Fix python event routing sender mismatch for playhead events

[richardssam]

• Resolve issue where playhead events (position_atom, etc.) were silently dropped in the Python API. When C++ event groups broadcast messages, the sender is set to the owner actor (e.g. Playhead) rather than the event group address.
• Add support for mapping callback IDs to an optional owner actor address in EventToPythonThreadLockerActor.
• Update subscribe_to_playhead_events in plugin_base.py and subscribe_to_event_group in module.py to pass the owner actor as the third argument to add_message_callback.

I have to be honest, this is code from gemini, I was trying to use the event system as much as I could, so tried using the playhead, but ran into problems getting the information from it, so if there is a better way to get playhead events to python let me know.

[tedwaine]

Hi @richardssam

Thanks for this. I tried it out but there were still problems as the events emitted by a playhead contain data types that aren't compatible with python. Nice try Gemini.

I have instead modified the python PluginBase class (in my recent commit). You can simply call 'self.subscribe_to_playhead_events()' in your plugin code. You also need to override playhead_attribute_changed and onscreen_media_changed methods in your plugin - you will then get pretty granular updates on the playhead state via those methods.