Add Shift+Scroll horizontal scrolling (#1090)

* Add Shift+Scroll horizontal scrolling

* Refactor code

---------

Co-authored-by: dail8859 <dail8859@yahoo.com>

Author: saberoueslati

src/CMakeLists.txt

@@ -183,6 +183,8 @@ qt_add_executable(NotepadNext
 	ScintillaSorter.h ScintillaSorter.cpp
 	widgets/TabsQuickActionsBar.cpp
 	widgets/TabsQuickActionsBar.h
+	ShiftMiddleClickBlocker.h ShiftMiddleClickBlocker.cpp
+	ShiftWheelToHorizontalScrollFilter.h ShiftWheelToHorizontalScrollFilter.cpp
 )
 
 set_target_properties(NotepadNext PROPERTIES

src/ShiftMiddleClickBlocker.cpp

@@ -0,0 +1,42 @@
+/*
+ * This file is part of Notepad Next.
+ * Copyright 2026 Justin Dailey
+ *
+ * Notepad Next is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Notepad Next 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Notepad Next.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "ShiftMiddleClickBlocker.h"
+
+#include <QEvent>
+#include <QMouseEvent>
+
+ShiftMiddleClickBlocker::ShiftMiddleClickBlocker(QObject *parent)
+    : QObject(parent)
+{
+}
+
+bool ShiftMiddleClickBlocker::eventFilter(QObject *obj, QEvent *event)
+{
+    if (event->type() != QEvent::MouseButtonPress && event->type() != QEvent::MouseButtonDblClick) {
+        return QObject::eventFilter(obj, event);
+    }
+
+    auto *mouseEvent = static_cast<QMouseEvent *>(event);
+
+    if (mouseEvent->button() == Qt::MiddleButton && (mouseEvent->modifiers() & Qt::ShiftModifier)) {
+        return true;
+    }
+
+    return QObject::eventFilter(obj, event);
+}

src/ShiftMiddleClickBlocker.h

@@ -0,0 +1,32 @@
+/*
+ * This file is part of Notepad Next.
+ * Copyright 2026 Justin Dailey
+ *
+ * Notepad Next is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Notepad Next 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Notepad Next.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <QObject>
+
+class ShiftMiddleClickBlocker : public QObject
+{
+    Q_OBJECT
+
+public:
+    explicit ShiftMiddleClickBlocker(QObject *parent = nullptr);
+
+protected:
+    bool eventFilter(QObject *obj, QEvent *event) override;
+};

src/ShiftWheelToHorizontalScrollFilter.cpp

@@ -0,0 +1,72 @@
+/*
+ * This file is part of Notepad Next.
+ * Copyright 2026 Justin Dailey
+ *
+ * Notepad Next is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Notepad Next 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Notepad Next.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "ShiftWheelToHorizontalScrollFilter.h"
+
+#include <QApplication>
+#include <QEvent>
+#include <QWheelEvent>
+
+
+bool isHorizontalWheelEvent(QWheelEvent *event)
+{
+#if QT_VERSION >= QT_VERSION_CHECK(5, 15, 0)
+    return event->angleDelta().y() == 0;
+#else
+    return event->orientation() == Qt::Horizontal;
+#endif
+}
+
+ShiftWheelToHorizontalScrollFilter::ShiftWheelToHorizontalScrollFilter(QObject *parent)
+    : QObject(parent)
+{
+}
+
+bool ShiftWheelToHorizontalScrollFilter::eventFilter(QObject *obj, QEvent *event)
+{
+    if (event->type() != QEvent::Wheel) {
+        return QObject::eventFilter(obj, event);
+    }
+
+    auto *wheelEvent = static_cast<QWheelEvent *>(event);
+
+    if (!(wheelEvent->modifiers() & Qt::ShiftModifier)
+        || (wheelEvent->modifiers() & Qt::ControlModifier)
+        || isHorizontalWheelEvent(wheelEvent)) {
+        return QObject::eventFilter(obj, event);
+    }
+
+    const QPoint angleDelta(wheelEvent->angleDelta().y(), wheelEvent->angleDelta().x());
+
+    const QPoint pixelDelta(wheelEvent->pixelDelta().y(), wheelEvent->pixelDelta().x());
+
+    QWheelEvent horizontalEvent(
+        wheelEvent->position(),
+        wheelEvent->globalPosition(),
+        pixelDelta,
+        angleDelta,
+        wheelEvent->buttons(),
+        wheelEvent->modifiers() & ~Qt::ShiftModifier,
+        wheelEvent->phase(),
+        wheelEvent->inverted(),
+        wheelEvent->source(),
+        wheelEvent->pointingDevice());
+
+    QApplication::sendEvent(obj, &horizontalEvent);
+    return true;
+}

src/ShiftWheelToHorizontalScrollFilter.h

@@ -0,0 +1,32 @@
+/*
+ * This file is part of Notepad Next.
+ * Copyright 2026 Justin Dailey
+ *
+ * Notepad Next is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Notepad Next 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Notepad Next.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <QObject>
+
+class ShiftWheelToHorizontalScrollFilter : public QObject
+{
+    Q_OBJECT
+
+public:
+    explicit ShiftWheelToHorizontalScrollFilter(QObject *parent = nullptr);
+
+protected:
+    bool eventFilter(QObject *obj, QEvent *event) override;
+};

src/ZoomEventWatcher.cpp

@@ -64,4 +64,4 @@ bool ZoomEventWatcher::eventFilter(QObject *obj, QEvent *event)
     }
 
     return QObject::eventFilter(obj, event);
-}
+}

src/dialogs/MainWindow.cpp

@@ -81,6 +81,9 @@
 #include "MacroEditorDialog.h"
 
 #include "ZoomEventWatcher.h"
+#include "ShiftMiddleClickBlocker.h"
+#include "ShiftWheelToHorizontalScrollFilter.h"
+
 #include "FileDialogHelpers.h"
 
 #include "HtmlConverter.h"
@@ -94,7 +97,9 @@
 MainWindow::MainWindow(NotepadNextApplication *app) :
     ui(new Ui::MainWindow),
     app(app),
-    zoomEventWatcher(new ZoomEventWatcher(this))
+    zoomEventWatcher(new ZoomEventWatcher(this)),
+    shiftMiddleClickBlocker(new ShiftMiddleClickBlocker(this)),
+    shiftWheelToHorizontalScrollFilter(new ShiftWheelToHorizontalScrollFilter(this))
 {
     qInfo(Q_FUNC_INFO);
 
@@ -2095,6 +2100,13 @@ void MainWindow::addEditor(ScintillaNext *editor)
     connect(editor, &ScintillaNext::renamed, this, [=, this]() { updateFileStatusBasedUi(editor); });
     connect(editor, &ScintillaNext::updateUi, this, &MainWindow::updateDocumentBasedUi);
 
+    // Scintilla pastes the primary selection on middle-click. Suppress an
+    // accidental wheel-button press while Shift is held for horizontal scrolling.
+    editor->viewport()->installEventFilter(shiftMiddleClickBlocker);
+
+    // Translate shift+vertical wheel to vertical
+    editor->viewport()->installEventFilter(shiftWheelToHorizontalScrollFilter);
+
     // Watch for any zoom events (Ctrl+Scroll or pinch-to-zoom (Qt translates it as Ctrl+Scroll)) so that the event
     // can be handled before the ScintillaEditBase widget, so that it can be applied to all editors to keep zoom level equal.
     // NOTE: Need to install this on the scroll area's viewport, not on the editor widget itself...that was painful to learn

src/dialogs/MainWindow.h

@@ -40,6 +40,8 @@ class Macro;
 class Settings;
 class QuickFindWidget;
 class ZoomEventWatcher;
+class ShiftMiddleClickBlocker;
+class ShiftWheelToHorizontalScrollFilter;
 class Converter;
 class DefaultDirectoryManager;
 class TabsQuickActionsBar;
@@ -196,6 +198,8 @@ private slots:
     DefaultDirectoryManager *defaultDirectoryManager;
 
     ZoomEventWatcher *zoomEventWatcher;
+    ShiftMiddleClickBlocker *shiftMiddleClickBlocker;
+    ShiftWheelToHorizontalScrollFilter *shiftWheelToHorizontalScrollFilter;
     int zoomLevel = 0;
     int contextMenuPos = 0;
     QMenu *buildMenu(QStringList actionNames);