diff -r 29dc03eceb5f -r ce0c9f2e6b9c src/mainwindow.cpp
--- a/src/mainwindow.cpp	Thu Jan 11 11:41:40 2018 +0200
+++ b/src/mainwindow.cpp	Thu Jan 11 15:09:44 2018 +0200
@@ -77,17 +77,11 @@
 	g_win = this;
 	ui.setupUi(this);
 	m_updatingTabs = false;
-	m_renderer = new GLRenderer(this);
 	m_tabs = new QTabBar;
 	m_tabs->setTabsClosable(true);
 	ui.verticalLayout->insertWidget(0, m_tabs);
 
 	createBlankDocument();
-	m_renderer->setDocument(m_currentDocument);
-
-	// Stuff the renderer into its frame
-	QVBoxLayout* rendererLayout = new QVBoxLayout(ui.rendererFrame);
-	rendererLayout->addWidget(renderer());
 
 	connect(ui.objectList, SIGNAL(itemSelectionChanged()), this, SLOT(selectionChanged()));
 	connect(ui.objectList, SIGNAL(itemDoubleClicked(QListWidgetItem*)), this, SLOT(objectListDoubleClicked(QListWidgetItem*)));
@@ -117,7 +111,6 @@
 	updateTitle();
 	loadShortcuts();
 	setMinimumSize(300, 200);
-	connect(qApp, SIGNAL(aboutToQuit()), this, SLOT(doLastSecondCleanup()));
 	connect(
 		ui.ringToolSegments, SIGNAL(valueChanged(int)),
 		this, SLOT(circleToolSegmentsChanged())
@@ -186,6 +179,10 @@
 
 MainWindow::~MainWindow()
 {
+	for (GLRenderer* renderer : m_renderers.values())
+		delete renderer;
+
+	delete &ui;
 	g_win = nullptr;
 }
 
@@ -222,14 +219,6 @@
 
 // ---------------------------------------------------------------------------------------------------------------------
 //
-void MainWindow::doLastSecondCleanup()
-{
-	delete m_renderer;
-	delete &ui;
-}
-
-// ---------------------------------------------------------------------------------------------------------------------
-//
 void MainWindow::updateRecentFilesMenu()
 {
 	// First, clear any items in the recent files menu
@@ -319,7 +308,7 @@
 
 	// Recompile all Bézier curves, the changing grid affects their precision.
 	for (LDObjectIterator<LDBezierCurve> it(m_currentDocument); it.isValid(); ++it)
-		renderer()->compileObject(it);
+		currentRenderer()->compileObject(it);
 }
 
 // ---------------------------------------------------------------------------------------------------------------------
@@ -457,7 +446,7 @@
 			case OBJ_Overlay:
 			{
 				LDOverlay* ovl = static_cast<LDOverlay*>(obj);
-				descr = format("[%1] %2(%3, %4), %5 x %6", renderer()->cameraName((ECamera) ovl->camera()),
+				descr = format("[%1] %2(%3, %4), %5 x %6", currentRenderer()->cameraName((ECamera) ovl->camera()),
 					Basename(ovl->fileName()), ovl->x(), ovl->y(),
 					ovl->width(), ovl->height());
 				break;
@@ -553,9 +542,9 @@
 	removeDuplicates(compound);
 
 	for (LDObject* obj : compound)
-		renderer()->compileObject(obj);
+		currentRenderer()->compileObject(obj);
 
-	renderer()->update();
+	currentRenderer()->update();
 }
 
 // ---------------------------------------------------------------------------------------------------------------------
@@ -591,7 +580,7 @@
 			continue; // uncolored object
 
 		obj->setColor(color);
-		renderer()->compileObject(obj);
+		currentRenderer()->compileObject(obj);
 	}
 
 	endAction();
@@ -616,8 +605,8 @@
 //
 void MainWindow::doFullRefresh()
 {
-	buildObjectList();
-	m_renderer->hardRefresh();
+	this->buildObjectList();
+	this->currentRenderer()->hardRefresh();
 }
 
 // ---------------------------------------------------------------------------------------------------------------------
@@ -627,7 +616,7 @@
 void MainWindow::refresh()
 {
 	buildObjectList();
-	m_renderer->update();
+	currentRenderer()->update();
 }
 
 // ---------------------------------------------------------------------------------------------------------------------
@@ -782,7 +771,7 @@
 		contextMenu->addAction(ui.actionSubfileSelection);
 	}
 
-	if (renderer()->camera() != EFreeCamera)
+	if (currentRenderer()->camera() != EFreeCamera)
 	{
 		contextMenu->addSeparator();
 		contextMenu->addAction(ui.actionSetDrawDepth);
@@ -813,7 +802,7 @@
 //
 void MainWindow::updateEditModeActions()
 {
-	const EditModeType mode = renderer()->currentEditModeType();
+	const EditModeType mode = currentRenderer()->currentEditModeType();
 	ui.actionModeSelect->setChecked(mode == EditModeType::Select);
 	ui.actionModeDraw->setChecked(mode == EditModeType::Draw);
 	ui.actionModeRectangle->setChecked(mode == EditModeType::Rectangle);
@@ -894,7 +883,7 @@
 // Adds a message to the renderer's message manager.
 void MainWindow::addMessage(QString msg)
 {
-	m_renderer->messageLog()->addLine(msg);
+	this->currentRenderer()->messageLog()->addLine(msg);
 }
 
 // ============================================================================
@@ -1058,9 +1047,9 @@
 
 // ---------------------------------------------------------------------------------------------------------------------
 //
-GLRenderer* MainWindow::renderer()
+GLRenderer* MainWindow::currentRenderer()
 {
-	return m_renderer;
+	return m_renderers[m_currentDocument];
 }
 
 // ---------------------------------------------------------------------------------------------------------------------
@@ -1231,9 +1220,17 @@
 	connect(document->history(), SIGNAL(undone()), this, SLOT(historyTraversed()));
 	connect(document->history(), SIGNAL(redone()), this, SLOT(historyTraversed()));
 	connect(document->history(), SIGNAL(stepAdded()), this, SLOT(updateActions()));
+	connect(document, SIGNAL(closed()), this, SLOT(documentClosed()));
+
+	GLRenderer* renderer = new GLRenderer {document, this};
+	m_renderers[document] = renderer;
+	ui.rendererStack->addWidget(renderer);
 
 	if (not cache)
+	{
+		changeDocument(document);
 		document->openForEditing();
+	}
 
 	return document;
 }
@@ -1251,7 +1248,8 @@
 //
 void MainWindow::changeDocument(LDDocument* document)
 {
-	// Implicit files were loaded for caching purposes and may never be switched to.
+	// Implicit files were loaded for caching purposes and may
+	// not be switched to.
 	if (document and document->isCache())
 		return;
 
@@ -1263,8 +1261,7 @@
 		updateDocumentListItem(document);
 		buildObjectList();
 		updateTitle();
-		m_renderer->setDocument(document);
-		m_renderer->compiler()->needMerge();
+		ui.rendererStack->setCurrentWidget(m_renderers[document]);
 		print("Changed document to %1", document->getDisplayName());
 	}
 }
@@ -1295,24 +1292,38 @@
 
 // ---------------------------------------------------------------------------------------------------------------------
 //
-void MainWindow::currentDocumentClosed()
+void MainWindow::documentClosed()
 {
-	LDDocument* old = currentDocument();
+	LDDocument* document = qobject_cast<LDDocument*>(sender());
+
+	if (not document)
+		return;
+
+	if (document == currentDocument())
+	{
+		LDDocument* previousCurrentDocument = currentDocument();
 
-	// Find a replacement document to use
-	for (LDDocument* doc : m_documents->allDocuments())
-	{
-		if (doc != old and not doc->isCache())
+		// Find a replacement document to use
+		for (LDDocument* document : m_documents->allDocuments())
 		{
-			changeDocument(doc);
-			break;
+			if (document != previousCurrentDocument and not document->isCache())
+			{
+				changeDocument(document);
+				break;
+			}
+		}
+
+		if (currentDocument() == previousCurrentDocument)
+		{
+			// Failed to change to a suitable document, open a new one.
+			createBlankDocument();
 		}
 	}
 
-	if (currentDocument() == old)
+	if (m_renderers.contains(document))
 	{
-		// Failed to change to a suitable document, open a new one.
-		createBlankDocument();
+		delete m_renderers[document];
+		m_renderers.remove(document);
 	}
 }