diff -r 5d201ee4a9c3 -r b05af0bab735 src/main.cpp
--- a/src/main.cpp	Tue Jun 07 01:37:26 2022 +0300
+++ b/src/main.cpp	Tue Jun 07 20:44:19 2022 +0300
@@ -1,6 +1,7 @@
 #include <QApplication>
 #include <QFileDialog>
 #include <QMessageBox>
+#include <QMdiSubWindow>
 #include "mainwindow.h"
 #include "ui_mainwindow.h"
 #include "version.h"
@@ -126,7 +127,13 @@
 
 static EditorTabWidget* currentTabWidget(Ui_MainWindow* ui)
 {
-	return qobject_cast<EditorTabWidget*>(ui->tabs->currentWidget());
+	QMdiSubWindow* activeSubWindow = ui->mdiArea->activeSubWindow();
+	if (activeSubWindow == nullptr) {
+		return nullptr;
+	}
+	else {
+		return qobject_cast<EditorTabWidget*>(activeSubWindow->widget());
+	}
 };
 
 
@@ -141,12 +148,14 @@
 
 static void handleTabCloseButton(Ui_MainWindow* ui, DocumentManager* documents, int tabIndex)
 {
+	/*
 	if (tabIndex >= 0 and tabIndex < ui->tabs->count()) {
 		EditorTabWidget* tab = qobject_cast<EditorTabWidget*>(ui->tabs->widget(tabIndex));
 		if (tab != nullptr) {
 			closeDocument(documents, tab);
 		}
 	}
+	*/
 }
 
 static std::optional<ModelId> findCurrentModelId(Ui_MainWindow* ui, DocumentManager* documents)
@@ -201,8 +210,8 @@
 	Ui_MainWindow* ui,
 	const gl::RenderPreferences* renderPreferences)
 {
-	for (int i = 0; i < ui->tabs->count(); i += 1) {
-		EditorTabWidget* tab = qobject_cast<EditorTabWidget*>(ui->tabs->widget(i));
+	for (QMdiSubWindow* subWindow : ui->mdiArea->subWindowList()) {
+		EditorTabWidget* tab = qobject_cast<EditorTabWidget*>(subWindow->widget());
 		if (tab != nullptr) {
 			tab->canvas->setRenderPreferences(*renderPreferences);
 		}
@@ -275,6 +284,7 @@
 		updateRecentlyOpenedDocumentsMenu();
 		colorTable = loadColors(&libraries);
 		updateRenderPreferences(&ui, &renderPreferences);
+		ui.mdiArea->setViewMode(static_cast<QMdiArea::ViewMode>(settings.viewMode()));
 		ui.retranslateUi(&mainWindow);
 	};
 	const auto addRecentlyOpenedFile = [&](const QString& path){
@@ -302,15 +312,13 @@
 				mainWindow.statusBar()->showMessage(newStatusText);
 			});
 		const QFileInfo fileInfo{*documents.modelPath(modelId)};
-		ui.tabs->addTab(document, tabName(fileInfo));
-		ui.tabs->setCurrentWidget(document);
+		QMdiSubWindow* subWindow = ui.mdiArea->addSubWindow(document);
+		subWindow->setWindowTitle(tabName(fileInfo));
+		subWindow->show();
 		document->restoreSplitterState(documentSplitterState);
 	};
-	const auto newModel = [&openModelForEditing](DocumentManager* documents){
-		openModelForEditing(documents->newModel());
-	};
-	QObject::connect(ui.actionNew, &QAction::triggered, [&newModel, &documents]{
-		newModel(&documents);
+	QObject::connect(ui.actionNew, &QAction::triggered, [&]{
+		openModelForEditing(documents.newModel());
 	});
 	QObject::connect(ui.actionOpen, &QAction::triggered, [&]{
 		const QString path = getOpenModelPath(&mainWindow);
@@ -378,7 +386,10 @@
 				QString error;
 				QTextStream errorStream{&error};
 				documents.setModelPath(*modelId, newPath, libraries, errorStream);
-				ui.tabs->setTabText(ui.tabs->currentIndex(), QFileInfo{newPath}.fileName());
+				QMdiSubWindow* const subWindow = ui.mdiArea->currentSubWindow();
+				if (subWindow != nullptr) {
+					subWindow->setWindowTitle(tabName(QFileInfo{newPath}));
+				}
 				save(*modelId);
 			}
 		}
@@ -398,9 +409,11 @@
 			}
 		}
 	});
-	QObject::connect(ui.tabs, &QTabWidget::tabCloseRequested, [&](int index){
+	/*
+	QObject::connect(ui.mdiArea, &QTabWidget::tabCloseRequested, [&](int index){
 		handleTabCloseButton(&ui, &documents, index);
 	});
+	*/
 	QObject::connect(ui.actionDrawAxes, &QAction::triggered, [&](bool drawAxes){
 		renderPreferences.drawAxes = drawAxes;
 		saveSettings();
@@ -418,7 +431,6 @@
 	mainWindow.restoreGeometry(settings.mainWindowGeometry());
 	restoreSettings();
 	updateRenderPreferences(&ui, &renderPreferences);
-	newModel(&documents);
 	mainWindow.show();
 	const int result = app.exec();
 	saveSettings();