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

From: Brad Kemper <brad.kemper@gmail.com>
Date: Mon, 13 Dec 2010 15:20:48 -0800
Message-Id: <B8BDF3CE-38C5-4257-96C3-5A6E00E9077B@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 2:55 PM, Ambrose LI <ambrose.li@gmail.com> wrote:

> 2010/12/13 Brad Kemper <brad.kemper@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.
> The point is that the user who actually connects the projector doesn't
> care about all this. All he/she knows is that when the page is
> displayed a certain way on the screen, it should be displayed exactly
> the same way when projected. The imaginary slide is whatever the
> screen displays, because this is the only link to what the projection
> should look like in the user's point of view.
>> 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.
> Yes, that's correct. The result is the same, but the *rationales* are
> different. For projections, you don't need to argue that the units are
> non-physical, because the units are still physical, but only in an
> imaginary world. This is how we think of our PowerPoint slides, or do
> you not think of them this way?

I never expect an inch in Powerpoint to ever actual measure an exact inch anywhere, except for printing. When I'm editing a slide, I'm usually zoomed in to fill the window pane. So I don't really pay attention to the inches, except maybe to adjust hieight-width proportions. I always assumed the width would be 100%, and the height would be proportional. 

> -- 
> 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 23:21:41 UTC

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