Forward all scroll events in editor/viewer areas to their text area widgets (#1425)

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