Add the ConstantRandom utility class

game/scripts/utility/common_functions.rpy

@@ -226,3 +226,33 @@ init python early:
         Returns the value returned by the screen, if any.
         """
         return renpy.call_in_new_context("call_screen", sc_name, *args, **kwargs)
+
+    class ConstantRandom(random.Random):
+        """
+        The state of the object never changes when generative methods are called,
+        meaning that successive calls of the same method with the same arguments
+        produce the same results.
+
+        Populated in the block below.
+        """
+
+        def seed(self, a=None, *args, **kwargs):
+            if a is None:
+                a = renpy.random.random()
+            super().seed(a, *args, **kwargs)
+            self.state = self.getstate()
+
+python early hide:
+    service_randomobj = random.Random()
+
+    def random_wrap(func_name):
+        def wrapped(self, *args, **kwargs):
+            service_randomobj.setstate(self.getstate())
+            rv = getattr(service_randomobj, func_name)(*args, **kwargs)
+            return rv
+        return wrapped
+
+    for fn in random.__all__:
+        if fn in ("Random", "SystemRandom", "getstate", "setstate", "seed"):
+            continue
+        setattr(ConstantRandom, fn, random_wrap(fn))