From be1c3e913648b874931d59a07dc83012abb890fa Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Wed, 8 Jul 2020 21:31:29 -0400
Subject: [PATCH] Ensures key state is cleared upon activation changes.

---
 OSBindings/Qt/mainwindow.cpp | 14 ++++++++++++++
 OSBindings/Qt/mainwindow.h   |  2 ++
 2 files changed, 16 insertions(+)

diff --git a/OSBindings/Qt/mainwindow.cpp b/OSBindings/Qt/mainwindow.cpp
index d0da4b204..ec87b29c6 100644
--- a/OSBindings/Qt/mainwindow.cpp
+++ b/OSBindings/Qt/mainwindow.cpp
@@ -757,6 +757,20 @@ void MainWindow::setWindowTitle() {
 
 // MARK: - Event Processing
 
+void MainWindow::changeEvent(QEvent *event) {
+	// Clear current key state upon any window activation change.
+	if(event->type() == QEvent::ActivationChange) {
+		const auto keyboardMachine = machine->keyboard_machine();
+		if(keyboardMachine) {
+			keyboardMachine->clear_all_keys();
+			return;
+		}
+	}
+
+	event->ignore();
+}
+
+
 void MainWindow::keyPressEvent(QKeyEvent *event) {
 	processEvent(event);
 }
diff --git a/OSBindings/Qt/mainwindow.h b/OSBindings/Qt/mainwindow.h
index e11d82844..f158e613d 100644
--- a/OSBindings/Qt/mainwindow.h
+++ b/OSBindings/Qt/mainwindow.h
@@ -74,6 +74,8 @@ class MainWindow : public QMainWindow, public Outputs::Speaker::Speaker::Delegat
 
 		bool processEvent(QKeyEvent *);
 
+		void changeEvent(QEvent *) override;
+
 	private slots:
 		void startMachine();