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Re: [css-transforms] How should overflow be calculated for perspective transforms?

From: Simon Fraser <smfr@me.com>
Date: Mon, 07 Dec 2015 12:12:17 -0800
Cc: "www-style@w3.org" <www-style@w3.org>
Message-id: <2DEAB33D-69E9-475A-B29D-805BA3C9ACEF@me.com>
To: Matt Woodrow <mwoodrow@mozilla.com>
> On Nov 9, 2015, at 6:23 PM, Matt Woodrow <mwoodrow@mozilla.com> wrote:
> 
> Take the following example: https://bug1198135.bmoattachments.org/attachment.cgi?id=8684006
> 
> In Firefox, you can scroll well beyond the end of the content. This is because we're computing the overflow area of the elements (with perspective transforms included) as they exist at scrollTop == 0. This doesn't take into account that the perspective transform is dependent on scroll position, and the 'real' overflow area actually shrinks as you scroll.
> 
> In both Safari and Chrome you can't scroll the entire orange element into view. This appears to be because overflow is being computed without the perspective transforms applied, and perspective is just a rendering effect. Commenting out the perspective rule from the css helps show this.
> 
> The Transforms spec says:
> 
> > Therefore, if the value of the overflow property is scroll or auto, scrollbars will appear as needed to see content that is transformed outside the visible area.
> 
> Should the spec be updated to reflect what Safari/Chrome are implementing? Or should it remain as is (probably with some clarification), and the browser behaviour be fixed?

I would consider the WebKit behavior as a bug (though not one that is a high priority to fix).

Simon
Received on Monday, 7 December 2015 20:13:12 UTC

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