Kill the tractor tree on window close.

This makes it so you don't have to ctrl-c kill apps.
Add in the experimental openGL support even though I'm pretty sure it's
not being used much for curve plotting (but could be wrong).

piker/ui/_exec.py

@@ -26,6 +26,7 @@ from typing import Tuple, Callable, Dict, Any
 
 # Qt specific
 import PyQt5  # noqa
+import pyqtgraph as pg
 from pyqtgraph import QtGui
 from PyQt5 import QtCore
 from PyQt5.QtCore import (
@@ -37,6 +38,12 @@ import tractor
 from outcome import Error
 
 
+# pyqtgraph global config
+# might as well enable this for now?
+pg.useOpenGL = True
+pg.enableExperimental = True
+
+
 # singleton app per actor
 _qt_app: QtGui.QApplication = None
 _qt_win: QtGui.QMainWindow = None
@@ -67,6 +74,12 @@ class MainWindow(QtGui.QMainWindow):
         self.setMinimumSize(*self.size)
         self.setWindowTitle(self.title)
 
+    def closeEvent(self, event: 'QCloseEvent') -> None:
+        """Cancel the root actor asap.
+
+        """
+        tractor.current_actor().cancel_soon()
+
 
 def run_qtractor(
     func: Callable,
@@ -131,6 +144,9 @@ def run_qtractor(
     instance = main_widget()
     instance.window = window
 
+    # kill the app when root actor terminates
+    tractor._actor._lifetime_stack.callback(app.quit)
+
     widgets = {
         'window': window,
         'main': instance,