diff --git a/toonz/sources/toonz/main.cpp b/toonz/sources/toonz/main.cpp
index 7e6d03c..6b87580 100644
--- a/toonz/sources/toonz/main.cpp
+++ b/toonz/sources/toonz/main.cpp
@@ -629,7 +629,6 @@ int main(int argc, char *argv[]) {
   QString currentStyle = Preferences::instance()->getCurrentStyleSheetPath();
   a.setStyleSheet(currentStyle);
 
-  TApp::instance()->setMainWindow(&w);
   w.setWindowTitle(applicationFullName);
   if (TEnv::getIsPortable()) {
     splash.showMessage(offsetStr + "Starting OpenToonz Portable ...",
diff --git a/toonz/sources/toonz/mainwindow.cpp b/toonz/sources/toonz/mainwindow.cpp
index 9388982..26e4b63 100644
--- a/toonz/sources/toonz/mainwindow.cpp
+++ b/toonz/sources/toonz/mainwindow.cpp
@@ -377,6 +377,9 @@ MainWindow::MainWindow(const QString &argumentLayoutFileName, QWidget *parent,
     , m_saveSettingsOnQuit(true)
     , m_oldRoomIndex(0)
     , m_layoutName("") {
+  // store a main window pointer in advance of making its contents
+  TApp::instance()->setMainWindow(this);
+
   m_toolsActionGroup = new QActionGroup(this);
   m_toolsActionGroup->setExclusive(true);
   m_currentRoomsChoice = Preferences::instance()->getCurrentRoomChoice();
@@ -2416,9 +2419,9 @@ RecentFiles::~RecentFiles() {}
 
 void RecentFiles::addFilePath(QString path, FileType fileType) {
   QList<QString> files =
-      (fileType == Scene) ? m_recentScenes : (fileType == Level)
-                                                 ? m_recentLevels
-                                                 : m_recentFlipbookImages;
+      (fileType == Scene)
+          ? m_recentScenes
+          : (fileType == Level) ? m_recentLevels : m_recentFlipbookImages;
   int i;
   for (i = 0; i < files.size(); i++)
     if (files.at(i) == path) files.removeAt(i);
@@ -2543,9 +2546,9 @@ void RecentFiles::saveRecentFiles() {
 
 QList<QString> RecentFiles::getFilesNameList(FileType fileType) {
   QList<QString> files =
-      (fileType == Scene) ? m_recentScenes : (fileType == Level)
-                                                 ? m_recentLevels
-                                                 : m_recentFlipbookImages;
+      (fileType == Scene)
+          ? m_recentScenes
+          : (fileType == Level) ? m_recentLevels : m_recentFlipbookImages;
   QList<QString> names;
   int i;
   for (i = 0; i < files.size(); i++) {
@@ -2572,9 +2575,9 @@ void RecentFiles::refreshRecentFilesMenu(FileType fileType) {
     menu->setEnabled(false);
   else {
     CommandId clearActionId =
-        (fileType == Scene) ? MI_ClearRecentScene : (fileType == Level)
-                                                        ? MI_ClearRecentLevel
-                                                        : MI_ClearRecentImage;
+        (fileType == Scene)
+            ? MI_ClearRecentScene
+            : (fileType == Level) ? MI_ClearRecentLevel : MI_ClearRecentImage;
     menu->setActions(names);
     menu->addSeparator();
     QAction *clearAction = CommandManager::instance()->getAction(clearActionId);
diff --git a/toonz/sources/toonz/sceneviewer.cpp b/toonz/sources/toonz/sceneviewer.cpp
index 0495f07..1f50118 100644
--- a/toonz/sources/toonz/sceneviewer.cpp
+++ b/toonz/sources/toonz/sceneviewer.cpp
@@ -83,6 +83,7 @@
 #endif
 #include <QGLContext>
 #include <QOpenGLFramebufferObject>
+#include <QMainWindow>
 
 #include "sceneviewer.h"
 
@@ -92,6 +93,19 @@ void drawSpline(const TAffine &viewMatrix, const TRect &clipRect, bool camera3d,
 //-------------------------------------------------------------------------------
 namespace {
 
+int l_mainDisplayListsSpaceId =
+    -1;  //!< Display lists space id associated with SceneViewers
+std::set<TGlContext>
+    l_contexts;  //!< Stores every SceneViewer context (see ~SceneViewer)
+
+//-------------------------------------------------------------------------------
+
+struct DummyProxy : public TGLDisplayListsProxy {
+  ~DummyProxy() {}
+  void makeCurrent() {}
+  void doneCurrent() {}
+};
+
 //-------------------------------------------------------------------------------
 
 double getActualFrameRate() {
@@ -532,6 +546,12 @@ void SceneViewer::setVisual(const ImagePainter::VisualSettings &settings) {
 
 SceneViewer::~SceneViewer() {
   if (m_fbo) delete m_fbo;
+
+  // release all the registered context (once when exit the software)
+  std::set<TGlContext>::iterator ct, cEnd(l_contexts.end());
+  for (ct = l_contexts.begin(); ct != cEnd; ++ct)
+    TGLDisplayListsManager::instance()->releaseContext(*ct);
+  l_contexts.clear();
 }
 
 //-------------------------------------------------------------------------------
@@ -825,6 +845,8 @@ double SceneViewer::getHGuide(int index) { return m_hRuler->getGuide(index); }
 void SceneViewer::initializeGL() {
   initializeOpenGLFunctions();
 
+  registerContext();
+
   // to be computed once through the software
   if (m_lutCalibrator) {
     m_lutCalibrator->initialize();
@@ -2580,3 +2602,45 @@ void SceneViewer::onContextAboutToBeDestroyed() {
   m_lutCalibrator->cleanup();
   doneCurrent();
 }
+
+//-----------------------------------------------------------------------------
+// called from SceneViewer::initializeGL()
+
+void SceneViewer::registerContext() {
+  // release the old context, if any
+  // this will be happen when dock / float the viewer panel.
+  bool hasOldContext;
+#ifdef _WIN32
+  hasOldContext =
+      (m_currentContext.first != nullptr && m_currentContext.second != nullptr);
+#else
+  hasOldContext = m_currentContext != nullptr;
+#endif
+  if (hasOldContext) {
+    int ret = l_contexts.erase(m_currentContext);
+    if (ret)
+      TGLDisplayListsManager::instance()->releaseContext(m_currentContext);
+  }
+
+  // then, register context and the space Id correspondent to it.
+  int displayListId;
+  if (TApp::instance()->getMainWindow() &&
+      TApp::instance()->getMainWindow()->isAncestorOf(this) &&
+      QThread::currentThread() == qGuiApp->thread()) {
+    // obtain displaySpaceId for main thread
+    if (l_mainDisplayListsSpaceId == -1)
+      l_mainDisplayListsSpaceId =
+          TGLDisplayListsManager::instance()->storeProxy(new DummyProxy);
+
+    displayListId = l_mainDisplayListsSpaceId;
+  }
+  // for the other cases (such as for floating viewer), it can't share the
+  // context so
+  // obtain different id
+  else
+    displayListId =
+        TGLDisplayListsManager::instance()->storeProxy(new DummyProxy);
+  TGlContext tglContext(tglGetCurrentContext());
+  TGLDisplayListsManager::instance()->attachContext(displayListId, tglContext);
+  l_contexts.insert(tglContext);
+}
diff --git a/toonz/sources/toonz/sceneviewer.h b/toonz/sources/toonz/sceneviewer.h
index 97a3066..cfd4906 100644
--- a/toonz/sources/toonz/sceneviewer.h
+++ b/toonz/sources/toonz/sceneviewer.h
@@ -168,9 +168,12 @@ class SceneViewer final : public GLWidgetForHighDpi,
 
   QMatrix4x4 m_projectionMatrix;
 
+  // Used for texture management.
+  // Changing dock / float state of the panel will alter the context.
+  // So discarding the resources in old context in initializeGL.
+  TGlContext m_currentContext;
+
 public:
-  // iwsw commented out temporarily
-  // Ghibli3DLutUtil* get3DLutUtil(){ return m_ghibli3DLutUtil; }
   enum ReferenceMode {
     NORMAL_REFERENCE   = 1,
     CAMERA3D_REFERENCE = 2,
@@ -381,6 +384,8 @@ protected:
 
   void setFocus() override { QWidget::setFocus(); };
 
+  void registerContext();
+
 public slots:
 
   void resetSceneViewer();