From 94329b334acd14cf0839113c88676157bcec7982 Mon Sep 17 00:00:00 2001
From: Veronica Berglyd Olsen <1619840+vkbo@users.noreply.github.com>
Date: Thu, 31 Aug 2023 11:40:52 +0200
Subject: [PATCH] Forward all scroll events in editor/viewer areas to their
 text area widgets (#1425)

---
 novelwriter/extensions/wheeleventfilter.py | 65 ++++++++++++++++++++++
 novelwriter/gui/doceditor.py               |  5 ++
 novelwriter/gui/docviewer.py               |  5 ++
 3 files changed, 75 insertions(+)
 create mode 100644 novelwriter/extensions/wheeleventfilter.py

diff --git a/novelwriter/extensions/wheeleventfilter.py b/novelwriter/extensions/wheeleventfilter.py
new file mode 100644
index 00000000..75340cfa
--- /dev/null
+++ b/novelwriter/extensions/wheeleventfilter.py
@@ -0,0 +1,65 @@
+"""
+novelWriter – Custom Object: Wheel Event Filter
+===============================================
+
+File History:
+Created: 2023-08-31 [2.1b2]
+
+This file is a part of novelWriter
+Copyright 2018–2023, Veronica Berglyd Olsen
+
+This program 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.
+
+This program 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 this program. If not, see <https://www.gnu.org/licenses/>.
+"""
+from __future__ import annotations
+
+from PyQt5.QtGui import QWheelEvent
+from PyQt5.QtCore import QEvent, QObject
+from PyQt5.QtWidgets import QWidget
+
+
+class WheelEventFilter(QObject):
+    """Extensions: Wheel Event Filter
+
+    An event filter that filters mouse wheel events for a widget and
+    forward them to the root widget. This solves the lack of mouse wheel
+    scrolling response in margins of widgets like the editor and viewer.
+
+    Solves: https://github.com/vkbo/novelWriter/issues/1425
+    Reference: https://stackoverflow.com/a/17739995/5825851
+    """
+
+    __slots__ = ("_parent", "_locked")
+
+    def __init__(self, parent: QWidget) -> None:
+        super().__init__(parent=parent)
+        self._parent = parent
+        self._locked = False
+        return
+
+    def eventFilter(self, object: QObject, event: QEvent) -> bool:
+        """Filter events of type QWheelEvent and forward them to the
+        parent widget's wheelEvent handler.
+        """
+        if self._locked:
+            return False
+        if isinstance(event, QWheelEvent):
+            # Recursion protection may be redundant, but a comment on
+            # StackOverflow points to Qt 5.12 as the change, and we
+            # still support Qt 5.10
+            self._locked = True
+            self._parent.wheelEvent(event)
+            self._locked = False
+        return False
+
+# END Class WheelEventFilter
diff --git a/novelwriter/gui/doceditor.py b/novelwriter/gui/doceditor.py
index 5d971ca6..c10765aa 100644
--- a/novelwriter/gui/doceditor.py
+++ b/novelwriter/gui/doceditor.py
@@ -55,6 +55,7 @@ from novelwriter.common import minmax, transferCase
 from novelwriter.constants import nwConst, nwKeyWords, nwUnicode
 from novelwriter.core.index import countWords
 from novelwriter.gui.dochighlight import GuiDocHighlighter
+from novelwriter.extensions.wheeleventfilter import WheelEventFilter
 
 if TYPE_CHECKING:  # pragma: no cover
     from novelwriter.guimain import GuiMain
@@ -178,6 +179,10 @@ class GuiDocEditor(QTextEdit):
         self.wCounterSel.setAutoDelete(False)
         self.wCounterSel.signals.countsReady.connect(self._updateSelCounts)
 
+        # Install Event Filter for Mouse Wheel
+        self.wheelEventForwarder = WheelEventFilter(self)
+        self.installEventFilter(self.wheelEventForwarder)
+
         # Finalise
         self.updateSyntaxColours()
         self.initEditor()
diff --git a/novelwriter/gui/docviewer.py b/novelwriter/gui/docviewer.py
index bbfb4c64..91992c00 100644
--- a/novelwriter/gui/docviewer.py
+++ b/novelwriter/gui/docviewer.py
@@ -47,6 +47,7 @@ from novelwriter.enum import nwItemType, nwDocAction, nwDocMode
 from novelwriter.error import logException
 from novelwriter.constants import nwUnicode
 from novelwriter.core.tohtml import ToHtml
+from novelwriter.extensions.wheeleventfilter import WheelEventFilter
 
 if TYPE_CHECKING:  # pragma: no cover
     from novelwriter.guimain import GuiMain
@@ -85,6 +86,10 @@ class GuiDocViewer(QTextBrowser):
         # Signals
         self.anchorClicked.connect(self._linkClicked)
 
+        # Install Event Filter for Mouse Wheel
+        self.wheelEventForwarder = WheelEventFilter(self)
+        self.installEventFilter(self.wheelEventForwarder)
+
         # Context Menu
         self.setContextMenuPolicy(Qt.CustomContextMenu)
         self.customContextMenuRequested.connect(self._openContextMenu)