Add key-held behaviour

This patch introduces a popup window that appears when you
press and hold down an alphabetic key offering diacritics
that can be selected by then pressing a number.

src/CMakeLists.txt

 add_subdirectory(platformtheme)
+add_subdirectory(platforminputcontextplugin)

src/platforminputcontextplugin/CMakeLists.txt

+get_target_property(PLUGIN_DIR Qt5::Gui IMPORTED_LOCATION_UNUSED)
+
+# keyholdmanager has a ton of definitions where
+# needing explicit qstringliteral would negatively affect
+# code readability
+remove_definitions(-DQT_NO_CAST_FROM_ASCII)
+
+add_library(input_plugin MODULE
+    main.cpp
+    plasmaimcontext.cpp
+)
+
+target_link_libraries(input_plugin
+    Qt5::Core
+    Qt5::Gui
+    Qt5::Quick
+    Qt5::Widgets
+    Qt5::GuiPrivate
+    KF5::ConfigCore
+)
+set_target_properties(input_plugin PROPERTIES OUTPUT_NAME plasmaimplatforminputcontextplugin)
+
+install(TARGETS input_plugin LIBRARY DESTINATION ${KDE_INSTALL_QTPLUGINDIR}/platforminputcontexts)
+
+install(DIRECTORY data/ DESTINATION ${KDE_INSTALL_INCLUDEDIR}/PlasmaKeyData)
+configure_file(plasma-key-data.pc.in plasma-key-data.pc @ONLY)
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/plasma-key-data.pc DESTINATION ${KDE_INSTALL_LIBDIR}/pkgconfig)

src/platforminputcontextplugin/data/plasmakeydata.h

+/*
+ *  Copyright 2020 Carson Black <uhhadd@gmail.com>
+ *
+ *  This library is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU Lesser General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License or ( at
+ *  your option ) version 3 or, at the discretion of KDE e.V. ( which shall
+ *  act as a proxy as in section 14 of the GPLv3 ), any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Library General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public License
+ *  along with this library; see the file COPYING.LIB.  If not, write to
+ *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ *  Boston, MA 02110-1301, USA.
+ */
+
+#include <QString>
+#include <QMap>
+#include <QList>
+
+// Curating key data
+// =================
+//
+// There are two main goals with key data here:
+// - to allow users to input letters related to but not in their keyboard language (e.g. Persian glyphs on top of the Arabic set)
+// - to allow users to input useful symbols, such as proper arithmetic symbols and various dashes
+//
+// The former generally is used for letters, while the latter is generally used for punctuation and numbers
+//
+// Latin Letters:
+//
+// Generally, these are going to be diacritics (a + ` = à) or diagraphs (a + e = æ).
+// Letters should be roughly ordered first by amount of speakers of languages that use them,
+// and then by commonality in languages as a secondary factor. For example, the character å is
+// found mostly in northern Germanic languages, which don't have nearly as many speakers as
+// romance languages such as Spanish, which has á. For this reason, á should be ordered before å.
+// Rinse and repeat this process until all the variants you want to offer are well placed.
+//
+// Cyrilic Letters:
+//
+// The same principles as Latin letters apply here. For example, the character ҝ (Ka with a vertical stroke; Azerbaijani)
+// is found in a much less common language than қ (Ka with a descender; many languages found in former Soviet Union territories)
+// so it should be placed after қ in the list of options for к (Ka; lot of languages)
+//
+// Arabic characters:
+//
+// Same deal as Latin and Cyrilic, except now it's going to render poorly in your text editors.
+// Most of these characters only have one alternate form, mostly to add some extra diacritics
+// in order to use a less common form or a form not found in Arabic, e.g. Persian پ from Arabic ب.
+// Alef is a special case here, as it has a lot of "variants" in common use. For example, there's the
+// alef with a hamza sitting on it (ا + ʾ = أ) or a hamza sitting below it (إ). These can be inputted
+// as diagraphs on keyboards, but can also be represented as a held-key variant of alef for input purposes.
+//
+// Hebrew characters:
+//
+// The characters here are the iffiest of the selection, since most don't add anything new to input, just a
+// "convenience" way for inputting characters with a ׳ added, when you can already type it without extra modifiers.
+// However, we're still having them there since they're a logical "variant" of the characters they're for.
+//
+// On the other hand, the ײַ ײ ױ װ work as held keys to offer a meaningful alternative to other methods of inputting
+// them, since these typically require the usage of AltGr to input on most Hebrew keyboards.
+//
+// Numbers:
+//
+// These are mostly exponents and fractions. Their ordering should be self explanatory.
+//
+// Symbols:
+//
+// These are mostly things that look like the key being held, with the exception
+// of ^ being used for directional arrows.
+//
+
+namespace KeyData {
+
+const QMap<QString,QList<QString>> KeyMappings = {
+    //
+    // Latin
+    //
+    {"a", {"à", "á", "â", "ä", "æ", "ã", "å", "ā"}},
+    {"c", {"ç", "ć", "č"}},
+    {"d", {"ð"}},
+    {"e", {"è", "é", "ê", "ë", "ē", "ė", "ę", "ə"}},
+    {"i", {"î", "ï", "í", "ī", "į", "ì"}},
+    {"l", {"ł"}},
+    {"n", {"ñ", "ń"}},
+    {"o", {"ô", "ö", "ò", "ó", "œ", "ø", "ō", "õ"}},
+    {"s", {"ß", "ś", "š"}},
+    {"u", {"û", "ü", "ù", "ú", "ū"}},
+    {"x", {"×"}},
+    {"y", {"ÿ", "ұ", "ү", "ӯ", "ў"}},
+    {"z", {"ž", "ź", "ż"}},
+    //
+    // Cyrilic
+    //
+    {"г", {"ғ"}},
+    {"е", {"ё"}}, // this in fact NOT the same E as before
+    {"и", {"ӣ", "і"}}, // і is not i
+    {"й", {"ј"}}, // ј is not j
+    {"к", {"қ", "ҝ",}},
+    {"н", {"ң", "һ"}}, // һ is not h
+    {"о", {"ә", "ө"}},
+    {"ч", {"ҷ", "ҹ"}},
+    {"ь", {"ъ"}},
+    //
+    // Arabic
+    //
+    // This renders weirdly in text editors, but is valid code.
+    {"ا", {"أ", "إ", "آ", "ء"}},
+    {"ب", {"پ"}},
+    {"ج", {"چ"}},
+    {"ز", {"ژ"}},
+    {"ف", {"ڤ"}},
+    {"ك", {"گ"}},
+    {"ل", {"لا"}},
+    {"ه", {"ه"}},
+    {"و", {"ؤ"}},
+    //
+    // Hebrew
+    //
+    // Likewise, this will render oddly, but is still valid code.
+    {"ג",{"ג׳"}},
+    {"ז",{"ז׳"}},
+    {"ח",{"ח׳"}},
+    {"צ׳",{"צ׳"}},
+    {"ת",{"ת׳"}},
+    {"י",{"ײַ"}},
+    {"י", {"ײ"}},
+    {"ח", {"ױ"}},
+    {"ו", {"װ"}},
+    //
+    // Numbers
+    //
+    {"0", {"∅", "ⁿ", "⁰"}},
+    {"1", {"¹", "½", "⅓", "¼", "⅕", "⅙", "⅐", "⅛", "⅑", "⅒"}},
+    {"2", {"²", "⅖", "⅔"}},
+    {"3", {"³", "⅗", "¾", "⅜"}},
+    {"4", {"⁴", "⅘", "⁵", "⅝", "⅚"}},
+    {"5", {"⁵", "⅝", "⅚"}},
+    {"6", {"⁶"}},
+    {"7", {"⁷", "⅞"}},
+    {"8", {"⁸"}},
+    {"9", {"⁹"}},
+    //
+    // Punctuation
+    //
+    {R"(-)", {"—", "–", "·"}},
+    {R"(?)", {"¿", "‽"}},
+    {R"(')", {"‘", "’", "‚", "‹", "›"}},
+    {R"(!)", {"¡"}},
+    {R"(")", {"“", "”", "„", "«", "»"}},
+    {R"(/)", {"÷"}},
+    {R"(#)", {"№"}},
+    {R"(%)", {"‰", "℅"}},
+    {R"(^)", {"↑", "←", "→", "↓"}},
+    {R"(+)", {"±"}},
+    {R"(<)", {"«", "≤", "‹", "⟨"}},
+    {R"(=)", {"∞", "≠", "≈"}},
+    {R"(>)", {"⟩", "»", "≥", "›"}},
+};
+
+}

src/platforminputcontextplugin/main.cpp

+/*
+ *  Copyright 2020 Carson Black <uhhadd@gmail.com>
+ *
+ *  This library is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU Lesser General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License or ( at
+ *  your option ) version 3 or, at the discretion of KDE e.V. ( which shall
+ *  act as a proxy as in section 14 of the GPLv3 ), any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Library General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public License
+ *  along with this library; see the file COPYING.LIB.  If not, write to
+ *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ *  Boston, MA 02110-1301, USA.
+ */
+
+#include <QObject>
+#include <QtPlugin>
+#include <qpa/qplatforminputcontextplugin_p.h>
+
+#include "plasmaimcontext.h"
+
+QT_BEGIN_NAMESPACE
+
+class PlasmaIM : public QPlatformInputContextPlugin
+{
+    Q_OBJECT
+    Q_PLUGIN_METADATA(IID QPlatformInputContextFactoryInterface_iid FILE "plasmaim.json")
+
+public:
+    QPlatformInputContext *create(const QString&, const QStringList&) Q_DECL_OVERRIDE;
+};
+
+QPlatformInputContext *PlasmaIM::create(const QString& system, const QStringList&)
+{
+    if (system == "plasmaim") {
+        return new PlasmaIMContext;
+    }
+
+    return nullptr;
+}
+
+QT_END_NAMESPACE
+
+#include "main.moc"

src/platforminputcontextplugin/plasma-key-data.pc.in

+prefix=@CMAKE_INSTALL_PREFIX@
+includedir=${prefix}/include
+
+Name: PlasmaKeyData
+Description: Plasma's key data used for key-holding behaviour
+Version: 1.0
+Cflags: -I${includedir}/PlasmaKeyData
+Libs:
\ No newline at end of file

src/platforminputcontextplugin/plasmaim.json

+{
+    "Keys": [ "plasmaim" ]
+}

src/platforminputcontextplugin/plasmaimcontext.cpp

+/*
+ *  Copyright 2020 Carson Black <uhhadd@gmail.com>
+ *
+ *  This library is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU Lesser General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License or ( at
+ *  your option ) version 3 or, at the discretion of KDE e.V. ( which shall
+ *  act as a proxy as in section 14 of the GPLv3 ), any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Library General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public License
+ *  along with this library; see the file COPYING.LIB.  If not, write to
+ *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ *  Boston, MA 02110-1301, USA.
+ */
+
+/// Qt Utilities
+#include <QGuiApplication>
+#include <QInputMethod>
+#include <QInputMethodEvent>
+#include <QKeyEvent>
+#include <QQuickWindow>
+#include <QStringBuilder>
+#include <QToolTip>
+
+// Widgets for the popup
+#include <QGridLayout>
+#include <QLabel>
+#include <QPushButton>
+
+#include "data/plasmakeydata.h"
+
+#include "plasmaimcontext.h"
+
+static QList<TooltipData> dataForIndex(const QString &ch, bool upperCase)
+{
+    QList<TooltipData> ret;
+    int i = 0;
+    for (auto item : KeyData::KeyMappings[ch]) {
+        ret << TooltipData {upperCase ? item.toUpper() : item, QString::number((i + 1) < 10 ? (i + 1) : 0, 10), i};
+        i++;
+    }
+    return ret;
+}
+
+PlasmaIMContext::PlasmaIMContext()
+{
+    connect(watcher.data(), &KConfigWatcher::configChanged, this, &PlasmaIMContext::configChangedHandler);
+}
+
+PlasmaIMContext::~PlasmaIMContext()
+{
+    if (!popup.isNull()) {
+        popup->hide();
+        popup->deleteLater();
+    }
+}
+
+bool PlasmaIMContext::isValid() const
+{
+    return true;
+}
+
+void PlasmaIMContext::cleanUpState()
+{
+    if (!popup.isNull()) {
+        popup->hide();
+        popup->deleteLater();
+    }
+
+    isPreHold = false;
+    preHoldText = QString();
+}
+
+void PlasmaIMContext::setFocusObject(QObject *object)
+{
+    m_focusObject = object;
+}
+
+void PlasmaIMContext::configChangedHandler(const KConfigGroup&, const QByteArrayList&)
+{
+    config->reparseConfiguration();
+}
+
+void PlasmaIMContext::showPopup(const QList<TooltipData> &text)
+{
+    QPoint position;
+    QWindow *parentWin = nullptr;
+
+    auto im = QGuiApplication::inputMethod();
+    if (im != nullptr && im->cursorRectangle().isValid()) {
+        position = im->cursorRectangle().topRight().toPoint();
+        parentWin = QGuiApplication::focusWindow();
+    }
+
+    auto isRtl =
+        text[0].character[0].script() == QChar::Script_Arabic || text[0].character[0].script() == QChar::Script_Hebrew;
+
+    popup = new QWidget;
+    auto grid = new QGridLayout(popup.data());
+    popup->setLayoutDirection(isRtl ? Qt::RightToLeft : Qt::LeftToRight);
+    popup->setLayout(grid);
+    int col = 0;
+    for (auto item : text) {
+        auto label = new QLabel(item.character, popup.data());
+        auto button = new QPushButton(item.number, popup.data());
+
+        button->setMaximumWidth(button->height());
+
+        grid->addWidget(label, 0, col, Qt::AlignCenter);
+        grid->addWidget(button, 1, col, Qt::AlignHCenter);
+
+        connect(button, &QPushButton::clicked, [=]() {
+            applyReplacement(item.character);
+            popup->hide();
+            popup->deleteLater();
+        });
+
+        col++;
+    }
+
+    connect(parentWin, &QWindow::activeChanged, this, &PlasmaIMContext::cleanUpState, Qt::UniqueConnection);
+
+    if (parentWin != nullptr) {
+        popup->setWindowFlags(Qt::WindowDoesNotAcceptFocus | Qt::ToolTip);
+        popup->adjustSize();
+        popup->move(position + parentWin->framePosition() - QPoint((isRtl ? popup->width() : 0), 0));
+        popup->show();
+    }
+}
+
+void PlasmaIMContext::applyReplacement(const QString &data)
+{
+    if (m_focusObject != nullptr) {
+        QInputMethodEvent ev;
+        ev.setCommitString(data, -1, 1);
+        QCoreApplication::sendEvent(m_focusObject, &ev);
+    }
+}
+
+bool PlasmaIMContext::filterEvent(const QEvent *event)
+{
+    bool isAccent = keyboard.readEntry("KeyRepeat", "accent") == QLatin1String("accent");
+    bool isNothing = keyboard.readEntry("KeyRepeat", "accent") == QLatin1String("nothing");
+
+    if (!isAccent && !isNothing) {
+        return false;
+    }
+
+    if (event->type() == QEvent::KeyPress) {
+        auto ev = static_cast<const QKeyEvent *>(event);
+
+        // this is the state when we have a held key
+        if (isPreHold) {
+            if (ev->isAutoRepeat() && ev->text() == preHoldText)
+                return true;
+
+            if (ev->key() < 0x30 || 0x39 < ev->key()) {
+                cleanUpState();
+                return false;
+            }
+
+            auto str = preHoldText;
+            bool isUpper = str.isUpper();
+            str = str.toLower();
+
+            int key = ev->key() - 0x30;
+            if (key == 0) {
+                key = 10;
+            }
+            if (KeyData::KeyMappings[str].count() < key) {
+                cleanUpState();
+                return false;
+            }
+
+            auto data = KeyData::KeyMappings[str][key - 1];
+            applyReplacement(isUpper ? data.toUpper() : data);
+            isPreHold = false;
+            preHoldText = QString();
+            popup->hide();
+            return true;
+        }
+
+        // this is the state before we have a held key
+        if (ev->isAutoRepeat()) {
+            if (isNothing)
+                return true;
+
+            if (!isPreHold) {
+                if (ev->text().isEmpty())
+                    return false;
+                if (!KeyData::KeyMappings.contains(ev->text().toLower()))
+                    return false;
+
+                auto tooltipText = dataForIndex(ev->text().toLower(), ev->text().isUpper());
+                showPopup(tooltipText);
+
+                isPreHold = true;
+                preHoldText = ev->text();
+            }
+
+            return true;
+        }
+
+        cleanUpState();
+    }
+
+    return false;
+}

src/platforminputcontextplugin/plasmaimcontext.h

+/*
+ *  Copyright 2020 Carson Black <uhhadd@gmail.com>
+ *
+ *  This library is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU Lesser General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License or ( at
+ *  your option ) version 3 or, at the discretion of KDE e.V. ( which shall
+ *  act as a proxy as in section 14 of the GPLv3 ), any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Library General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public License
+ *  along with this library; see the file COPYING.LIB.  If not, write to
+ *  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ *  Boston, MA 02110-1301, USA.
+ */
+
+#ifndef PLASMAIMCONTEXT_H
+#define PLASMAIMCONTEXT_H
+
+#include <QPointer>
+#include <QWidget>
+
+#include <KConfigGroup>
+#include <KSharedConfig>
+#include <KConfigWatcher>
+
+#include <qpa/qplatforminputcontext.h>
+
+QT_BEGIN_NAMESPACE
+
+struct TooltipData {
+    QString character;
+    QString number;
+    int idx;
+};
+
+class PlasmaIMContext : public QPlatformInputContext
+{
+    Q_OBJECT
+
+public:
+    PlasmaIMContext();
+    ~PlasmaIMContext();
+
+    bool isValid() const Q_DECL_OVERRIDE;
+    void setFocusObject(QObject *object) Q_DECL_OVERRIDE;
+    bool filterEvent(const QEvent* event) Q_DECL_OVERRIDE;
+
+private:
+
+    void cleanUpState();
+    void applyReplacement(const QString& data);
+    void showPopup(const QList<TooltipData>& text);
+    void configChangedHandler(const KConfigGroup& grp, const QByteArrayList& names);
+
+    QPointer<QWidget> popup;
+    QPointer<QObject> m_focusObject = nullptr;
+
+    bool isPreHold = false;
+    QString preHoldText = QString();
+    KSharedConfig::Ptr config = KSharedConfig::openConfig( QStringLiteral("kcminputrc") );
+    KConfigGroup keyboard = KConfigGroup(config, "Keyboard");
+    KConfigWatcher::Ptr watcher = KConfigWatcher::create(config);
+
+};
+
+QT_END_NAMESPACE
+
+#endif