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Re: [CSS21] Single viewport

From: Chris Lilley <chris@w3.org>
Date: Tue, 30 Aug 2005 03:04:09 +0200
Message-ID: <78991246.20050830030409@w3.org>
To: Boris Zbarsky <bzbarsky@mit.edu>
Cc: Ian Hickson <ian@hixie.ch>, www-style@w3.org

On Sunday, August 28, 2005, 11:00:00 PM, Boris wrote:

BZ> Ian Hickson wrote:
>> Multiple viewports on a single canvas in CSS is impossible

BZ> I believe there is just a terminology problem here; as I recall in
BZ> SVG any <svg:svg> element establishes something that SVG calls a
BZ> "viewport". That definition of "viewport" simply differs from the
BZ> CSS one, as far as I can tell.

Right. Thus, stating that CSS establishes a single viewport is fine,
because that is what it does. Sating that all systems cannot have more
than one viewport, when multiple viewports are in fact common, is a
needless conflict.

BZ> That said, there's the question of what "a single canvas" means. For
BZ> example, multiple CSS viewports can be created using <iframe> tags
BZ> in HTML. And to a certain extent these render "on a single canvas",
BZ> since some UAs support translucent iframes.

I agree. I would describe that as multiple viewports operating on a
single canvas.

The same html document being displayed twice in a frameset, on the other
hand, is more like two separate canvases.

BZ> Back to SVG, <foreignObject> should perhaps also create a new CSS viewport
BZ> inside itself...  It's not clear to me, as an implementor, whether it does or not.

It doesn't create an (SVG) viewport but either creates a new (CSS)
viewport or a new (CSS) canvas depending on how you resolve the question
you just posed.

However, changing

> In 9.1.1
> 
>   There is at most one viewport per canvas, but user agents may render
>   to more than one canvas (i.e., provide different views of the same
>   document).
>   http://www.w3.org/TR/2005/WD-CSS21-20050613/visuren.html#viewport

to

> In 9.1.1
> 
> CSS establishes at most one viewport per canvas, but user agents may
> render to more than one canvas (i.e., provide different views of the
> same document).

would help as a first step. Then, as you suggested, please consider
whether an iframe is in fact a new viewport.

-- 
 Chris Lilley                    mailto:chris@w3.org
 Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
Received on Tuesday, 30 August 2005 01:04:17 GMT

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