The following numbers are roughly as reported by the CPU meter of iStat Menus 100% is one core. I didn't see any significant difference in CPU usage between Firefox 52 ESR, FF 56.0.2, and FF 57.0b14 with or without Servo enabled. There are often several of them on one page, which can quickly add up to 100% CPU usage for tiny hidden animations, at least on a Mac. The test page shows some typical examples of the 'loading spinners' used on virtually every modern website, which are usually kept in a 'visibility: hidden' element when not being displayed. Details I was just testing this out on the Quantum beta on my Macbook, here are some rough results using the attached test page. HTML test page for hidden 'loading spinners'. Throttle animations if the flag is true and CanIgnoreIfNotVisible() is true.Ĭameron, does this solution sound feasible? Add a function to return the flag in nsStyleContext.ĥ. In nsStyleContext::ApplyStyleFixups(), check StyleVisibility()->IsVisible(), if it's true, then the flags of all ancestors are set to false.Ĥ.

Add a flag in nsStyleContext to represent that all descendants are visibility:hidden.ģ. We have already KeyframeEffectReadOnly::CanIgnoreIfNotVisible() to check whether animation influences layout or not.Ī missing part of this bug is a function to check whether all descendant elements are visibility:hidden or not.ġ. > I don't think we could optimize away animations on CSS properties that *do*

> This seems doable, for animations on CSS properties that don't influence (In reply to Daniel Holbert (largely AFK until June 28) from comment #1)

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