[Webkit-unassigned] [Bug 70955] Add CCSmoothedCallback class for smoothing out jittery vsync

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=70955





--- Comment #13 from Iain Merrick <husky at google.com>  2011-11-02 04:28:58 PST ---
(In reply to comment #12)
> (From update of attachment 112877 [details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=112877&action=review
> 
> Have you verified if this behaves significantly better/differently from the timer based source?

Well, it locks phase with an external signal? CCDelayBasedTimeSource has no way of staying in phase.

Maybe CCSmoothedTimeSource should actually *use* CCDelayBasedTimeSource, or subclass it. But I'm not sure that would make the code simpler.

> > Source/WebCore/platform/graphics/chromium/cc/CCThread.h:51
> > +    // Get this thread's monotonically-increasing millisecond clock.
> 
> This doesn't make sense to me. the time is not a property of the thread.

It has to be a virtual somewhere for testability, and it's significantly simpler to have it here than elsewhere. For example, if it's a virtual in each class that calls monotonicallyIncreasingTime(), each of those classes needs its own subclass for testing. If it's an overridable global function, tests will interfere with each other.

I agree it looks a bit odd here, but I think it's somewhat justifiable, as the thread already has postDelayedTask() which uses the same units. postDelayedTask() and monotonicallyIncreasingTime() are closely related and frequently used together.

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