# ---------------------------------------------------------------------------- # pyglet # Copyright (c) 2006-2008 Alex Holkner # Copyright (c) 2008-2023 pyglet contributors # All rights reserved. # # Redistribution and use in source and binary forms, with or without # modification, are permitted provided that the following conditions # are met: # # * Redistributions of source code must retain the above copyright # notice, this list of conditions and the following disclaimer. # * Redistributions in binary form must reproduce the above copyright # notice, this list of conditions and the following disclaimer in # the documentation and/or other materials provided with the # distribution. # * Neither the name of pyglet nor the names of its # contributors may be used to endorse or promote products # derived from this software without specific prior written # permission. # # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS # FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE # COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, # BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; # LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER # CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE # POSSIBILITY OF SUCH DAMAGE. # ---------------------------------------------------------------------------- """Event dispatch framework. All objects that produce events in pyglet implement :py:class:`~pyglet.event.EventDispatcher`, providing a consistent interface for registering and manipulating event handlers. A commonly used event dispatcher is `pyglet.window.Window`. Event types =========== For each event dispatcher there is a set of events that it dispatches; these correspond with the type of event handlers you can attach. Event types are identified by their name, for example, ''on_resize''. If you are creating a new class which implements :py:class:`~pyglet.event.EventDispatcher`, you must call `EventDispatcher.register_event_type` for each event type. Attaching event handlers ======================== An event handler is simply a function or method. You can attach an event handler by setting the appropriate function on the instance:: def on_resize(width, height): # ... dispatcher.on_resize = on_resize There is also a convenience decorator that reduces typing:: @dispatcher.event def on_resize(width, height): # ... You may prefer to subclass and override the event handlers instead:: class MyDispatcher(DispatcherClass): def on_resize(self, width, height): # ... Event handler stack =================== When attaching an event handler to a dispatcher using the above methods, it replaces any existing handler (causing the original handler to no longer be called). Each dispatcher maintains a stack of event handlers, allowing you to insert an event handler "above" the existing one rather than replacing it. There are two main use cases for "pushing" event handlers: * Temporarily intercepting the events coming from the dispatcher by pushing a custom set of handlers onto the dispatcher, then later "popping" them all off at once. * Creating "chains" of event handlers, where the event propagates from the top-most (most recently added) handler to the bottom, until a handler takes care of it. Use `EventDispatcher.push_handlers` to create a new level in the stack and attach handlers to it. You can push several handlers at once:: dispatcher.push_handlers(on_resize, on_key_press) If your function handlers have different names to the events they handle, use keyword arguments:: dispatcher.push_handlers(on_resize=my_resize, on_key_press=my_key_press) After an event handler has processed an event, it is passed on to the next-lowest event handler, unless the handler returns `EVENT_HANDLED`, which prevents further propagation. To remove all handlers on the top stack level, use `EventDispatcher.pop_handlers`. Note that any handlers pushed onto the stack have precedence over the handlers set directly on the instance (for example, using the methods described in the previous section), regardless of when they were set. For example, handler ``foo`` is called before handler ``bar`` in the following example:: dispatcher.push_handlers(on_resize=foo) dispatcher.on_resize = bar Dispatching events ================== pyglet uses a single-threaded model for all application code. Event handlers are only ever invoked as a result of calling EventDispatcher.dispatch_events`. It is up to the specific event dispatcher to queue relevant events until they can be dispatched, at which point the handlers are called in the order the events were originally generated. This implies that your application runs with a main loop that continuously updates the application state and checks for new events:: while True: dispatcher.dispatch_events() # ... additional per-frame processing Not all event dispatchers require the call to ``dispatch_events``; check with the particular class documentation. .. note:: In order to prevent issues with garbage collection, the :py:class:`~pyglet.event.EventDispatcher` class only holds weak references to pushed event handlers. That means the following example will not work, because the pushed object will fall out of scope and be collected:: dispatcher.push_handlers(MyHandlerClass()) Instead, you must make sure to keep a reference to the object before pushing it. For example:: my_handler_instance = MyHandlerClass() dispatcher.push_handlers(my_handler_instance) """ import inspect from functools import partial from weakref import WeakMethod EVENT_HANDLED = True EVENT_UNHANDLED = None class EventException(Exception): """An exception raised when an event handler could not be attached. """ pass class EventDispatcher: """Generic event dispatcher interface. See the module docstring for usage. """ # Placeholder empty stack; real stack is created only if needed _event_stack = () @classmethod def register_event_type(cls, name): """Register an event type with the dispatcher. Registering event types allows the dispatcher to validate event handler names as they are attached, and to search attached objects for suitable handlers. :Parameters: `name` : str Name of the event to register. """ if not hasattr(cls, 'event_types'): cls.event_types = [] cls.event_types.append(name) return name def push_handlers(self, *args, **kwargs): """Push a level onto the top of the handler stack, then attach zero or more event handlers. If keyword arguments are given, they name the event type to attach. Otherwise, a callable's `__name__` attribute will be used. Any other object may also be specified, in which case it will be searched for callables with event names. """ # Create event stack if necessary if type(self._event_stack) is tuple: self._event_stack = [] # Place dict full of new handlers at beginning of stack self._event_stack.insert(0, {}) self.set_handlers(*args, **kwargs) def _get_handlers(self, args, kwargs): """Implement handler matching on arguments for set_handlers and remove_handlers. """ for obj in args: if inspect.isroutine(obj): # Single magically named function name = obj.__name__ if name not in self.event_types: raise EventException('Unknown event "%s"' % name) if inspect.ismethod(obj): yield name, WeakMethod(obj, partial(self._remove_handler, name)) else: yield name, obj else: # Single instance with magically named methods for name in dir(obj): if name in self.event_types: meth = getattr(obj, name) yield name, WeakMethod(meth, partial(self._remove_handler, name)) for name, handler in kwargs.items(): # Function for handling given event (no magic) if name not in self.event_types: raise EventException('Unknown event "%s"' % name) if inspect.ismethod(handler): yield name, WeakMethod(handler, partial(self._remove_handler, name)) else: yield name, handler def set_handlers(self, *args, **kwargs): """Attach one or more event handlers to the top level of the handler stack. See :py:meth:`~pyglet.event.EventDispatcher.push_handlers` for the accepted argument types. """ # Create event stack if necessary if type(self._event_stack) is tuple: self._event_stack = [{}] for name, handler in self._get_handlers(args, kwargs): self.set_handler(name, handler) def set_handler(self, name, handler): """Attach a single event handler. :Parameters: `name` : str Name of the event type to attach to. `handler` : callable Event handler to attach. """ # Create event stack if necessary if type(self._event_stack) is tuple: self._event_stack = [{}] self._event_stack[0][name] = handler def pop_handlers(self): """Pop the top level of event handlers off the stack. """ assert self._event_stack and 'No handlers pushed' del self._event_stack[0] def remove_handlers(self, *args, **kwargs): """Remove event handlers from the event stack. See :py:meth:`~pyglet.event.EventDispatcher.push_handlers` for the accepted argument types. All handlers are removed from the first stack frame that contains any of the given handlers. No error is raised if any handler does not appear in that frame, or if no stack frame contains any of the given handlers. If the stack frame is empty after removing the handlers, it is removed from the stack. Note that this interferes with the expected symmetry of :py:meth:`~pyglet.event.EventDispatcher.push_handlers` and :py:meth:`~pyglet.event.EventDispatcher.pop_handlers`. """ handlers = list(self._get_handlers(args, kwargs)) # Find the first stack frame containing any of the handlers def find_frame(): for frame in self._event_stack: for name, handler in handlers: try: if frame[name] == handler: return frame except KeyError: pass frame = find_frame() # No frame matched; no error. if not frame: return # Remove each handler from the frame. for name, handler in handlers: try: if frame[name] == handler: del frame[name] except KeyError: pass # Remove the frame if it's empty. if not frame: self._event_stack.remove(frame) def remove_handler(self, name, handler): """Remove a single event handler. The given event handler is removed from the first handler stack frame it appears in. The handler must be the exact same callable as passed to `set_handler`, `set_handlers` or :py:meth:`~pyglet.event.EventDispatcher.push_handlers`; and the name must match the event type it is bound to. No error is raised if the event handler is not set. :Parameters: `name` : str Name of the event type to remove. `handler` : callable Event handler to remove. """ for frame in self._event_stack: try: if frame[name] == handler: del frame[name] break except KeyError: pass def _remove_handler(self, name, handler): """Used internally to remove all handler instances for the given event name. This is normally called from a dead ``WeakMethod`` to remove itself from the event stack. """ # Iterate over a copy as we might mutate the list for frame in list(self._event_stack): if name in frame and frame[name] == handler: del frame[name] if not frame: self._event_stack.remove(frame) def dispatch_event(self, event_type, *args): """Dispatch a single event to the attached handlers. The event is propagated to all handlers from from the top of the stack until one returns `EVENT_HANDLED`. This method should be used only by :py:class:`~pyglet.event.EventDispatcher` implementors; applications should call the ``dispatch_events`` method. Since pyglet 1.2, the method returns `EVENT_HANDLED` if an event handler returned `EVENT_HANDLED` or `EVENT_UNHANDLED` if all events returned `EVENT_UNHANDLED`. If no matching event handlers are in the stack, ``False`` is returned. :Parameters: `event_type` : str Name of the event. `args` : sequence Arguments to pass to the event handler. :rtype: bool or None :return: (Since pyglet 1.2) `EVENT_HANDLED` if an event handler returned `EVENT_HANDLED`; `EVENT_UNHANDLED` if one or more event handlers were invoked but returned only `EVENT_UNHANDLED`; otherwise ``False``. In pyglet 1.1 and earlier, the return value is always ``None``. """ assert hasattr(self, 'event_types'), ( "No events registered on this EventDispatcher. " "You need to register events with the class method " "EventDispatcher.register_event_type('event_name')." ) assert event_type in self.event_types, \ "%r not found in %r.event_types == %r" % (event_type, self, self.event_types) invoked = False # Search handler stack for matching event handlers for frame in list(self._event_stack): handler = frame.get(event_type, None) if not handler: continue if isinstance(handler, WeakMethod): handler = handler() assert handler is not None try: invoked = True if handler(*args): return EVENT_HANDLED except TypeError as exception: self._raise_dispatch_exception(event_type, args, handler, exception) # Check instance for an event handler try: if getattr(self, event_type)(*args): return EVENT_HANDLED except AttributeError as e: event_op = getattr(self, event_type, None) if callable(event_op): raise e except TypeError as exception: self._raise_dispatch_exception(event_type, args, getattr(self, event_type), exception) else: invoked = True if invoked: return EVENT_UNHANDLED return False @staticmethod def _raise_dispatch_exception(event_type, args, handler, exception): # A common problem in applications is having the wrong number of # arguments in an event handler. This is caught as a TypeError in # dispatch_event but the error message is obfuscated. # # Here we check if there is indeed a mismatch in argument count, # and construct a more useful exception message if so. If this method # doesn't find a problem with the number of arguments, the error # is re-raised as if we weren't here. n_args = len(args) # Inspect the handler argspecs = inspect.getfullargspec(handler) handler_args = argspecs.args handler_varargs = argspecs.varargs handler_defaults = argspecs.defaults n_handler_args = len(handler_args) # Remove "self" arg from handler if it's a bound method if inspect.ismethod(handler) and handler.__self__: n_handler_args -= 1 # Allow *args varargs to overspecify arguments if handler_varargs: n_handler_args = max(n_handler_args, n_args) # Allow default values to overspecify arguments if n_handler_args > n_args >= n_handler_args - len(handler_defaults) and handler_defaults: n_handler_args = n_args if n_handler_args != n_args: if inspect.isfunction(handler) or inspect.ismethod(handler): descr = f"'{handler.__name__}' at {handler.__code__.co_filename}:{handler.__code__.co_firstlineno}" else: descr = repr(handler) raise TypeError(f"The '{event_type}' event was dispatched with {len(args)} arguments,\n" f"but your handler {descr} accepts only {n_handler_args} arguments.") else: raise exception def event(self, *args): """Function decorator for an event handler. Usage:: win = window.Window() @win.event def on_resize(self, width, height): # ... or:: @win.event('on_resize') def foo(self, width, height): # ... """ if len(args) == 0: # @window.event() def decorator(func): func_name = func.__name__ self.set_handler(func_name, func) return func return decorator elif inspect.isroutine(args[0]): # @window.event func = args[0] name = func.__name__ self.set_handler(name, func) return args[0] elif isinstance(args[0], str): # @window.event('on_resize') name = args[0] def decorator(func): self.set_handler(name, func) return func return decorator