What is set_animation_state for?

[paulrouget]

As far as I understand, there are 2 ways we want to run the embedder event loop.

Either Servo is not animating, then we block on window events, either Servo is animating, and then we block on swap_buffer.

If I'm not mistaken, this behavior was introduced a while back: c825592

But when animating, a Recomposite message i sent to the compositor. And sending any message to the compositor end up waking up the event loop (a Idle window event is generated). So blocking on window events works even during animations.

So, if my understand is right, it means that either:

• the embedder doesn't need to know about the animation state of Servo, and we should remove the set_animation_state callback
• servo should not bother waking up the compositor thread during animation and let embedder schedule that based on the animation state

@gw3583 you worked on that. Can you help me understand what we are supposed to do while animations are running?

[gw3583]

I can't recall the specifics, sorry. I think the main issue is probably that if the compositor thread is going to sleep / being woken up during animation, it's quite likely that it will miss vsync due to OS scheduler timing differences. This would result in animation sometimes looking janky if that occurs?

[paulrouget]

@gw3583 is it also possible that waking up the compositor thread too often might increase CPU consumption too?

[paulrouget]

I can measure that.

[asajeffrey]

Related: #22926.