W3C home > Mailing lists > Public > www-style@w3.org > January 2010

Re: Making pt a non-physical unit

From: David Singer <singer@apple.com>
Date: Thu, 7 Jan 2010 15:11:23 -0800
Cc: www-style@w3.org
Message-Id: <639C0373-AE05-473E-9AEA-BE3531103F2C@apple.com>
To: Felix Miata <mrmazda@earthlink.net>

On Jan 7, 2010, at 11:34 , Felix Miata wrote:

> On 2010/01/07 10:43 (GMT-0800) David Singer composed:
>> (personal opinion)
>> 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....We can deem that computer displays are also at
>> normal viewing distance, I suspect.
> Can we? Is, or should be, normal viewing distance coupled to the definition
> of a pt or a px? I should think "normal" might be considerably different for
> users of 8" netbooks, 11.1" laptops, 15.4" laptops, 17" SXGA screens, 23"
> WUXGA screens, 30" Apple Cinema screens, 46" TVs, or groups of two or more
> screens. My normal environment does not permit viewing all four screens at
> once from an equal distance. Which one is "normal"? Are they all "normal"? None?

I don't really mind.  If the computer-maker wants to estimate the viewing distance, or allow the user to set it, that's fine by me.  What the rule ('subtends the same angle at the eye as the given point size text would on a piece of paper held at the standard viewing distance') does is to provide a clear unambiguous meaning to size in most if not all cases -- projection, video-glasses, and so on.  Yes, indeed, 12pt text on a large-screen display that is expected to be viewed from 3 meters away will be physically larger than 12pt text on a computer screen designed to be viewed at normal 'book reading' distances.

So yes, the thought-piece I am floating ties all physical measurements to a definition that is viewing-distance related;  no scaling happens between the physical display and the measurements supplied if and only if the display is deemed to be at the standard viewing distance.  This retains the relationships between physical units (pt, cm, in etc.).

>> If manufacturers want to ship small devices that they deem are necessarily
>> viewed close-up, and thus have a scaling factor also 'built in', that
>> would also be permitted.
> Why not the same for extra large devices? If either or both should, why not
> all?

I'm sorry, I mean to include extra-large as well.  Ballpark displays, where the viewers are often many meters away.  The same sizing rule applies.

> Really, there's no good reason why every user shouldn't be able to scale
> her device's output to her comfort level.

Of course they should.  Ideally they set their actual viewing distance, and their preferred 'normal' font size, and maybe even their preferred zoom factor.

> You mean literal zoom should be a user's only option, with no option for
> intelligence to be applied by the UA?

No;  did I write that?  I'm sorry if I suggested it.  I was trying to say what 'simple zoom's model should be, not that it be the only model or control available.

David Singer
Multimedia and Software Standards, Apple Inc.
Received on Thursday, 7 January 2010 23:11:56 UTC

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