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Re: Making pt a non-physical unit

From: Jonathan Kew <jonathan@jfkew.plus.com>
Date: Thu, 7 Jan 2010 00:10:25 +0000
Cc: "Robert O'Callahan" <robert@ocallahan.org>
Message-Id: <DBA3E374-8ECE-44F1-8F0B-0BDE186C3E0F@jfkew.plus.com>
To: www-style mailing list <www-style@w3.org>
On 6 Jan 2010, at 23:53, Robert O'Callahan wrote:

> On Thu, Jan 7, 2010 at 12:47 PM, Jonathan Kew <jonathan@jfkew.plus.com> wrote:
>> If we're going to give up the "physical" meaning of pt, and redefine it as 4/3px, then I suggest that we should - for the sake of consistency and designers' sanity - redefine all the "physical" units in the same way, so that 1in remains 72pt, etc. So pc, in, cm, mm, and perhaps a few others (I haven't checked the list) will all change in a coherent way.
>> 
>> For those specialized use cases such as "life size" drawings, touch interface elements, etc., where a certain physical size really is intended - rather than a physical size that made sense on a typical computer monitor or a piece of paper, but should be appropriately scaled when viewing from 6 inches on a phone - I propose that we introduce a new keyword "true". This may be prefixed to any of these existing units, and means that the dimension IS to be interpreted as a true physical size, not scaled according to display size/resolution. (Though it would of course still be subject to overall zooming of the entire laid-out page.)
>> 
>> If allowing an extra optional keyword between the number and units is syntactically difficult, we could instead define new units "truept", "truein", "truecm", etc.
>> 
> I think that would be syntatically necessary, yes.
> 
> This sounds OK to me. I think we wouldn't want "truept" though. Probably "truemm", "truecm" and "truein" would be enough.
> 
> I don't know that this is really necessary, though. I think leaving 'in', 'mm' and 'cm' as physical units would be OK too.

What troubles me about this is the inconsistency it creates between CSS units and the "real world". If these were arbitrary keywords invented purely for CSS, it would be somewhat more acceptable, but pt, pc, in, cm, mm are long-established real-world units with well-known relationships in designers' minds, and it seems fundamentally wrong to redefine them in CSS in such a way as to break that model.

If we were to adopt this approach at all, my thinking is that we should do the full set of "true??" units for the sake of consistency, even if we think some of them (truepc, anyone?) will rarely be used. As for truept: I should be able to specify a touch-screen interface element as being 8 truemm high, and put some text inside it using a font-size of 14 truept.

JK
Received on Thursday, 7 January 2010 00:11:09 GMT

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