Add scroll event filters to forward from margin area to plaintextedit.

src/SeerPlainTextEdit.cpp

@@ -0,0 +1,41 @@
+#include "SeerPlainTextEdit.h"
+
+SeerPlainTextEdit::SeerPlainTextEdit(const QString& text, QWidget* parent) : QPlainTextEdit(text, parent) {
+}
+
+SeerPlainTextEdit::SeerPlainTextEdit(QWidget* parent) : QPlainTextEdit(parent) {
+}
+
+SeerPlainTextEdit::~SeerPlainTextEdit () {
+}
+
+void SeerPlainTextEdit::forwardViewportEvent(QEvent* event) {
+
+    viewportEvent(event);
+}
+
+
+
+SeerPlainTextWheelEventForwarder::SeerPlainTextWheelEventForwarder (SeerPlainTextEdit* target ) : QObject(), _target(target) {
+}
+
+SeerPlainTextWheelEventForwarder::~SeerPlainTextWheelEventForwarder() {
+    _target = NULL;
+}
+
+bool SeerPlainTextWheelEventForwarder::eventFilter (QObject* obj, QEvent* event) {
+
+    Q_UNUSED(obj);
+
+    if (_target == 0) {
+        return false;
+    }
+
+    if (event->type() == QEvent::Wheel) {
+        _target->forwardViewportEvent(event);
+    }
+
+    // do not filter the event
+    return false;
+}
+