Prevent UI events from propagating beyond imgui (#569)

* event propagation

* update

* fix remove event handler

wgpu/gui/base.py

@@ -197,7 +197,7 @@ def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self._last_event_time = 0
         self._pending_events = {}
-        self._event_handlers = defaultdict(set)
+        self._event_handlers = defaultdict(list)
 
     def _get_event_wait_time(self):
         """Calculate the time to wait for the next event dispatching.
@@ -274,18 +274,21 @@ def handle_event(self, event):
         """
         # Collect callbacks
         event_type = event.get("event_type")
-        callbacks = self._event_handlers[event_type] | self._event_handlers["*"]
+        callbacks = self._event_handlers[event_type] + self._event_handlers["*"]
         # Dispatch
-        for callback in callbacks:
+        for _, callback in callbacks:
             with log_exception(f"Error during handling {event['event_type']} event"):
+                if event.get("stop_propagation", False):
+                    break
                 callback(event)
 
-    def add_event_handler(self, *args):
+    def add_event_handler(self, *args, order=0):
         """Register an event handler to receive events.
 
         Arguments:
             callback (callable): The event handler. Must accept a single event argument.
             *types (list of strings): A list of event types.
+            order (int): The order in which the handler is called. Lower numbers are called first. Default is 0.
 
         For the available events, see
         https://jupyter-rfb.readthedocs.io/en/stable/events.html.
@@ -331,7 +334,8 @@ def my_handler(event):
 
         def decorator(_callback):
             for type in types:
-                self._event_handlers[type].add(_callback)
+                self._event_handlers[type].append((order, _callback))
+                self._event_handlers[type].sort(key=lambda x: x[0])
             return _callback
 
         if decorating:
@@ -346,4 +350,6 @@ def remove_event_handler(self, callback, *types):
             *types (list of strings): A list of event types.
         """
         for type in types:
-            self._event_handlers[type].remove(callback)
+            self._event_handlers[type] = [
+                (o, cb) for o, cb in self._event_handlers[type] if cb is not callback
+            ]

wgpu/utils/imgui/imgui_renderer.py

@@ -78,11 +78,13 @@ def __init__(
         self._backend.io.display_framebuffer_scale = (scale, scale)
 
         canvas.add_event_handler(self._on_resize, "resize")
-        canvas.add_event_handler(self._on_mouse_move, "pointer_move")
-        canvas.add_event_handler(self._on_mouse, "pointer_up", "pointer_down")
-        canvas.add_event_handler(self._on_key, "key_up", "key_down")
-        canvas.add_event_handler(self._on_wheel, "wheel")
-        canvas.add_event_handler(self._on_char_input, "char")
+        canvas.add_event_handler(self._on_mouse_move, "pointer_move", order=-99)
+        canvas.add_event_handler(
+            self._on_mouse, "pointer_up", "pointer_down", order=-99
+        )
+        canvas.add_event_handler(self._on_key, "key_up", "key_down", order=-99)
+        canvas.add_event_handler(self._on_wheel, "wheel", order=-99)
+        canvas.add_event_handler(self._on_char_input, "char", order=-99)
 
         self._update_gui_function = None
 
@@ -152,11 +154,17 @@ def _on_resize(self, event):
     def _on_mouse_move(self, event):
         self._backend.io.add_mouse_pos_event(event["x"], event["y"])
 
+        if self._backend.io.want_capture_mouse:
+            event["stop_propagation"] = True
+
     def _on_mouse(self, event):
         event_type = event["event_type"]
         down = event_type == "pointer_down"
         self._backend.io.add_mouse_button_event(event["button"] - 1, down)
 
+        if self._backend.io.want_capture_mouse:
+            event["stop_propagation"] = True
+
     def _on_key(self, event):
         event_type = event["event_type"]
         down = event_type == "key_down"
@@ -182,8 +190,17 @@ def _on_key(self, event):
             key = self.KEY_MAP_MOD[key_name]
             self._backend.io.add_key_event(key, down)
 
+        if self._backend.io.want_capture_keyboard:
+            event["stop_propagation"] = True
+
     def _on_wheel(self, event):
         self._backend.io.add_mouse_wheel_event(event["dx"] / 100, event["dy"] / 100)
 
+        if self._backend.io.want_capture_mouse:
+            event["stop_propagation"] = True
+
     def _on_char_input(self, event):
         self._backend.io.add_input_characters_utf8(event["char_str"])
+
+        if self._backend.io.want_text_input:
+            event["stop_propagation"] = True