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Re: Making pt a non-physical unit

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Thu, 07 Jan 2010 13:55:42 -0500
Message-ID: <4B462E2E.7050604@mit.edu>
To: David Singer <singer@apple.com>
CC: www-style@w3.org
On 1/7/10 1:43 PM, David Singer wrote:
> It's fairly clear that physical measurements apply to material that is at 'normal reading distance' (and I bet there is an ISO standard for that), or is back-calculated from its actual distance to what size it would be at normal reading distance.  That's why powerpoint works on projectors;  if you are at the distance from the screen such that the screen and a piece of paper held at reading distance subtend about the same view angle, it all works.  Perhaps this should apply to all physical units:  1in means that distance that subtends the same angle at the eye as 1in would at the standard viewing distance, and so on.

This is effectively Jonathan Kew's proposal.

> What you write below does not sound right at all, to me.  A zoomed version of a page should be just that, zoomed;  not re-styled as if the designer had asked for fonts at twice the design size.
>>
>> On Jan 7, 2010, at 9:23 , Boris Zbarsky wrote:
>>> I would hope not.  A UA should be choosing the design size most closely corresponding to actual rendered size, as much as possible.  For example, if you have a page that says it wants 12px fonts and it's zoomed to 2x in Gecko, Gecko will use the 24px font instead of scaling the 12px font.

What I wrote was simply a characterization of how Gecko's "page zoom" 
feature works.  It does not claim to be a pixel-for-pixel zoom, nor is it.

Then again, neither is Safari's (at least not desktop Safari).  Nor 
Opera's.  Nor Chrome's.  I don't have IE on hand to test.

Try it:  open http://en.wikipedia.org/wiki/Main_Page in any of those 
browsers, then zoom in in any of the above browsers.  Observe that the 
places where line-breaks happen change.  So the engine is clearly not 
doing a pixel-for-pixel zoom but rather a relayout at the same device 
width and height using a different mapping from CSS lengths to device 
pixels.

Maybe I misunderstood your objection, though?

-Boris
Received on Thursday, 7 January 2010 19:12:10 GMT

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