[visionegg] Re: falling out of a go() loop which is set to run_forever so that a second go() loop can be allowed to run

Hi Mark,

I'm also wondering if there are timing (or other) issues in
organizing my stimulus presentation in this way (is it better to simply have
one main loop, rather than a number of loops in sequence)?

I don't think there are timing or other issues involved. I think its largely a matter of personal preference. For your task I think it might be conceptually cleaner to write your own main loop rather than using the Presentation class.

(When I first wrote the Vision Egg, I was using it mainly for electrophysiology experiments where the go loop paradigm is very useful. The ephys_server and GUI is built on that paradigm. But for psychophysics I think it's generally less useful.)

I'm still in the process of adding more demos that show use of your own main loop, and I think the ones that do exist are only in the bleeding edge release so far.

How do I quit prematurely out of a go() loop (say, as a result of a mouse
button press), without exiting the VisionEgg script entirely?

It is possible to do it this way, so here's the answer to your question:

If you have an instance of Presentation called p, setting p.parameters.go_duration = (0,'frames') would stop the go loop before drawing another frame.

So, your event handlers will have have a reference to the instance of Presentation you want to quit. Therefore, you might need to define your instances of Presentation as before, but then modify the event handler:

class ButtonDown:
        def set_presentation_instance(self, p):
                self.p = p
        def click(self, event):
                if event.button == 1:
                        self.p.parameters.go_duration = (0,'frames')

button_down = ButtonDown()

handle_event_callbacks = [(pygame.locals.QUIT, quit),
(pygame.locals.MOUSEBUTTONDOWN,button_down.click),
(pygame.locals.MOUSEBUTTONUP, mouse_button_up),
(pygame.locals.KEYDOWN, keydown)]

p = Presentation(go_duration=('forever',), viewports=[view],
        handle_event_callbacks=handle_event_callbacks)

q = ...
r = ...

button_down.set_presentation_instance(p)
p.go()
button_down.set_presentation_instance(q)
q.go()
button_down.set_presentation_instance(r)
r.go()

Something like that should do what you want. But, as I said, it may be cleaner to write your own control flow rather than resort to object oriented trickery like this.

Cheers!
Andrew

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