From e9ec5e0c93d4fa4787cb4f7501775f7995e1845e Mon Sep 17 00:00:00 2001
From: Sahil Makhijani <sahil.makhijani@gmail.com>
Date: Tue, 2 Feb 2021 15:59:27 +0530
Subject: [PATCH] Added Concept of Event Listners and Event Dispatcher

---
 manimlib/event/__init__.py         |  6 ++
 manimlib/event/event_dispatcher.py | 92 ++++++++++++++++++++++++++++++
 manimlib/event/event_listner.py    | 15 +++++
 manimlib/event/event_type.py       | 11 ++++
 4 files changed, 124 insertions(+)
 create mode 100644 manimlib/event/__init__.py
 create mode 100644 manimlib/event/event_dispatcher.py
 create mode 100644 manimlib/event/event_listner.py
 create mode 100644 manimlib/event/event_type.py

diff --git a/manimlib/event/__init__.py b/manimlib/event/__init__.py
new file mode 100644
index 00000000..2702617b
--- /dev/null
+++ b/manimlib/event/__init__.py
@@ -0,0 +1,6 @@
+from manimlib.event.event_dispatcher import EventDispatcher
+
+
+# This is supposed to be a Singleton
+# i.e., during runtime there should be only one object of Event Dispatcher
+EVENT_DISPATCHER = EventDispatcher()
diff --git a/manimlib/event/event_dispatcher.py b/manimlib/event/event_dispatcher.py
new file mode 100644
index 00000000..2d6cddad
--- /dev/null
+++ b/manimlib/event/event_dispatcher.py
@@ -0,0 +1,92 @@
+import numpy as np
+
+from manimlib.event.event_type import EventType
+from manimlib.event.event_listner import EventListner
+
+
+class EventDispatcher(object):
+    def __init__(self):
+        self.event_listners = {
+            event_type: []
+            for event_type in EventType
+        }
+        self.mouse_point = np.array((0., 0., 0.))
+        self.mouse_drag_point = np.array((0., 0., 0.))
+        self.pressed_keys = set()
+        self.draggable_object_listners = []
+
+    def add_listner(self, event_listner):
+        assert(isinstance(event_listner, EventListner))
+        self.event_listners[event_listner.event_type].append(event_listner)
+        return self
+
+    def remove_listner(self, event_listner):
+        assert(isinstance(event_listner, EventListner))
+        try:
+            while event_listner in self.event_listners[event_listner.event_type]:
+                self.event_listners[event_listner.event_type].remove(event_listner)
+        except:
+            # raise ValueError("Handler is not handling this event, so cannot remove it.")
+            pass
+        return self
+
+    def dispatch(self, event_type, **event_data):
+
+        if event_type == EventType.MouseMotionEvent:
+            self.mouse_point = event_data["point"]
+        elif event_type == EventType.MouseDragEvent:
+            self.mouse_drag_point = event_data["point"]
+        elif event_type == EventType.KeyPressEvent:
+            self.pressed_keys.add(event_data["symbol"])  # Modifiers?
+        elif event_type == EventType.KeyReleaseEvent:
+            self.pressed_keys.difference_update({event_data["symbol"]})  # Modifiers?
+        elif event_type == EventType.MousePressEvent:
+            self.draggable_object_listners = [
+                listner
+                for listner in self.event_listners[EventType.MouseDragEvent]
+                if listner.mobject.is_point_touching(self.mouse_point)
+            ]
+        elif event_type == EventType.MouseReleaseEvent:
+            self.draggable_object_listners = []
+
+        propagate_event = None
+
+        if event_type == EventType.MouseDragEvent:
+            for listner in self.draggable_object_listners:
+                assert(isinstance(listner, EventListner))
+                propagate_event = listner.callback(listner.mobject, event_data)
+                if propagate_event is not None and propagate_event is False:
+                    return propagate_event
+
+        elif event_type.value.startswith('mouse'):
+            for listner in self.event_listners[event_type]:
+                if listner.mobject.is_point_touching(self.mouse_point):
+                    propagate_event = listner.callback(
+                        listner.mobject, event_data)
+                    if propagate_event is not None and propagate_event is False:
+                        return propagate_event
+
+        elif event_type.value.startswith('key'):
+            for listner in self.event_listners[event_type]:
+                propagate_event = listner.callback(listner.mobject, event_data)
+                if propagate_event is not None and propagate_event is False:
+                    return propagate_event
+
+        return propagate_event
+
+    def get_listners_count(self):
+        return sum([len(value) for key, value in self.event_listners.items()])
+
+    def get_mouse_point(self):
+        return self.mouse_point
+
+    def get_mouse_drag_point(self):
+        return self.mouse_drag_point
+
+    def is_key_pressed(self, symbol):
+        return (symbol in self.pressed_keys)
+
+    __iadd__ = add_listner
+    __isub__ = remove_listner
+    __call__ = dispatch
+    __len__ = get_listners_count
diff --git a/manimlib/event/event_listner.py b/manimlib/event/event_listner.py
new file mode 100644
index 00000000..2f8663f7
--- /dev/null
+++ b/manimlib/event/event_listner.py
@@ -0,0 +1,15 @@
+class EventListner(object):
+    def __init__(self, mobject, event_type, event_callback):
+        self.mobject = mobject
+        self.event_type = event_type
+        self.callback = event_callback
+
+    def __eq__(self, o: object) -> bool:
+        return_val = False
+        try:
+            return_val = self.callback == o.callback \
+                and self.mobject == o.mobject \
+                and self.event_type == o.event_type
+        except:
+            pass
+        return return_val
diff --git a/manimlib/event/event_type.py b/manimlib/event/event_type.py
new file mode 100644
index 00000000..6cd9f73e
--- /dev/null
+++ b/manimlib/event/event_type.py
@@ -0,0 +1,11 @@
+from enum import Enum
+
+
+class EventType(Enum):
+    MouseMotionEvent = 'mouse_motion_event'
+    MousePressEvent = 'mouse_press_event'
+    MouseReleaseEvent = 'mouse_release_event'
+    MouseDragEvent = 'mouse_drag_event'
+    MouseScrollEvent = 'mouse_scroll_event'
+    KeyPressEvent = 'key_press_event'
+    KeyReleaseEvent = 'key_release_event'