diff --git a/toonz/sources/include/toonzqt/pickrgbutils.h b/toonz/sources/include/toonzqt/pickrgbutils.h
index abfea52..e298300 100644
--- a/toonz/sources/include/toonzqt/pickrgbutils.h
+++ b/toonz/sources/include/toonzqt/pickrgbutils.h
@@ -23,7 +23,7 @@
 //  Forward declarations
 
 class QWidget;
-class QGLWidget;
+class QOpenGLWidget;
 
 //-------------------------------------------------------------------------------
 
@@ -33,7 +33,7 @@ class QGLWidget;
     widget bounds.
 
 \warning Use this function only on plain widgets - in case your widget inherits
-         QGLWidget, invoke the overloaded function accepting a QGLWidget* type
+         QOpenGLWidget, invoke the overloaded function accepting a QOpenGLWidget* type
          instead.
 */
 QRgb DVAPI pickRGB(QWidget *widget, const QRect &rect);
@@ -42,14 +42,14 @@ inline QRgb pickRGB(QWidget *widget, const QPoint &pos)
 	return pickRGB(widget, QRect(pos.x(), pos.y(), 1, 1));
 }
 
-//! Returns the average color displayed in a QGLWidget instance across the specified rect.
+//! Returns the average color displayed in a QOpenGLWidget instance across the specified rect.
 /*! This function reads the widget's front frame buffer on given rect, and returns
     a mean of its pixels.
     
 \warning Pixel colors are undefined outside the widget's geometry.
 */
-QRgb DVAPI pickRGB(QGLWidget *widget, const QRect &rect);
-inline QRgb pickRGB(QGLWidget *widget, const QPoint &pos)
+QRgb DVAPI pickRGB(QOpenGLWidget *widget, const QRect &rect);
+inline QRgb pickRGB(QOpenGLWidget *widget, const QPoint &pos)
 {
 	return pickRGB(widget, QRect(pos.x(), pos.y(), 1, 1));
 }
diff --git a/toonz/sources/include/toonzqt/planeviewer.h b/toonz/sources/include/toonzqt/planeviewer.h
index e6cf865..e19e888 100644
--- a/toonz/sources/include/toonzqt/planeviewer.h
+++ b/toonz/sources/include/toonzqt/planeviewer.h
@@ -9,7 +9,7 @@
 #include "timage.h"
 
 // Qt includes
-#include <QGLWidget>
+#include <QOpenGLWidget>
 
 #undef DVAPI
 #undef DVVAR
@@ -44,10 +44,10 @@ class TVectorImageP;
             efficient image-drawing functions for all Toonz image types.
 */
 
-class DVAPI PlaneViewer : public QGLWidget
+class DVAPI PlaneViewer : public QOpenGLWidget
 {
 public:
-	PlaneViewer(QWidget *parent = 0);
+	PlaneViewer(QWidget *parent);
 
 	// Background functions
 	void setBgColor(const TPixel32 &color1, const TPixel32 &color2);
@@ -113,18 +113,20 @@ protected:
 	double m_zoomRange[2]; //!< Viewport zoom range (default: [-1024, 1024]).
 
 protected:
-	virtual void mouseMoveEvent(QMouseEvent *event);
-	virtual void mousePressEvent(QMouseEvent *event);
-	virtual void wheelEvent(QWheelEvent *event);
-	virtual void keyPressEvent(QKeyEvent *event);
-	virtual void resizeEvent(QResizeEvent *event);
-	virtual void hideEvent(QHideEvent *event);
+	virtual void mouseMoveEvent(QMouseEvent *event) override;
+	virtual void mousePressEvent(QMouseEvent *event) override;
+	virtual void wheelEvent(QWheelEvent *event) override;
+	virtual void keyPressEvent(QKeyEvent *event) override;
+	virtual void hideEvent(QHideEvent *event) override;
 
-	void initMatrix();
+	void initializeGL() override final;
+	void resizeGL(int width, int height) override final;
 
 private:
 	GLdouble m_matrix[16];
 	bool m_firstResize;
+	int m_width;
+	int m_height;
 };
 
 #endif //PLANE_VIEWER_H
diff --git a/toonz/sources/include/toonzqt/styleeditor.h b/toonz/sources/include/toonzqt/styleeditor.h
index ed6b804..1957d49 100644
--- a/toonz/sources/include/toonzqt/styleeditor.h
+++ b/toonz/sources/include/toonzqt/styleeditor.h
@@ -32,7 +32,7 @@
 #include <QSlider>
 #include <QToolButton>
 #include <QScrollArea>
-#include <QGLWidget>
+#include <QOpenGLWidget>
 #include <QMouseEvent>
 #include <QPointF>
 
@@ -141,7 +141,7 @@ enum CurrentWheel {
 	rightTriangle
 };
 
-class DVAPI HexagonalColorWheel : public QGLWidget
+class DVAPI HexagonalColorWheel : public QOpenGLWidget
 {
 	Q_OBJECT
 
diff --git a/toonz/sources/tnztools/hooktool.cpp b/toonz/sources/tnztools/hooktool.cpp
index 1bace70..fa457f9 100644
--- a/toonz/sources/tnztools/hooktool.cpp
+++ b/toonz/sources/tnztools/hooktool.cpp
@@ -38,7 +38,6 @@
 #include <QCoreApplication>
 
 #include <QPainter>
-#include <QGLWidget>
 
 using namespace ToolUtils;
 
diff --git a/toonz/sources/tnztools/skeletontool.cpp b/toonz/sources/tnztools/skeletontool.cpp
index ce0c906..abf7864 100644
--- a/toonz/sources/tnztools/skeletontool.cpp
+++ b/toonz/sources/tnztools/skeletontool.cpp
@@ -40,7 +40,7 @@
 // Qt includes
 #include <QCoreApplication> // Qt translation support
 #include <QPainter>
-#include <QGLWidget>
+#include <QGLWidget> // for QGLWidget::convertToGLFormat
 #include <QPainterPath>
 #include <QString>
 #include <QImage>
diff --git a/toonz/sources/tnztools/toolutils.cpp b/toonz/sources/tnztools/toolutils.cpp
index d51951c..4012322 100644
--- a/toonz/sources/tnztools/toolutils.cpp
+++ b/toonz/sources/tnztools/toolutils.cpp
@@ -41,7 +41,7 @@
 #include "tools/strokeselection.h"
 
 #include <QPainter>
-#include <QGLWidget>
+#include <QGLWidget> // for QGLWidget::convertToGLFormat
 #include <QFont>
 #include <QFontMetrics>
 
diff --git a/toonz/sources/toonz/adjustlevelspopup.cpp b/toonz/sources/toonz/adjustlevelspopup.cpp
index e1e3d4b..24f7e1d 100644
--- a/toonz/sources/toonz/adjustlevelspopup.cpp
+++ b/toonz/sources/toonz/adjustlevelspopup.cpp
@@ -111,7 +111,7 @@ public:
 	TRasterP raster() const { return m_ras; }
 	TRasterP &raster() { return m_ras; }
 
-	void paintGL()
+	void paintGL() override
 	{
 		drawBackground();
 
diff --git a/toonz/sources/toonz/adjustthicknesspopup.cpp b/toonz/sources/toonz/adjustthicknesspopup.cpp
index e7a4f2f..f6fdb69 100644
--- a/toonz/sources/toonz/adjustthicknesspopup.cpp
+++ b/toonz/sources/toonz/adjustthicknesspopup.cpp
@@ -245,7 +245,7 @@ public:
 	TVectorImageP image() const { return m_vi; }
 	TVectorImageP &image() { return m_vi; }
 
-	void paintGL()
+	void paintGL() override
 	{
 		drawBackground();
 
diff --git a/toonz/sources/toonz/antialiaspopup.cpp b/toonz/sources/toonz/antialiaspopup.cpp
index f78b406..227fb5f 100644
--- a/toonz/sources/toonz/antialiaspopup.cpp
+++ b/toonz/sources/toonz/antialiaspopup.cpp
@@ -88,7 +88,7 @@ public:
 
 	void setImage(const TImageP &img) { m_img = img; }
 
-	void paintGL()
+	void paintGL() override
 	{
 		drawBackground();
 
diff --git a/toonz/sources/toonz/binarizepopup.cpp b/toonz/sources/toonz/binarizepopup.cpp
index 0736a90..11902a8 100644
--- a/toonz/sources/toonz/binarizepopup.cpp
+++ b/toonz/sources/toonz/binarizepopup.cpp
@@ -141,7 +141,7 @@ public:
 	TRasterP raster() const { return m_ras; }
 	TRasterP &raster() { return m_ras; }
 
-	void paintGL()
+	void paintGL() override
 	{
 		pushGLWorldCoordinates();
 		drawBackground();
diff --git a/toonz/sources/toonz/brightnessandcontrastpopup.cpp b/toonz/sources/toonz/brightnessandcontrastpopup.cpp
index 2e61c9d..4a0058e 100644
--- a/toonz/sources/toonz/brightnessandcontrastpopup.cpp
+++ b/toonz/sources/toonz/brightnessandcontrastpopup.cpp
@@ -218,7 +218,7 @@ public:
 	TRasterP raster() const { return m_ras; }
 	TRasterP &raster() { return m_ras; }
 
-	void paintGL()
+	void paintGL() override
 	{
 		drawBackground();
 
diff --git a/toonz/sources/toonz/comboviewerpane.cpp b/toonz/sources/toonz/comboviewerpane.cpp
index 4553e99..5ce1d92 100644
--- a/toonz/sources/toonz/comboviewerpane.cpp
+++ b/toonz/sources/toonz/comboviewerpane.cpp
@@ -57,7 +57,6 @@
 #include <QAction>
 #include <QDialogButtonBox>
 #include <QAbstractButton>
-#include <QGLWidget>
 #include <QMouseEvent>
 #include <QWheelEvent>
 #include <QLabel>
diff --git a/toonz/sources/toonz/exportlevelpopup.cpp b/toonz/sources/toonz/exportlevelpopup.cpp
index f4b5431..01607a1 100644
--- a/toonz/sources/toonz/exportlevelpopup.cpp
+++ b/toonz/sources/toonz/exportlevelpopup.cpp
@@ -119,10 +119,10 @@ public:
 	TImageP &image() { return m_img; }
 
 protected:
-	void showEvent(QShowEvent *se);
-	void keyPressEvent(QKeyEvent *ke);
+	void showEvent(QShowEvent *se) override;
+	void keyPressEvent(QKeyEvent *ke) override;
 	void keyPressEvent(QShowEvent *se);
-	void paintGL();
+	void paintGL() override;
 
 	void setActualPixelSize();
 
diff --git a/toonz/sources/toonz/flipbook.cpp b/toonz/sources/toonz/flipbook.cpp
index 1e25c7b..db347be 100644
--- a/toonz/sources/toonz/flipbook.cpp
+++ b/toonz/sources/toonz/flipbook.cpp
@@ -1887,14 +1887,14 @@ void FlipBook::reset()
 void FlipBook::showEvent(QShowEvent *e)
 {
 	TSceneHandle *sceneHandle = TApp::instance()->getCurrentScene();
-	connect(sceneHandle, SIGNAL(sceneChanged()), m_imageViewer, SLOT(updateGL()));
+	connect(sceneHandle, SIGNAL(sceneChanged()), m_imageViewer, SLOT(update()));
 	// for updating the blank frame button
 	if (!m_imageViewer->isColorModel()) {
 		connect(sceneHandle, SIGNAL(preferenceChanged()), m_flipConsole, SLOT(onPreferenceChanged()));
 		m_flipConsole->onPreferenceChanged();
 	}
 	m_flipConsole->setActive(true);
-	m_imageViewer->updateGL();
+	m_imageViewer->update();
 }
 
 //-------------------------------------------------------------------
@@ -1902,7 +1902,7 @@ void FlipBook::showEvent(QShowEvent *e)
 void FlipBook::hideEvent(QHideEvent *e)
 {
 	TSceneHandle *sceneHandle = TApp::instance()->getCurrentScene();
-	disconnect(sceneHandle, SIGNAL(sceneChanged()), m_imageViewer, SLOT(updateGL()));
+	disconnect(sceneHandle, SIGNAL(sceneChanged()), m_imageViewer, SLOT(update()));
 	m_flipConsole->setActive(false);
 }
 
diff --git a/toonz/sources/toonz/imageviewer.cpp b/toonz/sources/toonz/imageviewer.cpp
index 68220de..693eb58 100644
--- a/toonz/sources/toonz/imageviewer.cpp
+++ b/toonz/sources/toonz/imageviewer.cpp
@@ -189,7 +189,7 @@ public:
 /*! \class ImageViewer
 		\brief The ImageViewer class provides to view an image.
 
-		Inherits \b QGLWidget.
+		Inherits \b QOpenGLWidget.
 
 		The object allows also to manage pan and zoom event. It's possible to set a
 		color mask TRop::ColorMask to image view.
@@ -205,10 +205,22 @@ public:
 */
 
 ImageViewer::ImageViewer(QWidget *parent, FlipBook *flipbook, bool showHistogram)
-	: QGLWidget(parent), m_pressedMousePos(0, 0), m_mouseButton(Qt::NoButton), m_draggingZoomSelection(false), m_image(), m_FPS(0), m_viewAff(), m_pos(0, 0), m_visualSettings(), m_compareSettings(), m_isHistogramEnable(showHistogram), m_flipbook(flipbook), m_isColorModel(false), m_histogramPopup(0), m_isRemakingPreviewFx(false)
-	  //, m_ghibli3DLutUtil(0) //iwsw commented out temporarily
-	  ,
-	  m_rectRGBPick(false)
+	: QOpenGLWidget(parent)
+	, m_pressedMousePos(0, 0)
+	, m_mouseButton(Qt::NoButton)
+	, m_draggingZoomSelection(false)
+	, m_image()
+	, m_FPS(0)
+	, m_viewAff()
+	, m_pos(0, 0)
+	, m_visualSettings()
+	, m_compareSettings()
+	, m_isHistogramEnable(showHistogram)
+	, m_flipbook(flipbook)
+	, m_isColorModel(false)
+	, m_histogramPopup(0)
+	, m_isRemakingPreviewFx(false)
+	, m_rectRGBPick(false)
 {
 	m_visualSettings.m_sceneProperties = TApp::instance()->getCurrentScene()->getScene()->getProperties();
 	m_visualSettings.m_drawExternalBG = true;
@@ -327,7 +339,7 @@ void ImageViewer::contextMenuEvent(QContextMenuEvent *event)
 	action->setParent(0);
 
 	delete menu;
-	updateGL();
+	update();
 }
 
 //-----------------------------------------------------------------------------
@@ -1128,6 +1140,14 @@ void ImageViewer::adaptView(const QRect &geomRect)
 	adaptView(imgBounds, viewRect);
 }
 
+void ImageViewer::doSwapBuffers() {
+	glFlush();
+}
+
+void ImageViewer::changeSwapBehavior(bool enable) {
+	setUpdateBehavior(enable ? PartialUpdate : NoPartialUpdate);
+}
+
 //-----------------------------------------------------------------------------
 
 void ImageViewer::keyPressEvent(QKeyEvent *event)
diff --git a/toonz/sources/toonz/imageviewer.h b/toonz/sources/toonz/imageviewer.h
index f3c9b4f..43810b2 100644
--- a/toonz/sources/toonz/imageviewer.h
+++ b/toonz/sources/toonz/imageviewer.h
@@ -8,7 +8,7 @@
 
 #include "toonz/imagepainter.h"
 
-#include <QGLWidget>
+#include <QOpenGLWidget>
 
 //-----------------------------------------------------------------------------
 
@@ -22,7 +22,7 @@ class HistogramPopup;
 //    ImageViewer
 //--------------------
 
-class ImageViewer : public QGLWidget
+class ImageViewer : public QOpenGLWidget
 {
 	Q_OBJECT
 	enum DragType { eNone,
@@ -106,12 +106,8 @@ public:
 	void adaptView(const TRect &imgRect, const TRect &viewRect);
 	void adaptView(const QRect &viewerRect);
 
-	void doSwapBuffers()
-	{
-		swapBuffers();
-		glFlush();
-	}
-	void changeSwapBehavior(bool enable) { setAutoBufferSwap(enable); }
+	void doSwapBuffers();
+	void changeSwapBehavior(bool enable);
 
 	//iwsw commented out temporarily
 	//Ghibli3DLutUtil* get3DLutUtil(){ return m_ghibli3DLutUtil; }
diff --git a/toonz/sources/toonz/linesfadepopup.cpp b/toonz/sources/toonz/linesfadepopup.cpp
index 85702ef..53b326c 100644
--- a/toonz/sources/toonz/linesfadepopup.cpp
+++ b/toonz/sources/toonz/linesfadepopup.cpp
@@ -107,7 +107,7 @@ public:
 	TRasterP raster() const { return m_ras; }
 	TRasterP &raster() { return m_ras; }
 
-	void paintGL()
+	void paintGL() override
 	{
 		drawBackground();
 
diff --git a/toonz/sources/toonz/linetestcapturepane.h b/toonz/sources/toonz/linetestcapturepane.h
index e1be964..986d3d0 100644
--- a/toonz/sources/toonz/linetestcapturepane.h
+++ b/toonz/sources/toonz/linetestcapturepane.h
@@ -15,7 +15,6 @@
 #include "toonzqt/checkbox.h"
 #include "toonzqt/colorfield.h"
 
-#include <QGLWidget>
 #include <QApplication>
 #include <QMainWindow>
 #include <QDialog>
diff --git a/toonz/sources/toonz/linetestviewer.cpp b/toonz/sources/toonz/linetestviewer.cpp
index 713849a..a364aba 100644
--- a/toonz/sources/toonz/linetestviewer.cpp
+++ b/toonz/sources/toonz/linetestviewer.cpp
@@ -129,7 +129,7 @@ LineTestViewer::LineTestViewer(QWidget *parent)
 #ifdef USE_QPAINTER
 	: QWidget(parent)
 #else
-	: QGLWidget(parent)
+	: QOpenGLWidget(parent)
 //, m_pboSupported(false)
 #endif //USE_QPAINTER
 	  ,
diff --git a/toonz/sources/toonz/linetestviewer.h b/toonz/sources/toonz/linetestviewer.h
index dbc57f2..c53c468 100644
--- a/toonz/sources/toonz/linetestviewer.h
+++ b/toonz/sources/toonz/linetestviewer.h
@@ -15,7 +15,7 @@
 #ifdef USE_QPAINTER
 #include <QWidget>
 #else
-#include <QGLWidget>
+#include <QOpenGLWidget>
 #endif
 
 //-----------------------------------------------------------------------------
@@ -25,7 +25,7 @@
 #ifdef USE_QPAINTER
 class LineTestViewer : public QWidget
 #else
-class LineTestViewer : public QGLWidget
+class LineTestViewer : public QOpenGLWidget
 #endif
 {
 	Q_OBJECT
diff --git a/toonz/sources/toonz/meshifypopup.cpp b/toonz/sources/toonz/meshifypopup.cpp
index a08e018..f26cf9c 100644
--- a/toonz/sources/toonz/meshifypopup.cpp
+++ b/toonz/sources/toonz/meshifypopup.cpp
@@ -514,7 +514,7 @@ public:
 		m_img = TImageP(), m_xsh = TXsheetP(), m_row = -1, m_meshImg = TMeshImageP();
 	}
 
-	void paintGL()
+	void paintGL() override
 	{
 		drawBackground();
 
diff --git a/toonz/sources/toonz/sceneviewer.cpp b/toonz/sources/toonz/sceneviewer.cpp
index cc48478..6bbad84 100644
--- a/toonz/sources/toonz/sceneviewer.cpp
+++ b/toonz/sources/toonz/sceneviewer.cpp
@@ -548,7 +548,7 @@ void SceneViewer::setVisual(const ImagePainter::VisualSettings &settings)
 	m_visualSettings = settings;
 	m_visualSettings.m_sceneProperties = TApp::instance()->getCurrentScene()->getScene()->getProperties();
 	if (repaint)
-		updateGL();
+		update();
 }
 
 //-----------------------------------------------------------------------------
diff --git a/toonz/sources/toonz/vectorizerswatch.h b/toonz/sources/toonz/vectorizerswatch.h
index 7413e7c..c8e79dd 100644
--- a/toonz/sources/toonz/vectorizerswatch.h
+++ b/toonz/sources/toonz/vectorizerswatch.h
@@ -79,8 +79,8 @@ public:
 	void setDrawInProgress(bool draw) { m_drawInProgress = draw; }
 
 protected:
-	bool event(QEvent *e);
-	void paintGL();
+	bool event(QEvent *e) override;
+	void paintGL() override;
 	void drawVectors();
 	void drawInProgress();
 };
diff --git a/toonz/sources/toonzlib/imagebuilders.cpp b/toonz/sources/toonzlib/imagebuilders.cpp
index 10c1a93..7431ea7 100644
--- a/toonz/sources/toonzlib/imagebuilders.cpp
+++ b/toonz/sources/toonzlib/imagebuilders.cpp
@@ -275,14 +275,6 @@ TImageP ImageRasterizer::build(int imFlags, void *extData)
 				QSurfaceFormat format;
 				format.setProfile(QSurfaceFormat::CompatibilityProfile);
 
-				std::unique_ptr<QOffscreenSurface> surface(new QOffscreenSurface());
-				surface->setFormat(format);
-				surface->create();
-
-				std::unique_ptr<QOpenGLContext> context(new QOpenGLContext());
-				context->create();
-				context->makeCurrent(surface.get());
-
 				TRaster32P ras(d);
 
 				glPushAttrib(GL_ALL_ATTRIB_BITS);
@@ -331,7 +323,6 @@ TImageP ImageRasterizer::build(int imFlags, void *extData)
 
 				glPopAttrib();
 
-				context->doneCurrent();
 				tglMakeCurrent(oldContext);
 
 				TRasterImageP ri = TRasterImageP(ras);
diff --git a/toonz/sources/toonzqt/pickrgbutils.cpp b/toonz/sources/toonzqt/pickrgbutils.cpp
index d8b95da..27f2fe4 100644
--- a/toonz/sources/toonzqt/pickrgbutils.cpp
+++ b/toonz/sources/toonzqt/pickrgbutils.cpp
@@ -5,7 +5,7 @@
 //Qt includes
 #include <QPixmap>
 #include <QImage>
-#include <QGLWidget>
+#include <QOpenGLWidget>
 #include <QDesktopWidget>
 #include <QApplication>
 
@@ -91,7 +91,7 @@ QRgb pickScreenRGB(const QRect &rect)
 
 //------------------------------------------------------------------------------
 
-QRgb pickRGB(QGLWidget *widget, const QRect &rect)
+QRgb pickRGB(QOpenGLWidget *widget, const QRect &rect)
 {
 	widget->makeCurrent();
 
diff --git a/toonz/sources/toonzqt/planeviewer.cpp b/toonz/sources/toonzqt/planeviewer.cpp
index c8ff3a6..c2a90a7 100644
--- a/toonz/sources/toonzqt/planeviewer.cpp
+++ b/toonz/sources/toonzqt/planeviewer.cpp
@@ -57,9 +57,12 @@ bool PlaneViewerZoomer::zoom(bool zoomin, bool resetZoom)
 //=========================================================================================
 
 PlaneViewer::PlaneViewer(QWidget *parent)
-	: QGLWidget(parent), m_firstResize(true), m_xpos(0), m_ypos(0), m_aff() // initialized at the first resize
-	  ,
-	  m_chessSize(40.0)
+	: QOpenGLWidget(parent)
+	, m_firstResize(true)
+	, m_xpos(0)
+	, m_ypos(0)
+	, m_aff() // initialized at the first resize
+	, m_chessSize(40.0)
 {
 	m_zoomRange[0] = 1e-3, m_zoomRange[1] = 1024.0;
 	setBgColor(TPixel32(235, 235, 235), TPixel32(235, 235, 235));
@@ -132,42 +135,38 @@ void PlaneViewer::drawBackground()
 
 //=========================================================================================
 
-//! The initMatrix() function is used to match the identity matrix with the widget reference,
-//! during widget size initialization.
-void PlaneViewer::initMatrix()
+void PlaneViewer::initializeGL()
 {
-	makeCurrent();
+}
+
+void PlaneViewer::resizeGL(int width, int height)
+{
+	glViewport(0, 0, width, height);
 
-	glViewport(0, 0, width(), height());
 	glMatrixMode(GL_PROJECTION);
 	glLoadIdentity();
-	gluOrtho2D(0, width(), 0, height());
+	gluOrtho2D(0, width, 0, height);
+
 	glMatrixMode(GL_MODELVIEW);
 	glLoadIdentity();
 
-	doneCurrent();
-}
-
-//=========================================================================================
-
-void PlaneViewer::resizeEvent(QResizeEvent *event)
-{
-	initMatrix();
-
-	const QSize &oldSize = event->oldSize(), &size = event->size();
-
 	if (m_firstResize) {
 		m_firstResize = false;
-		m_aff = TTranslation(0.5 * size.width(), 0.5 * size.height());
-	} else {
-		TPointD oldCenter(oldSize.width() * 0.5, oldSize.height() * 0.5);
-		TPointD newCenter(size.width() * 0.5, size.height() * 0.5);
+		m_aff = TTranslation(0.5 * width, 0.5 * height);
+		m_width = width;
+		m_height = height;
+	}
+	else {
+		TPointD oldCenter(m_width * 0.5, m_height * 0.5);
+		TPointD newCenter(width * 0.5, height * 0.5);
 
 		m_aff = m_aff.place(m_aff.inv() * oldCenter, newCenter);
+		m_width = width;
+		m_height = height;
 	}
 }
 
-//------------------------------------------------------
+//=========================================================================================
 
 void PlaneViewer::mouseMoveEvent(QMouseEvent *event)
 {
@@ -201,7 +200,7 @@ void PlaneViewer::keyPressEvent(QKeyEvent *event)
 	if (PlaneViewerZoomer(this).exec(event))
 		return;
 
-	QGLWidget::keyPressEvent(event);
+	QOpenGLWidget::keyPressEvent(event);
 }
 
 //------------------------------------------------------
diff --git a/toonz/sources/toonzqt/styleeditor.cpp b/toonz/sources/toonzqt/styleeditor.cpp
index 78eb933..731fbae 100644
--- a/toonz/sources/toonzqt/styleeditor.cpp
+++ b/toonz/sources/toonzqt/styleeditor.cpp
@@ -587,8 +587,8 @@ QPixmap makeSquareShading(
 //*****************************************************************************
 
 HexagonalColorWheel::HexagonalColorWheel(QWidget *parent)
-	: QGLWidget(parent), m_bgColor(128, 128, 128) //defaul value in case this value does not set in the style sheet
-												  //, m_ghibli3DLutUtil(0)//iwsw commented out temporarily
+	: QOpenGLWidget(parent)
+	, m_bgColor(128, 128, 128) //defaul value in case this value does not set in the style sheet
 {
 	setObjectName("HexagonalColorWheel");
 	setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
@@ -623,7 +623,8 @@ HexagonalColorWheel::~HexagonalColorWheel()
 
 void HexagonalColorWheel::initializeGL()
 {
-	qglClearColor(getBGColor());
+	QColor const color = getBGColor();
+	glClearColor(color.redF(), color.greenF(), color.blueF(), color.alphaF());
 
 	//iwsw commented out temporarily
 	/*
@@ -692,7 +693,8 @@ void HexagonalColorWheel::resizeGL(int width, int height)
 void HexagonalColorWheel::paintGL()
 {
 	//call ClearColor() here in order to update bg color when the stylesheet is switched
-	qglClearColor(getBGColor());
+	QColor const color = getBGColor();
+	glClearColor(color.redF(), color.greenF(), color.blueF(), color.alphaF());
 
 	glMatrixMode(GL_MODELVIEW);