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Re: CSS3 font-weight, OFF OS2.usWeightClass, and weights which are not a multiple of 100.

From: Thomas Phinney <thomas.phinney@gmail.com>
Date: Wed, 9 Feb 2011 07:11:09 -0800
Message-Id: <3054C597-796B-43C0-B23C-D349239CBCC0@gmail.com>
Cc: "www-font@w3.org" <www-font@w3.org>, "www-svg@w3.org" <www-svg@w3.org>
To: Chris Lilley <chris@w3.org>
I'll just note that if one wants a system to deal with real-world fonts, it should deal with inputs for usWeightClass that are any integer from 0-1000.

I am curious as to what everyone thinks a font creator should do if they have a family with three or more weights that are heavier than "bold" (which maps to 700).

In our collection of about two thousand web fonts, as I recall there are four such cases.

This is aside from the many other cases where values aren't in hundreds, etc.

I remain puzzled that CSS 3 will remain deliberately incompatible with real fonts in this area.

T

On Feb 9, 2011, at 6:20, Chris Lilley <chris@w3.org> wrote:

> Hello www-font,
> 
> Open Font Format (OFF [1]) states that OS2.usWeightClass is a 2-byte unsigned short and describes it as
> 
> "Indicates the visual weight (degree of blackness or thickness of strokes) of the characters in the
> font."
> 
> There is an accompanying table which relates particular values 9100, 200 etc) to textual descriptions (e.g. 'Thin') and C definitions from windows.h (e.g. FW_THIN).
> 
> Values which are not multiples of 100 are not specifically allowed and not specifically disallowed; they just don't have a defined mapping to those two string sources.
> 
> I have seen fonts with weights like 250 etc so I conclude that in OFF, OS2.usWeightClass is a continuous range of cardinal numbers.
> 
> CSS3 Fonts states that the font-weight property [2], used to request styling, is an ordered sequence of tokens:
> 
> "100 to 900
>    These values form an ordered sequence, where each number indicates a weight that is at least as dark as its predecessor."
> 
> and 
> 
> "Font formats that use a scale other than a nine step scale should map their scale onto the CSS scale"
> 
> and that the font-weight descriptor [3], used to tell CSS about the weight of a particular font, is also a discrete series of tokens:
> 
> "Value:    normal | bold | 100 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900"
> 
> so I conclude that values like 250 are explicitly disallowed.
> 
> The point of this email is to ask:
> 
> a) are the above assumptions correct?
> b) if a value which is not a multiple of 100 is used in the CSS style system, (e.g by script, or by direct specification in a style sheet, or by animation) then it gets mapped to the nearest multiple of 100?
> c) thus, animation of the font-weight property should be discrete, not continuous, despite the fact that fonts with wights that are not a multiple of 100 may be available, as the CSS style shystem does not expose their native weights?
> 
> Tracker, this relates to SVG-ACTION-2936
> 
> 
> [1] ISO 14496-11:2009(E)
> PDF downloadable at no charge by agreeing to
> http://standards.iso.org/ittf/licence.html
> 
> [2] http://dev.w3.org/csswg/css3-fonts/#font-weight-prop
> 
> [3] http://dev.w3.org/csswg/css3-fonts/#font-prop-desc
> 
> 
> -- 
> Chris Lilley   Technical Director, Interaction Domain                 
> W3C Graphics Activity Lead, Fonts Activity Lead
> Co-Chair, W3C Hypertext CG
> Member, CSS, WebFonts, SVG Working Groups
> 
> 
Received on Wednesday, 9 February 2011 15:11:52 GMT

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