Animations aren't started if there's no window events

[asajeffrey]

If a page with requestAnimationFrame is loaded, it doesn't start animating until a window event is generated. The reason why is that servo has two modes: AnimationState::Animating (which blocks on vsync when swapping the GL buffers) and AnimationState::Idle (which blocks on window events). The problem is that the transition from one to the other needs a window event to trigger it.

[asajeffrey]

Really we should select between a window event and a compositor event, but window events aren't arriving from an mpsc channel, so we can't select on them. We could spin up a routing thread that wakes up the window when a compositor event arrives?

[paulrouget]

When switching from Idle to Animating, isn't the compositor thread waken up via the EventLoopWaker? The embedder would then call perform_udpates which will then call WindowMethods::set_animation_state ?

[asajeffrey]

I don't think so, which thread does this?

[paulrouget]

The constellation is supposed to wake up the compositor thread.

The constellation is supposed to be getting a ChangeRunningAnimationsState message, and then send a message to the compositor via the compositor_proxy (which will make sure the compositor/embedder thread is woken up).

I'm wondering what is not working here.

[asajeffrey]

I think what's happening is that the compositor thread is blocked waiting for a window event, not a compositor event. Wouldn't the constellation have to generate a window event if it wants to wake up the compositor thread?

[paulrouget]

Wouldn't the constellation have to generate a window event if it wants to wake up the compositor thread?

Yes. It's exactly what it's supposed to happen. Via

servo/components/compositing/compositor_thread.rs

Line 28 in f180b84

impl CompositorProxy {

[asajeffrey]

Oh, you're right. OK, I don't understand what's going on then :/ I'll do a bit more digging, it's possible this is a problem with my code.

[paulrouget]

@asajeffrey is still happening?