    bool holdKey(const KeyDef &key, bool pressed);
     void useModifiers();
     void deleteBackward(bool wholeWord);
     void sendRepeatedKeysym();
@@ -86,6 +91,7 @@ private:
     TypingOptions m_options;
     ShiftState m_shift;
     Modifiers m_modifiers;
+    HardwareKeys m_hardware;
     DeadKeys m_deadKeys;
     KeyRepeater m_backspaceRepeater;
     KeyRepeater m_keysymRepeater; // arrows, Delete, ...

src/input/KeyboardSurface.cpp

@@ -99,7 +99,9 @@ void KeyboardSurface::pointerDown(int id, QPointF pos, qint64 timeMs)
 {
     if (!m_model || !m_controller)
         return;
-    commitPendingTaps(timeMs);
+    // Rollover would let go of keys still held, which hold-keys mode must not.
+    if (!m_controller->holdsKeys())
+        commitPendingTaps(timeMs);
 
     const int index = m_model->keyAt(pos);
     if (index < 0)
@@ -107,6 +109,7 @@ void KeyboardSurface::pointerDown(int id, QPointF pos, qint64 timeMs)
 
     PointerTracker::Config config;
     config.flickDistance = m_model->keyRect(index).height() * FlickDistanceRatio;
+    config.gestures = !m_controller->holdsKeys();
     const Pointer pointer{PointerTracker(m_model->key(index), pos, config), index, -1, m_nextSerial++};
     m_pointers.insert(id, pointer);
     m_model->setPressed(index, true);

src/input/PointerTracker.cpp

@@ -12,7 +12,7 @@ PointerTracker::PointerTracker(const KeyDef &key, QPointF start, Config config)
 
 bool PointerTracker::wantsLongPress() const
 {
-    return m_key.type == KeyType::Space || !m_key.alternates.isEmpty();
+    return m_config.gestures && (m_key.type == KeyType::Space || !m_key.alternates.isEmpty());
 }
 
 void PointerTracker::moveTo(QPointF pos)
@@ -28,13 +28,13 @@ void PointerTracker::moveTo(QPointF pos)
 
     if (m_key.type == KeyType::LayerSwitch)
         m_gesture = Gesture::Slide;
-    else if (!m_key.flick.isEmpty() && delta.y() > qAbs(delta.x()))
+    else if (m_config.gestures && !m_key.flick.isEmpty() && delta.y() > qAbs(delta.x()))
         m_gesture = Gesture::Flick;
 }
 
 bool PointerTracker::longPressElapsed()
 {
-    if (m_gesture != Gesture::Tap || m_moved)
+    if (!m_config.gestures || m_gesture != Gesture::Tap || m_moved)
         return false;
 
     if (m_key.type == KeyType::Space) {

src/input/PointerTracker.h

@@ -24,6 +24,7 @@ public:
         int longPressMs = 450;
         qreal trackpadStep = 14;  // horizontal travel per cursor step
         qreal trackpadRowStep = 40; // vertical travel per line
+        bool gestures = true;     // false: only taps and layer slides (hold-keys mode)
     };
 
     PointerTracker(const KeyDef &key, QPointF start, Config config);

src/input/TypingOptions.h

@@ -5,6 +5,7 @@
 struct TypingOptions {
     bool autoCapitalize = true;
     bool doubleSpacePeriod = true;
+    bool holdKeys = false; // keys stay down while touched, like a hardware keyboard (see HardwareKeys)
 
     bool operator==(const TypingOptions &) const = default;
 };

src/settings/Settings.cpp

@@ -7,6 +7,7 @@
 namespace {
 constexpr auto AutoCapitalizeKey = "typing/autoCapitalize";
 constexpr auto DoubleSpacePeriodKey = "typing/doubleSpacePeriod";
+constexpr auto HoldKeysKey = "typing/holdKeys";
 constexpr auto VisibleSectionsKey = "layout/visibleSections";
 constexpr auto FullKeyboardKey = "layout/fullKeyboard";
 constexpr auto AlwaysVisibleKey = "window/alwaysVisible";
@@ -19,6 +20,7 @@ Settings::Settings(QObject *parent)
     const TypingOptions defaults;
     m_typing.autoCapitalize = store.value(AutoCapitalizeKey, defaults.autoCapitalize).toBool();
     m_typing.doubleSpacePeriod = store.value(DoubleSpacePeriodKey, defaults.doubleSpacePeriod).toBool();
+    m_typing.holdKeys = store.value(HoldKeysKey, defaults.holdKeys).toBool();
     m_visibleSections = store.value(VisibleSectionsKey, QStringList{MainSectionId}).toStringList();
     if (m_visibleSections.isEmpty())
         m_visibleSections = {MainSectionId};
@@ -72,6 +74,13 @@ void Settings::setDoubleSpacePeriod(bool enabled)
     setTypingOptions(options);
 }
 
+void Settings::setHoldKeys(bool enabled)
+{
+    TypingOptions options = m_typing;
+    options.holdKeys = enabled;
+    setTypingOptions(options);
+}
+
 void Settings::setTypingOptions(const TypingOptions &options)
 {
     if (options == m_typing)
@@ -80,5 +89,6 @@ void Settings::setTypingOptions(const TypingOptions &options)
     QSettings store;
     store.setValue(AutoCapitalizeKey, m_typing.autoCapitalize);
     store.setValue(DoubleSpacePeriodKey, m_typing.doubleSpacePeriod);
+    store.setValue(HoldKeysKey, m_typing.holdKeys);
     Q_EMIT typingOptionsChanged();
 }

src/settings/Settings.h

@@ -15,6 +15,7 @@ class Settings : public QObject
     QML_UNCREATABLE("Created in C++")
     Q_PROPERTY(bool autoCapitalize READ autoCapitalize WRITE setAutoCapitalize NOTIFY typingOptionsChanged)
     Q_PROPERTY(bool doubleSpacePeriod READ doubleSpacePeriod WRITE setDoubleSpacePeriod NOTIFY typingOptionsChanged)
+    Q_PROPERTY(bool holdKeys READ holdKeys WRITE setHoldKeys NOTIFY typingOptionsChanged)
     // Which key blocks are shown: "main" (the typing keys) and template section ids.
     Q_PROPERTY(QStringList visibleSections READ visibleSections NOTIFY visibleSectionsChanged)
     // iPad Pro-style full keyboard (number row, tab, ctrl/alt/super) instead of the compact one.
@@ -31,6 +32,8 @@ public:
     void setAutoCapitalize(bool enabled);
     bool doubleSpacePeriod() const { return m_typing.doubleSpacePeriod; }
     void setDoubleSpacePeriod(bool enabled);
+    bool holdKeys() const { return m_typing.holdKeys; }
+    void setHoldKeys(bool enabled);
 
     QStringList visibleSections() const { return m_visibleSections; }
     // Hiding the last visible section is refused: something must stay on screen.