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Re: [CSS21] 4.3.2 Lengths (reference pixel?)

From: Brad Kemper <brad.kemper@gmail.com>
Date: Mon, 13 Dec 2010 14:36:29 -0800
Message-Id: <B651B260-C59B-4D89-8864-2877E8792296@gmail.com>
Cc: "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de>, "www-style@w3.org" <www-style@w3.org>
To: Ambrose LI <ambrose.li@gmail.com>
On Dec 13, 2010, at 11:51 AM, Ambrose LI <ambrose.li@gmail.com> wrote:

>> The point you seem to be missing is that we are not trying to define inches and centimeters. We are defining the CSS units of 'in' and 'cm'. In some contexts, these have a direct relationship to inches and centimeters, and in others they do not. On projector screens, for instance, 'in' is just about as divorced in meaning from a physical "inch" as it is from the preposition "in".
>> 
> 
> As I have pointed out before, the usual understanding of mm and in for
> projector screens remains physical. An imaginary slide, with imaginary
> real dimensions and where mm and in have their usual real meanings, is
> projected onto a physical surface at an unknown distance.

If I understand you correctly, this would require us to agree on a standard "slide" height instead, and use that when the image is to be projected. That does not seem like a very useful way to author anything, not nearly as useful as always having a consistent size relationship. As well, it would only work if the UA knew that it was hooked up to a projector, which I think would be almost never. The UA is lucky if it even knows the size of the device pixels in a CRT. 

But what you are describing, a virtual surface that that can be scaled by the projector, is not that different from what we already decided on, which is pretty much a virtual surface that can be scaled by the px size. It's just that the latter is more workable for authors who want to maintain consistent size relationships of their design elements. Whereas the former means that an inch is still rarely an inch in the final viewable surface anyway, due to widespread unreliability of determining the final resolution of the display or projection. 


> The units
> still mean the same thing, and if they do not mean the same thing then
> it'd be impossible to predict what the projection will look like.
> 
> -- 
> cheers,
> -ambrose
> 
> does anyone know how to fix Snow Leopard? it broke input method
> switching and is causing many typing mistakes and is very annoying
Received on Monday, 13 December 2010 22:37:15 GMT

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