pythonarcade
Document event order when using views (on_draw, on_update)
Enhancement request:
Make Window and View's on_draw() call self.clear() instead of pass.
What should be added/changed?
See above 😅
It's possible this only makes sense to do for Window and not View, as @einarf points out here:
What I'm not sure about right now is how the
on_draw/on_updateevents work with views. As far as I remember both the window and view methods can be called in a frame. That in turn can case games to clear the window twice
What would it help with?
Since on_draw() is likely to be overriden anyway, this gives a resonable default in which it doesn't appear like methods like arcade.set_background_color() (which require a screen to be cleared to have noticeable effect) do anything.
We have to look into how on_draw / on_update events trigger. It can run for both the view and the window. You can return return pyglet.event.EVENT_HANDLED from these to ensure the window methods is not called I think, but this is not something we have exposed in arcade.
From my understanding, both the window's on_draw and the view's on_draw are called. Annoyingly the view's on_draw is called first.
This is also true for update and on_update. the call order is view's update, window's update, view's on_update, and finally window's on_update.
You would need a special Window only event called "begin_draw" or something.
Changed this into a documentation task.
Pyglet is using a stack to dispatch event. When you activate a view all the on_ methods for the view will be called since its on the top os the stack. Then the window events are triggered.
To avoid the window on_draw to be called the View's on_draw needs to return True to signal to the event dispacher that the event is handled.
Im looking into making the order of the draws and updates more consistent. With proper documentation and the like.