BF: adding a potential fix to the pyglet shadow_window issue

Some graphics cards (or their drivers) don't support OpenGL
shadow windows, which pyglet uses to bind textures etc. Turning it off
should only affect people that need multiple windows, with stimuli
shared between them.

psychopy/visual/window.py

@@ -1469,12 +1469,29 @@ def _setupPyglet(self):
             style = None
         else:
             style = 'borderless'
-        self.winHandle = pyglet.window.Window(width=w, height=h,
-                                              caption="PsychoPy",
-                                              fullscreen=self._isFullScr,
-                                              config=config,
-                                              screen=thisScreen,
-                                              style=style)
+        try:
+            self.winHandle = pyglet.window.Window(
+                    width=w, height=h,
+                    caption="PsychoPy",
+                    fullscreen=self._isFullScr,
+                    config=config,
+                    screen=thisScreen,
+                    style=style)
+        except pyglet.gl.ContextException:
+            # turn off the shadow window an try again
+            pyglet.options['shadow_window'] = False
+            self.winHandle = pyglet.window.Window(
+                    width=w, height=h,
+                    caption="PsychoPy",
+                    fullscreen=self._isFullScr,
+                    config=config,
+                    screen=thisScreen,
+                    style=style)
+            logging.warning("Pyglet shadow_window has been turned off. This is "
+                            "only an issue for you if you need multiple "
+                            "stimulus windows, in which case update your "
+                            "graphics card and/or graphics drivers.")
+
         if sys.platform == 'win32':
             # pyHook window hwnd maps to:
             # pyglet 1.14 -> window._hwnd