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Re: Specifying window.performance.now()

From: Sigbjørn Vik <sigbjorn@opera.com>
Date: Wed, 29 Feb 2012 11:39:29 +0100
To: public-web-perf@w3.org
Message-ID: <op.wafrv3pdpi0hod@india.oslo.osa>
On Tue, 28 Feb 2012 20:47:00 +0100, Jatinder Mann <jmann@microsoft.com>  
wrote:

> I have uploaded a draft of the High Resolution Time spec here:  
> http://dvcs.w3.org/hg/webperf/raw-file/tip/specs/HighResolutionTime/Overview.html.  
> Please review the spec and provide feedback.

"Without sub-millisecond resolution, a developer can only determine if an  
animation is drawing at 58.8 FPS or 62.5 FPS."
A technically correct way of saying this would be e.g. "a developer can  
only determine such a framerate to within 3.5 FPS". Technically, with a  
reading of 17, the FPS is determined to be in the range 57-61.

"the number of milliseconds from the start of the navigation of the root  
document"
Is the "start of the navigation" well enough defined? Should we link it to  
one of the other performance specs to tie it down absolutely?
This also allows a cross-origin iframe to tell how long the parent has  
been alive, which I believe is not possible now. This is a slight privacy  
leak, which can easily be avoided. For instance remove "root" from the  
statement, or change it to "the topmost same-origin document", with a  
suitable definition of same-origin. I believe the second is better, it is  
useful for same-origin documents to have the same timestamps. For  
cross-origin documents this should normally not be required. This should  
also be recorded in the privacy section.

-- 
Sigbjørn Vik
Core Quality Services
Opera Software
Received on Wednesday, 29 February 2012 10:40:17 GMT

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