diff --git a/pyqtgraph/opengl/GLGraphicsItem.py b/pyqtgraph/opengl/GLGraphicsItem.py
index a2c2708a..bf9de81a 100644
--- a/pyqtgraph/opengl/GLGraphicsItem.py
+++ b/pyqtgraph/opengl/GLGraphicsItem.py
@@ -1,8 +1,7 @@
 from OpenGL.GL import *
 from OpenGL import GL
-from ..Qt import QtGui, QtCore
+from ..Qt import QtCore
 from .. import Transform3D
-from ..python2_3 import basestring
 
 
 GLOptions = {
@@ -42,6 +41,7 @@ class GLGraphicsItem(QtCore.QObject):
         self.__children = set()
         self.__transform = Transform3D()
         self.__visible = True
+        self.__initialized = False
         self.setParentItem(parentItem)
         self.setDepthValue(0)
         self.__glOpts = {}
@@ -91,7 +91,7 @@ class GLGraphicsItem(QtCore.QObject):
             
         
         """
-        if isinstance(opts, basestring):
+        if isinstance(opts, str):
             opts = GLOptions[opts]
         self.__glOpts = opts.copy()
         self.update()
@@ -228,6 +228,11 @@ class GLGraphicsItem(QtCore.QObject):
         view, as it may be obscured or outside of the current view area."""
         return self.__visible
     
+    def setInitialized(self, init=True):
+        self.__initialized = init
+
+    def initialized(self):
+        return self.__initialized
     
     def initializeGL(self):
         """
@@ -235,7 +240,7 @@ class GLGraphicsItem(QtCore.QObject):
         The widget's GL context is made current before this method is called.
         (So this would be an appropriate time to generate lists, upload textures, etc.)
         """
-        pass
+        self.setInitialized()
     
     def setupGLState(self):
         """
@@ -245,7 +250,7 @@ class GLGraphicsItem(QtCore.QObject):
         for k,v in self.__glOpts.items():
             if v is None:
                 continue
-            if isinstance(k, basestring):
+            if isinstance(k, str):
                 func = getattr(GL, k)
                 func(*v)
             else:
diff --git a/pyqtgraph/opengl/GLViewWidget.py b/pyqtgraph/opengl/GLViewWidget.py
index 8896bdc0..61a7d445 100644
--- a/pyqtgraph/opengl/GLViewWidget.py
+++ b/pyqtgraph/opengl/GLViewWidget.py
@@ -8,7 +8,6 @@ import warnings
 from math import cos, sin, tan, radians
 ##Vector = QtGui.QVector3D
 
-ShareWidget = None
 
 class GLViewWidget(QtWidgets.QOpenGLWidget):
     
@@ -99,10 +98,12 @@ class GLViewWidget(QtWidgets.QOpenGLWidget):
 
     def addItem(self, item):
         self.items.append(item)
-        if hasattr(item, 'initializeGL'):
+
+        if self.isValid():
             self.makeCurrent()
             try:
                 item.initializeGL()
+                item.setInitialized()
             except:
                 self.checkOpenGLVersion('Error while adding item %s to GLViewWidget.' % str(item))
                 
@@ -128,7 +129,10 @@ class GLViewWidget(QtWidgets.QOpenGLWidget):
         self.update()        
         
     def initializeGL(self):
-        self.resizeGL(self.width(), self.height())
+        for item in self.items:
+            if not item.initialized():
+                item.initializeGL()
+                item.setInitialized()
         
     def setBackgroundColor(self, *args, **kwds):
         """