Better feedback when getting window or context before creation

Author: einarf

demosys/context/__init__.py

@@ -6,9 +6,16 @@
 
 def window() -> 'demosys.context.base.Window':
     """The window instance we are rendering to"""
+    if not WINDOW:
+        raise RuntimeError("Attempting to get window before creation")
+
     return WINDOW
 
 
 def ctx() -> moderngl.Context:
     """ModernGL context"""
-    return WINDOW.ctx
+    win = window()
+    if not win.ctx:
+        raise RuntimeError("Attempting to get context before creation")
+
+    return win.ctx